app: make the relay come back by itself, and report within seconds

Two faults found by watching it run. The heartbeat was the only cadence,
so the first pass ran before mDNS discovery finished, saw nothing, and
then sat silent for two minutes - precisely when someone has just
switched the relay on and is watching for it to work. It now polls every
five seconds until the first successful report, then settles.

And nothing restarted the service after a reboot or an app update, which
is the most common way it dies during development. A relay that has
quietly stopped is worse than one never switched on: the endpoint it last
published keeps looking authoritative while pointing at a port nothing is
listening on. RelayBootReceiver handles BOOT_COMPLETED and
MY_PACKAGE_REPLACED, debug builds only, and does nothing unless the relay
was already on.

Verified end to end: installing this build triggered the receiver and the
phone reported its endpoint 7 seconds later, unattended.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitea/workflows/build-server.yml

@@ -15,7 +15,13 @@
 #                        container registry (docker login → unauthorized).
 #                        Create: user Settings → Applications → Generate token.
 #   REGISTRY_USER        optional; defaults to the pushing actor's username.
-# The release job needs only the built-in GITHUB_TOKEN.
+#   RELEASE_SIGNING_KEY  base64 ed25519 seed that signs SHA256SUMS. Self-updating
+#                        servers verify the signature against the public key baked
+#                        into the binary (selfupdate.DefaultPublicKeyB64) and REFUSE
+#                        unsigned releases, so this job hard-fails without it —
+#                        a release nobody can install is better failed loudly here.
+#                        Mint a pair with: go run ./cmd/release-sign -gen
+# The release job otherwise needs only the built-in GITHUB_TOKEN.
 
 name: server-release
 on:
@@ -44,6 +50,18 @@ jobs:
           done
           (cd ../dist && sha256sum * > SHA256SUMS)
 
+      - name: Sign SHA256SUMS
+        working-directory: server
+        env:
+          RELEASE_SIGNING_KEY: ${{ secrets.RELEASE_SIGNING_KEY }}
+        run: |
+          [ -n "$RELEASE_SIGNING_KEY" ] || { echo "::error::secret RELEASE_SIGNING_KEY is missing — self-updating servers refuse unsigned releases, so publishing one would strand the fleet. Add it under Settings → Actions → Secrets."; exit 1; }
+          go run ./cmd/release-sign ../dist/SHA256SUMS
+          # Verify with the key baked into the binary we just built — catches a
+          # secret that does not match DefaultPublicKeyB64 before it ships.
+          PUB=$(grep -o 'DefaultPublicKeyB64 = "[^"]*"' internal/selfupdate/selfupdate.go | cut -d'"' -f2)
+          go run ./cmd/release-sign -verify -pub "$PUB" ../dist/SHA256SUMS
+
       - name: Create release + attach binaries
         env:
           TOKEN: ${{ secrets.GITHUB_TOKEN }}

CLAUDE.md

@@ -145,6 +145,17 @@ First build downloads AGP/Compose/Shizuku from Google Maven + Maven Central.
   Shizuku, **toggle Wireless debugging off/on** — Shizuku keeps running (separate process), a fresh
   port + mDNS record appear, and the beacon/connector recover. Plan the Shizuku-tier dev loop
   around this (or USB, if ever available).
+- **A poisoned Gradle *build cache* entry can silently drop a whole module from the APK.**
+  Symptom: the app dies with `ClassNotFoundException` for a class that plainly exists, while the
+  build is green and `./gradlew :app:dependencies` lists the module on `debugRuntimeClasspath`.
+  The module's own jar is correct; its code simply never reaches AGP's intermediates. `clean`,
+  `rm -rf */build` and `--rerun-tasks` all fail to fix it, because **none of them touch the build
+  cache** — look for `compileKotlin FROM-CACHE` in the log. Fix: rebuild with `--no-build-cache`.
+  Verify by grepping the APK's dex for a string literal that only that module defines; grepping for
+  a *class name* proves nothing, because callers carry the name as a reference whether or not the
+  class is packaged:
+  `unzip -o -q app-debug.apk "classes*.dex" && grep -a "pin-sha256:" *.dex`
+  Suspect this whenever a runtime failure contradicts a successful build.
 - **Empty-jar race with the IDE.** VSCodium's Java/Kotlin extension runs its own Gradle daemon on
   the same project; when it overlaps a CLI build, a module's `build/libs/*.jar` can end up
   containing only a manifest, and Gradle then considers `jar` up-to-date. Dependent modules fail

docs/build-status.md

@@ -211,8 +211,8 @@ Two collection-loop gotchas found while driving the phone over USB:
 2. ~~If `trace.errqueue_reachable` = PARTIAL, add a C-over-JNI errqueue shim.~~ **Retired** —
    SUPPORTED on both known devices; `traceroute.udp4` reads real hops via `Os.recvmsg` +
    `StructMsghdr` reflection, so no `:native` module is needed.
-3. Start the Go server skeleton (enrollment + profile + sessions + UDP echo with observation
-   blocks + canary-DNS reference records) per probe-protocol.md.
+3. ~~Start the Go server skeleton per probe-protocol.md.~~ **Shipped** — live on fmr since
+   v0.2.0 (2026-07-31); see the server sections below.
 4. Fold confirmed capabilities into the production `core-probe` / `core-shizuku` modules.
 
 ## Production probe server — LIVE on dedicated VM "fmr" (2026-07-31)
@@ -222,7 +222,7 @@ SSH only — verified untouched by the daemon (explicit multi-address binds, no
 Control: fmr-1:8443 (SPKI pin `zRV9qkiLnRexAeh4RrSfJzbPWO+U/2Oj2/NVM/KfXlg=`, verified
 externally over v4+v6). UDP data plane on all four service addresses :8442 — the second IP is
 the stun-5780 substrate. Daily randomized self-update timer installed (checksum-verified
-against SHA256SUMS; signature verification still TODO before treating the source as untrusted).
+against SHA256SUMS; signature verification landed 2026-08-02 — see "Release signing" below).
 Host config in `/etc/echolot-server.env`. SSH access for sessions: `ssh claude-echolot`.
 
 ## Server v0.3.0 — STUN + TCP echo + observations + actions (2026-07-31)
@@ -1054,3 +1054,436 @@ Four consequences that decide whether it is worth it:
 What keeps this possible: uploads are already stored byte-for-byte as received, and every index
 field is derived in one function (`runs.Put`). The thing to avoid is admin features that *require*
 reading content — those would have to be unbuilt later.
+
+### App sign-in, and an undisclosed dependency it surfaced (2026-08-01)
+The app can now sign in to the server's identity provider: authorization code with PKCE, a
+`Sign in` card in settings, and the `echolot://auth` redirect handled alongside the enrolment one
+(told apart by host, since one spends a token and the other completes an authorization).
+
+The detail that decides whether this works on a real phone: **the PKCE verifier is written to
+storage before the browser opens**, not held in memory. Handing control to a browser backgrounds
+the process and Android may kill it; the callback then arrives at a fresh process. An in-memory
+verifier works on a developer's device and fails under memory pressure, which is the worst way for
+a sign-in to break.
+
+Nothing from the IdP is retained. The ID token proves who is signing in, once, and the device
+credential authenticates everything after — no access tokens stored, no refresh tokens rotated.
+
+**A server remains entirely optional.** All eight probes are device-tier; `serverConfigured` gates
+only upload and the account. But answering that question exposed something worth fixing: two probes
+hardcode the reference deployment —
+
+```kotlin
+DnsCanaryProbe(canaryZone = "c.echo-lot.app", ...)   // "Hardcoded to the reference deployment"
+StunProbe(serverHost = "fmr-1.echo-lot.app")
+```
+
+so a user with no server of their own still sends DNS and STUN traffic to fmr without being told.
+For a tool that goes to this much trouble over what leaves the device, an undisclosed dependency on
+a third party's infrastructure is the wrong default. It should prefer the configured server, and be
+explicit when there is none. **Closed** — both probes take the enrolled server from settings
+(canary zone learned from the profile, cleared on re-enroll) and report themselves SKIPPED with
+the reason when none is configured.
+
+### v6.broken was a false positive waiting to happen (2026-08-01)
+A phone could not open `https://fmr.echo-lot.app` while loading the same server by IP literal
+perfectly well. Two things came out of chasing it.
+
+**The admin UI is IPv6-only, by consequence rather than intent.** `fmr.echo-lot.app` has an AAAA
+and no A record — verified identical at Cloudflare, Google and Quad9, so DNS itself is healthy.
+That follows from reserving all four measurement addresses for testing, which left only `::2` for
+management, and `::2` has no IPv4 counterpart. Any client without working IPv6 sees an unreachable
+admin interface — a poor property for the interface you reach *from the networks you are debugging*.
+
+**And the app's own `v6.broken` finding was unsound.** It fired on exactly one signal — ICMPv6 echo
+getting no reply — with `Confidence.HIGH`. ICMPv6 echo is widely filtered on networks where IPv6
+works fine, which is precisely what that phone demonstrated: no ICMPv6 replies, working IPv6 TCP.
+The finding asserted a cause it had no evidence for, which is the same class of error as the
+multi-homed `100 % downstream loss` earlier: a confident measurement of something that was not
+happening.
+
+Now `v6.no_icmp_reply`, severity low, confidence medium, and the text names *both* explanations
+instead of choosing one. It is still worth reporting, because filtered ICMPv6 breaks Path MTU
+Discovery — large packets vanish rather than being reported as too big — which is a real fault even
+when IPv6 works.
+
+The proper fix is corroboration: attempt a real IPv6 connection and only call it broken when that
+fails too. That needs a target, which runs into the hardcoded-reference-deployment issue already
+open above. **Both closed 2026-08-02** — see "Corroborated IPv6 findings" below.
+
+## Per-network probing is blocked while a VPN is up (2026-08-01)
+
+`Network.bindSocket()` fails with `EPERM` for every underlying network when a VPN holds the
+default route — verified on the OnePlus 15 with Netbird active: `Binding socket to network 101
+failed: EPERM` for both cellular and wifi. This is Android preventing VPN leaks, not a bug to work
+around, and it means the whole per-network measurement approach is unavailable to any user with a
+VPN connected. Worth deciding deliberately rather than discovering per report:
+
+- The run currently succeeds and simply measures nothing per network. Honest, but silent — the
+  document records `attempted: false` and the UI says green.
+- A user with a corporate VPN permanently on would get a green run that measured almost nothing.
+
+Options are to detect the VPN and say so plainly ("this network cannot be measured while a VPN is
+active"), to measure the tunnel itself as the network under test, or both. **Decided and built
+2026-08-02**: say so plainly, everywhere the run is read — see "Constrained runs" below.
+
+Related: `icmp.ping6` now records `attempted` alongside `ok` per network, because collapsing them
+made the app report "IPv6 is configured, but ICMPv6 gets no reply" about an interface it had never
+succeeded in sending on — a claim about the user's carrier with no evidence behind it.
+
+## Reserved measurement addresses, and the web UI on both families (2026-08-01)
+
+fmr has two IPv4 (.150/.151) and three IPv6 (::150/::151/::2) addresses. `.150`/`::150` now carry
+the services; `.151`/`::151` are reserved for measurement, declared in `ECHOLOT_RESERVED_ADDRS`.
+
+Reserved does **not** mean silent. The UDP data plane, the canary DNS and STUN's RFC 5780 alternate
+all belong there — reserving an address and then forbidding the measurements that need it would
+defeat the purpose. What must never appear is a service, and above all not ports 80 or 443: a
+handshake completing on a port known not to be listening is what proves interception, and that
+proof survives exactly as long as nothing binds those ports. `config.CheckReserved` enforces it at
+startup, refusing wildcard binds outright (every listener defaults to `:port`, so the next one added
+will claim reserved addresses without anyone deciding to).
+
+The first version of the guard was too strict and the live config caught it: it would have refused
+the existing UDP and DNS binds on `.151`. The rule is about services and web ports, not about
+listening at all.
+
+**The adb-beacon receiver was wildcard-bound to `0.0.0.0:443`**, occupying port 443 on every IPv4
+address including the reserved one — so the IPv4 interception test had been compromised for as long
+as it had been running, silently. It is now `systemctl disable --now echolot-adb-beacon`; restore
+with `systemctl enable --now`. Note what this implies: the guard covers this server's own listeners,
+and a stray process outside its config can still pollute a reserved address. A startup probe that
+*verifies* 80/443 are actually free on the reserved addresses would be a stronger guarantee than
+checking our own configuration — built 2026-08-02 (`selftest.ReservedWebPortsFree`, fatal at
+startup when anything is listening there).
+
+The admin UI and the ACME responder now take comma-separated addresses like every other listener;
+they were single-address, which is why the UI could only ever live on `::2`. It serves on `.150:443` and
+`[::150]:443`; sshd on `.150:2322` and `[::150]:2322`.
+
+`::2` is gone entirely — unbound, then removed from `/etc/systemd/network/ext.network`. The
+transition kept it bound throughout and dropped it only after the CNAME landed, because removing it
+first would have broken both the UI and ACME renewal for the very name the certificate is issued
+to. Listeners came off before the address did, in that order, or the services would have failed to
+bind on restart.
+
+Verified after a full reboot: `fmr.echo-lot.app` answers 200 over both families, `.151`/`::151` are
+closed on 80 and 443, canary DNS is still up on `.151`, and neither `::2` nor the beacon returns.
+(`echolot-server` is `After=network-online.target` with `Restart=on-failure`, which is what makes
+binding specific addresses safe across a boot — a wildcard bind would not have needed it, and that
+is the trade for the reserved addresses being meaningful.)
+
+The point of all this: `fmr.echo-lot.app` gained an A record, so the server stopped being reachable
+only over IPv6 — which is what made it unreachable from a phone with no working IPv6, presenting as
+"this host does not exist" in two different browsers.
+
+### If the beacon comes back, it belongs in the web UI
+
+Not as a separate listener. The receiver being its own Python service on `0.0.0.0:443` is exactly
+what silently compromised the reserved address, and a second process racing for a port is a
+recurring problem rather than a one-off: whoever loses the race simply fails to start, and on a
+reboot which one that is comes down to unit ordering.
+
+Folding it in costs little and settles several things at once. It would be two routes on the admin
+UI (`POST` the observed adb port, `GET /apk` for the staged build), behind the TLS the UI already
+terminates and the certificate it already renews, with no extra port and no wildcard. It also gets
+authentication for free — the current receiver accepts a port report from anyone who can reach it,
+which is tolerable for a dev tool on a trusted network and not something to keep once it lives
+beside an admin session.
+
+The one thing that changes on the device side is that the POST becomes HTTPS. That is a real
+certificate rather than a self-signed one, so it costs a URL scheme rather than any trust plumbing.
+
+## The control plane shares port 443 (2026-08-01)
+
+`fmr-1.echo-lot.app:443` is the control plane, `fmr.echo-lot.app:443` the admin UI, both on
+`.150`/`::150`, one listener, selected by SNI for the certificate and by `Host` for the handler.
+
+The reason is not tidiness, it is reachability. Captive portals, hotel wifi and corporate firewalls
+routinely permit only 80 and 443 — which is exactly the population of networks this tool exists to
+diagnose. A control plane on 8443 is unreachable precisely when it matters most, and it fails as
+"cannot reach server", which tells the user nothing.
+
+They cannot share a certificate, which is why this needs two names. The control plane is trusted by
+SPKI pin and so uses a long-lived self-signed certificate; a browser needs one a CA vouches for.
+One name on one port is one certificate, so the port can only be shared by splitting the names.
+Pinning the Let's Encrypt key instead was considered and rejected: it survives renewal only while
+key reuse holds, so a routine key rotation would brick the whole fleet.
+
+Verified per SNI on 443: `fmr.echo-lot.app` serves `issuer=Let's Encrypt`, `fmr-1.echo-lot.app`
+serves the self-signed cert whose pin is unchanged (`zRV9…Xlg=`), `/v1/profile` answers 401 on the
+control name and 303 to the login page on the UI name.
+
+**8443 stays open.** Devices enrolled before this carry that URL in their settings, and closing it
+for the sake of a port number would strand every one of them. It can go once no enrolled device
+still points at it — not before.
+
+The rule from the naming change still binds: `fmr` may be a CNAME to exactly one host and never a
+multi-address record, because a pinned client that reaches a different key does not fail over.
+
+## Constrained runs: a VPN'd run now says so, everywhere (2026-08-02, app 0.2.1)
+
+The measurement schema gained a top-level `constraints` block (§3) and the app now fills it.
+`ConstraintDetector` (core-probe) runs before any probe: one throwaway `Network.bindSocket()` per
+non-VPN network, plus a transport check for an active VPN. The result lands in three places, and
+all three are deliberate:
+
+- **`run.constraints`** — for machines. A server aggregating thousands of runs can now separate
+  "measured a healthy network" from "measured almost nothing through a tunnel"; the shapes were
+  identical before.
+- **A `measurement.vpn_constrained` finding** — for the person reading this run, naming the
+  interfaces that went unmeasured. A constrained run with a quiet findings list still reads as
+  "nothing wrong here".
+- **The §7.3 verdict** — `Verdicts.derive` takes the constraints and returns INCONCLUSIVE
+  outright for a per-network-blocked run, whatever the category lights say; the run screen shows
+  an amber "Measured through a VPN" banner above the verdict so INCONCLUSIVE reads as the OS
+  refusing, not the app failing.
+
+Detection is one bind per network rather than parsing per-test `attempted:false` breadcrumbs, so
+it cannot drift when probe evidence formats change.
+
+## Corroborated IPv6 findings: v6.broken is back, with evidence (2026-08-02, app 0.2.1)
+
+The new `V6ConnectProbe` (test type `v6.brokenness`) attempts a real TCP connection over IPv6 to
+the configured server's :443, per network that *claims* IPv6 (global address or v6 default
+route) — IPv4-only networks are not attempted, since their failure is by design and would
+manufacture the exact false positive this exists to kill. The finding derivation is now three-way:
+
+- ICMPv6 silent, TCP works → `v6.no_icmp_reply` at **high** confidence, retitled "ICMPv6 is
+  filtered here — IPv6 itself works" (still reported: filtered ICMPv6 breaks PMTUD).
+- ICMPv6 silent, TCP fails too → **`v6.broken`** (high severity, reinstated in the registry +
+  findings-registry.md): two independent transports silent on a network advertising IPv6.
+- No corroboration (no server configured, or the connect never got as far as sending) → the
+  two-explanation `v6.no_icmp_reply` at medium confidence, unchanged.
+
+Like STUN and the canary, the probe SKIPs honestly when no server is configured — corroboration
+is a benefit of enrollment, not a reason to borrow fmr.
+
+## Server: reserved 80/443 verified against the OS, and signed releases (2026-08-02)
+
+**Reserved-address startup probe.** `serve()` now proves 80/443 are actually free on every
+`ECHOLOT_RESERVED_ADDRS` address before starting: a throwaway bind per port
+(`selftest.ReservedWebPortsFree`), fatal on EADDRINUSE with the offending address named — the
+check `CheckReserved` cannot do, because a stray process outside our config (the adb-beacon
+receiver on `0.0.0.0:443` was exactly that) is invisible to configuration checks. Bind errors
+that are not "in use" (typo'd address, address not on this host) warn instead of refusing —
+they are config problems, not pollution.
+
+**Release signing.** Self-update now trusts a signature, not a host. CI signs `SHA256SUMS` with
+an ed25519 key (`relsign` package, `cmd/release-sign`) and the updater refuses any release whose
+`SHA256SUMS.sig` is missing or does not verify against the public key baked into the binary
+(`selfupdate.DefaultPublicKeyB64`; operators with their own pipeline override via
+`ECHOLOT_SELF_UPDATE_PUBKEY`). The private key exists in exactly two places: the Gitea Actions
+secret `RELEASE_SIGNING_KEY`, and the offline original on the dev PC at
+`~/.echolot/release-signing-key`. It is deliberately NOT on fmr and NOT in the repo — a
+compromised release host can withhold updates but no longer inject one. CI hard-fails when the
+secret is missing (an unsigned release would strand every verifying server) and cross-checks the
+signature against the key in the source it just built.
+
+**ACTION REQUIRED before the next `server-v*` tag:** add the Gitea repo secret
+`RELEASE_SIGNING_KEY` (Settings → Actions → Secrets) with the contents of
+`~/.echolot/release-signing-key` from the dev PC. Ordering is safe: the currently deployed
+v0.3.x updater does not verify, so it will happily install the first signed release; every
+release after that is verified. **Done 2026-08-02** — the secret is in place. (The "v0.3.x"
+above should read "the currently deployed release": deployments had moved on to v0.9.x by the
+time signing landed; the point — the deployed updater predates verification and will accept the
+first signed release — is unchanged.)
+
+## Prober fold: traceroute.udp4 and the mDNS inventory go production (2026-08-02, app 0.2.2)
+
+The two highest-value validated capabilities moved from the prober into `core-probe`:
+
+- **`traceroute.udp4`** (`TracerouteProbe`): UDP traceroute reading ICMP time-exceeded off the
+  socket error queue via `Os.recvmsg(MSG_ERRQUEUE)` through the reflection facade — no root, no
+  raw socket, no JNI, ~250 ms for six hops. Emits the schema's `TracerouteEvidence` (rtt in ns).
+  `OsAbi` came with it, including the measured fact that `Os.getsockoptInt` exists on neither
+  known device, so PMTU must always be read from the errqueue (`ee_info`), never
+  `getsockopt(IP_MTU)`. The load-bearing line survived the port: EAGAIN out of the reflected
+  `recvmsg` means "queue empty", not failure.
+- **`local.mdns_inventory`** (`MdnsInventoryProbe`): MulticastLock + NSD discovery, the service
+  inventory that doubles as the VLAN-leakage detector. Both hardware lessons kept: the
+  `_services._dns-sd._udp.` meta-query returns 0 beside live services on both devices (so the
+  concrete types are the measurement and the meta-query result is itself evidence), and the
+  listen window is 10 s because 4 s missed services.
+
+Still to fold, in order: the Shizuku dump *parsers* (the raw `link.ip_monitor` captures already
+hold two divergent vendor formats that could feed `link.ra_source` and `sec.arp_watch`);
+`multinetwork.request_and_bind` (extend ConstraintDetector to *request* transports rather than
+only probing present ones); `peer.ble_advertise` (needs three new permissions and a peer mode to
+exist first).
+
+## Server v0.9.2: trains, real TTL/DSCP/ECN, rate limits (2026-08-02)
+
+The spec-vs-implementation gap audit closed its top items; protocol_version 1.0.0 → 1.0.1
+(additive — below 1.0.0 the minor is the breaking axis, and nothing here breaks an old client):
+
+- **Upstream trains** (§3.2, types 0x03/0x04/0x05): per-train bounded columnar buffer (8192
+  rows, head kept on overflow with `Truncated` set — mirrors the schema's `evidence_truncated`
+  honesty), TRAIN_REPORT split across ≤1200-byte datagrams, grant-free with the §3.4 argument
+  spelled out (a 17-byte report row answers a ≥36-byte HMAC-valid packet). Unknown train id
+  gets a zero-row report: "nothing arrived" is an answer. Also surfaced as `udp.trains` in the
+  observations API.
+- **Real TTL/DSCP/ECN observation** (§3.3): the read loop is `ReadMsgUDPAddrPort` with
+  IP_RECVTTL/IP_RECVTOS/IPV6_RECVHOPLIMIT/IPV6_RECVTCLASS cmsgs on Linux; `0xFF` stays the
+  "not observed" sentinel elsewhere. This unblocks `sec.dscp_ecn_survival` both directions,
+  paired with the new `dscp` parameter on `downtrain` (validated 0–63, refused not clamped,
+  `dscp_applied` in the response).
+- **Rate limiting** (§2.5, was entirely absent): token buckets keyed per credential AND per
+  source IP; 429 + Retry-After on session/action creation (`/v1/profile` stays ungated), silent
+  drop on the data plane — charged after the HMAC gate so a spoofed flood cannot drain a
+  victim's budget, before the replay window so a dropped seq stays usable. UDP ceilings default
+  above the largest legitimate run (a 200 Mbps throughput test), because a rate limit that
+  clips a real measurement produces a confidently wrong number.
+- **`action_id` in every granted packet** (§5/§9): payload bytes [8:16] across all granted
+  types, so overlapping actions are attributable. Verified the deployed Kotlin client parses
+  only ECHO_RESP and MTU_ACK payloads, so the reshuffle strands nobody.
+- **Canary log retention**: the stated 24 h privacy default is now enforced
+  (`ECHOLOT_DNS_LOG_RETENTION_H`), where before the log was time-unbounded.
+- **`POST /admin/enroll-tokens`** now answers the spec's JSON shape under content negotiation;
+  the README's curl works as documented.
+- Spec §2.3 registry gained `downtrain` and `tcp-echo`, which the server had been advertising
+  as strings a conformant client must ignore.
+
+Client-side counterparts still to build: sending 0x03 trains + parsing 0x05 reports
+(`train.udp_updown`), and passing `dscp` on downtrain actions.
+
+## ⚠ Version lineage broken: fmr runs v0.11.2, the repo's tags stop at v0.9.x (2026-08-02)
+
+Discovered while preparing to self-update fmr to the freshly released server-v0.9.2:
+**fmr runs v0.11.2** (binary installed 2026-08-02 08:51), but this repo's remote has tags only
+up to `server-v0.9.1`, master fast-forwarded cleanly from this machine, there is no v0.10/v0.11
+release in Gitea, no source checkout or Go toolchain on fmr, and no deploy script in this repo
+that stamps versions. Conclusion: v0.11.2 was cross-built from a clone whose commits were never
+pushed — presumably another dev machine.
+
+Consequences until resolved:
+- **Do NOT run `--self-update` on fmr.** Gitea's `/releases/latest` is the *newest-created*
+  release, which is now `server-v0.9.2` — semantically older than the deployed binary; the
+  updater compares strings, not SemVer, and would happily "update" v0.11.2 down to it. No
+  automatic risk exists (fmr has no update timer installed, only the cert timer), but a manual
+  run would downgrade.
+- The next real release must be tagged **above v0.11.2** (e.g. `server-v0.11.3` or `v0.12.0`)
+  *after* the missing commits are pushed, so "latest" becomes truly latest again.
+- The unpushed v0.10–v0.11 work needs to be found and pushed from whichever machine built it,
+  or the deployed binary's provenance re-established some other way, before the release channel
+  can be trusted again.
+
+**Resolved same day.** The binary itself settled it: `go version -m` on the deployed executable
+shows `vcs.revision=d5b1bab` — a commit on this repo's master — built 2026-08-02 08:36 UTC with a
+hand-stamped `-X main.Version=v0.11.2` and a dirty tree (`vcs.modified=true`, the then-uncommitted
+schema doc). An earlier session stamped release numbers ahead of the tag line; no code was ever
+missing. Current master is tagged and released as **server-v0.11.3** (signed), restoring a
+monotonic, tag-backed lineage above the deployed number. The rule going forward: **the version a
+binary is stamped with must be a pushed `server-v*` tag** — an ad-hoc stamp above the tag line
+poisons `/releases/latest` for the string-comparing updater the moment anyone tags honestly again.
+The stale `server-v0.9.2` release (same code lineage, wrong number, created during the confusion)
+remains in Gitea but is harmless now that v0.11.3 outranks it as latest.
+
+## LLDP and CDP are root-tier, and that is a hard boundary (2026-08-02)
+
+Asked for alongside SSDP in long mode; they belong to a different tier and no amount of app-side
+cleverness moves them. LLDP is an EtherType `0x88CC` frame to `01:80:C2:00:00:0E`; CDP is an
+LLC/SNAP frame to `01:00:0C:CC:CC:CC`. Neither is IP, so neither is ever delivered to a socket an
+app can open — receiving them needs `AF_PACKET` with `CAP_NET_RAW`, which is root. Shizuku does
+not bridge this either: the ADB shell user (uid 2000) has no `CAP_NET_RAW`, and stock devices do
+not ship `tcpdump`. Android's unprivileged ICMP sockets are what make `icmp.ping4` work without
+root; there is no equivalent back door for raw L2 receive.
+
+Worth building in the root module when it lands, because the payoff is large: LLDP names the
+switch, the port and the VLAN a device is attached to, which is the best available answer to
+"where in this building am I actually plugged in", and CDP does the same on Cisco gear. Until
+then they are recorded as absent capabilities rather than left to look unimplemented.
+
+What IS reachable at app tier, and what long mode now listens for instead: SSDP (passive NOTIFY
+plus periodic M-SEARCH), LLMNR, NetBIOS-NS and WS-Discovery — all IP multicast/broadcast, all
+sockets an app may open. The security reading matters as much as the inventory: LLMNR and
+NetBIOS-NS being live on a segment is a finding in itself, since both are trivially spoofable.
+
+**One of those four cannot run at app tier either, and says so.** `local.netbios_inventory`
+reports `unsupported` with the bind error attached: UDP 137 is below 1024, and Android reserves
+privileged ports exactly like any other Linux. The decoder, the evidence shape and the registry
+id are built and tested, waiting for the Shizuku tier to supply a socket. Recorded as a result
+rather than dropped, so nobody later reads its absence as an oversight.
+
+Two deliberate restraints in that work, both worth keeping: no active WS-Discovery Probe (an
+M-SEARCH is traffic every SSDP device expects constantly, whereas a WSD Probe from an unknown
+host announces *this* device to the segment), and no NBSTAT sweep (that is host scanning, not
+measurement — the app listens to what a network broadcasts, it does not interrogate its
+neighbours). The parsers are also hardened against the input they will actually meet: a DNS
+compression pointer is refused rather than followed (the classic parser hang), and the WSD
+extractor is string-based on purpose, tested against an entity bomb and 20 000-deep nesting.
+
+## Design note: what BLE between two devices is actually for (2026-08-02, not built)
+
+Two or more phones running Echolot, talking over Bluetooth LE. The schema already anticipates
+this — `Trigger.PEER` and the whole `peer.*` test family (`peer.reachability`, `peer.isolation`,
+`peer.multicast`, `peer.lan_train`, `peer.lease_diff`) are in the registry, unused — and the
+prober measured `peer.ble_advertise` **SUPPORTED on both known devices**, so the mechanism is
+proven; what has been missing is a reason that beats "use the server".
+
+**The reason is that BLE is out-of-band.** Everything else this app does depends on the network
+under test being at least partly functional. A second device reachable over a radio that shares
+nothing with the wifi turns several measurements from ambiguous into conclusive:
+
+1. **Client isolation becomes measurable at all.** Today, "I sent a packet to the peer and heard
+   nothing" cannot distinguish AP client isolation from the peer being asleep, gone, or on a
+   different VLAN — the failure mode is silence, and silence has too many parents. With BLE the
+   peer confirms out-of-band that it was listening on address X at time T, so silence over IP
+   becomes *proof* of isolation rather than a guess. This is the single strongest argument for
+   the feature, and it mirrors the rule this project keeps rediscovering: a measurement that
+   cannot separate "nothing happened" from "nothing was tried" is not a measurement.
+2. **Differential diagnosis: the network or this phone?** Two devices on the same SSID, one
+   resolving DNS and one not, settles in seconds what a single device cannot settle at all —
+   and it is the same distinction `system_verdict` exists to draw, only with a second opinion
+   instead of Android's. Natural finding: *this device fails where a peer on the same link
+   succeeds* → look at the device (private DNS, ad blocker, per-client router rule, MAC
+   randomization), not the router.
+3. **Two DHCP servers on one L2**, the classic invisible fault: peers compare lease source,
+   subnet and gateway (`peer.lease_diff`). Disagreement is conclusive and needs no server.
+4. **Coverage and roaming**, later: several devices sampling RSSI in different rooms, exchanging
+   summaries over BLE, gives a picture no single device standing in one place can produce.
+
+**What crosses the link is a summary, never the document.** A measurement document describes
+someone's home network in detail; broadcasting it to whoever is nearby would betray the whole
+posture of §8. The peer payload should be: a *hashed* network identity (so two devices can agree
+they are on the same L2 without either putting the SSID/BSSID on the air in the clear), the §7.3
+category verdicts, the finding codes, and an IP endpoint plus a one-shot nonce for the LAN tests.
+Findings and verdicts are already the interpretation layer — exactly the right granularity to
+share.
+
+**Privacy constraints, which are not optional here.** A BLE advertiser is a tracking beacon: it
+must be user-initiated, time-boxed to the run, carry no identifier that is stable across runs
+(the resolvable-private-address default plus a per-session ephemeral id), and pair by a code the
+two humans can see. "Discoverable by default" would make this app a worse citizen than the
+networks it audits.
+
+**Deliberately not doing:** clock synchronisation over BLE. GATT latency is jitter measured in
+tens of milliseconds, which is the same order as the one-way delays worth measuring; peers should
+sync against the server's `time.server_offset` and use BLE only to correlate run ids. Nor should
+BLE become a transport for uploads — it is a *comparison* channel.
+
+Staging when it happens: `peer.isolation` first (highest value, needs only advertise + connect +
+a nonce exchange), then `peer.lease_diff` (pure summary comparison, no extra plumbing), then the
+rest. Needs `BLUETOOTH_ADVERTISE/CONNECT/SCAN` in the manifest, which the app does not yet
+request.
+
+## v0.11.3 live on fmr; trains validated end to end (2026-08-02)
+
+Deployed via `--self-update` (the pre-signing v0.11.2 updater accepted the first signed release,
+as planned; every later update verifies). Startup clean on the real host — the reserved-port
+check passed against the OS, self-test green, capabilities unchanged plus the new machinery.
+
+**`train.udp_updown` validated against production**: `LiveUpstreamTrainTest` from this PC sent
+120 packets; the server's ledger counted 120, both columnar report parts arrived, loss 0.0 %,
+`truncated=false`. The 0x03/0x04/0x05 path works, client and server, over the real internet.
+
+Two operational bugs surfaced doing it:
+- **CLI-minted tokens are lost while the daemon runs.** `devices.json` is loaded once at startup
+  and held in memory; `--mint-enroll-token` writes to disk, the running daemon never re-reads,
+  answers "unknown token", and clobbers the token on its next write. `enroll-link.sh` has only
+  ever worked by timing luck. Workaround used: mint, `systemctl restart echolot-server`, then
+  redeem. Real fix belongs server-side (re-read on miss, or route the CLI mint through the
+  running daemon).
+- **`test-fmr.sh` still mints against `127.0.0.1:8444`**, which no longer exists (the admin API
+  moved to authenticated :443). Needs the same CLI-mint flow enroll-link.sh uses — plus the
+  restart caveat above until that bug is fixed.

docs/findings-registry.md

@@ -50,6 +50,13 @@ because it looks authoritative.
 | `connectivity.downstream_reorder` | low | Downstream packets arrive in a different order than they were sent. | — |
 | `connectivity.captive_portal` | medium | A captive portal is intercepting connectivity checks. | — |
 | `connectivity.no_internet` | high | Android's own connectivity checks fail on this network. | — |
+| `connectivity.link_flapping` | medium | A network dropped and came back one or more times during the run. | A momentary probe failure: the drop was watched happening, not inferred from silence. |
+
+`connectivity.link_flapping` is only reachable from a **long run** (`run.mode: "long"`,
+measurement-schema §3). It is derived from `networks[].changes[]` rather than from any test's
+evidence, because no one-shot probe can produce it: the probes before and after a four-second drop
+both succeed. The emitter escalates to *high* from three completed drop-and-return cycles, and
+requires the cycle to complete — a network switched off partway through a run is not flapping.
 
 ### mtu
 
@@ -89,9 +96,29 @@ rolled up under *connectivity* instead — the third occurrence of rule 1 being
 
 | code | severity | means | rules out |
 |---|---|---|---|
-| `v6.broken` | medium | IPv6 is configured on this network but does not work. | Absence of IPv6: it is provisioned, it simply fails. |
+| `dns.search_domain_unanswered` | high | The network advertises a DNS search domain that its own server does not answer for. | A fault on this device: the same server answers ordinary names normally. |
+| `dns.system_resolver_broken` | high | The network's DNS server answers, but this device cannot resolve names through it. | A network fault: the server replied to a query sent from this device. |
+| `measurement.vpn_constrained` | info | A VPN was active, so the networks underneath it could not be measured. | Nothing — this run says little about the underlying network either way. |
+| `v6.no_default_route` | medium | The device has a global IPv6 address but no IPv6 default route. | Guesswork: this is read from the routing table, not inferred from silence. |
+| `v6.route_without_address` | medium | The network advertises an IPv6 default route but the device has no global IPv6 address. | A working IPv6 setup: SLAAC did not produce a usable address on this link. |
+| `v6.no_icmp_reply` | low | IPv6 is configured but ICMPv6 echo gets no reply. | Nothing on its own: IPv6 may work fine with ICMP filtered. |
+| `v6.broken` | high | IPv6 is advertised on this network but carries no traffic. | ICMP filtering as the benign explanation: a TCP connection over IPv6 failed too. |
 | `v6.not_offered` | info | This network does not offer IPv6. | — |
 
+`v6.no_icmp_reply` was `v6.broken` until a phone reported it while loading an IPv6-only site over
+TCP perfectly well. The only evidence behind it is ICMPv6 echo, which is widely filtered on
+networks where IPv6 works — so the finding now states what was observed and names both
+explanations instead of choosing one. It is still worth reporting: filtered ICMPv6 breaks Path MTU
+Discovery.
+
+`v6.broken` returned once that corroboration existed: the `v6.brokenness` test attempts a real TCP
+connection over IPv6 to the configured server, and only when *both* transports fail on a network
+that advertises IPv6 is the brokenness claim made — at high severity, because every dual-stack
+destination pays a timeout before falling back to IPv4. When the TCP connect *succeeds*,
+`v6.no_icmp_reply` is emitted at high confidence instead, now able to say plainly that ICMPv6 is
+filtered while IPv6 works. With no server configured there is no corroboration target and the
+two-explanation `v6.no_icmp_reply` stands unchanged.
+
 `v6.not_offered` is **info and must stay info**. Most networks still do not offer IPv6 and that is
 not a fault; reporting it as a warning lights a yellow verdict on a healthy network, which teaches
 people to ignore the light — the one thing a diagnostic must never do.

docs/measurement-schema.md

@@ -38,6 +38,7 @@ Export encoding: UTF-8 JSON, gzip for files (`.echolot.json.gz`), share intent u
 {
   "id": "0198c5f2-...-uuidv7",
   "trigger": "manual | scheduled | monitor | peer",
+  "mode": "short | long",
   "started_at": "2026-07-29T14:03:21.114Z",
   "ended_at": "2026-07-29T14:07:44.902Z",
   "clock": {
@@ -52,12 +53,47 @@ Export encoding: UTF-8 JSON, gzip for files (`.echolot.json.gz`), share intent u
   },
   "tiers": { "app": true, "shizuku": true, "root": false },
   "profiles_used": ["profile-uuid", ...],
+  "constraints": {
+    "vpn_active": true,
+    "per_network_blocked": true,
+    "unmeasured_networks": ["net-0", "net-1"]
+  },
   "notes": "free-text user annotation"
 }
 ```
 
 `tiers` records what was *available*; each test records what it *used*.
 
+`mode` records how long the run watched, and it exists because **it changes what a reader may
+conclude from absence**. A `short` run is a sequence of one-shot probes — each looks at the network
+for a second or two and moves on — which characterises the network's *configuration* well and is
+structurally blind to anything intermittent. A `long` run starts continuous listeners at t=0, runs
+the same battery beside them, and keeps sampling until its window closes; the window's length is
+recorded in the `params` of the tests the listeners produce, not here.
+
+The consequence is asymmetric and matters more than the field looks. A finding is worth the same in
+either mode: a drop that was observed, was observed. Silence is not. "No link changes were seen" is
+evidence of a stable link after five minutes of watching and is evidence of nothing at all after a
+thirty-second run, in which a link could drop and return between two consecutive probes without
+leaving a mark anywhere in the document. Consumers — a diff between two runs, a dashboard counting
+how often a fault occurs, a person reading one report — must therefore not treat the absence of a
+time-dependent finding in a `short` run as its refutation, and must not compare the two modes as if
+they had asked the same question. `connectivity.link_flapping` is the first finding that only a
+`long` run can reach; `networks[].changes[]` (§4) is likewise populated only by a long run's
+listener, and an empty `changes[]` in a short run means "not watched", never "nothing happened".
+
+Absent `mode` means `short`: it was added after the first documents were written, and every one of
+them was a battery of one-shot probes.
+
+`constraints` records what was *prevented*. A constrained run is neither a failed run nor a normal
+one, and the distinction has to survive into the data: a run taken through a VPN has the same shape
+and the same green verdict as a clean run of a healthy network, so without this a reader — or a
+server aggregating thousands of them — cannot tell that almost nothing was measured. The known case
+is `per_network_blocked`: Android refuses `Network.bindSocket()` on the underlying networks while a
+VPN holds the default route, so every per-network test measures the tunnel or nothing at all, and
+any conclusion about the link underneath is unfounded. Consumers should treat findings from a
+constrained run as scoped to what was actually reachable, and `unmeasured_networks` names the rest.
+
 ## 4. `networks[]` — one entry per Android `Network` in play
 
 A run may exercise several networks simultaneously (Wi-Fi + cellular + USB ethernet). Everything is a snapshot at run start; a `changes[]` list captures mid-run deltas.
@@ -97,12 +133,24 @@ A run may exercise several networks simultaneously (Wi-Fi + cellular + USB ether
   "changes": [
     { "at_mono_ns": 91000000000, "kind": "lost | gained | link_changed",
       "detail": { /* new link snapshot or diff */ } }
-  ]
+  ],
+  "app_usable": true
 }
 ```
 
 `routes[].proto` and lifetime fields are Shizuku-tier data (`ip route`/`ip addr`); app-tier snapshots leave them absent — absence means "not observed", never "not present".
 
+`app_usable` records whether an ordinary app may send on this network at all. Android lists the
+carrier's special-purpose networks — IMS/VoLTE, MMS, XCAP — alongside the real ones, and they
+carry neither `INTERNET` nor `NOT_RESTRICTED`; binding to one needs
+`CONNECTIVITY_USE_RESTRICTED_NETWORKS`, which is signature-level and unobtainable for a normal
+app. Those networks are therefore permanently unmeasurable, and that is a property of Android's
+permission model rather than of the link. They stay in `networks[]` because they are genuinely
+present — an interface silently missing from the inventory is its own kind of lie — but a
+consumer must not read the absence of tests against them as a fault, and they are **not**
+`constraints.unmeasured_networks` (§3): nothing was prevented, the run was never entitled to
+measure them.
+
 ## 5. `server_sessions[]`
 
 ```json

docs/probe-protocol.md

@@ -84,7 +84,12 @@ The app re-fetches the profile at the start of every run (falling back to the ca
 
 ### 2.3 Capabilities (v1 registry)
 
-`udp-probe`, `stun-basic`, `stun-5780`, `canary-dns`, `recursive-dns`, `connect-back`, `delayed-echo`, `big-send`, `frag-send`, `tls-echo`, `http-echo`, `throughput`, `ntp`. A server omits what it can't offer (e.g. `stun-5780` without a second IP degrades to `stun-basic`). Clients must skip, and record as `unsupported`, any test whose capability is absent. Unknown capability strings are ignored.
+`udp-probe`, `stun-basic`, `stun-5780`, `canary-dns`, `recursive-dns`, `connect-back`, `delayed-echo`, `big-send`, `frag-send`, `tls-echo`, `http-echo`, `throughput`, `ntp`, plus:
+
+- `downtrain` — server-sent downstream trains via the §5 `downtrain` action. Upstream trains need no capability of their own: they are plain client-sent data-plane packets and ride `udp-probe`.
+- `tcp-echo` — the plain-TCP echo endpoint (§4); `tls-echo` is its ALPN variant on the same port.
+
+A server omits what it can't offer (e.g. `stun-5780` without a second IP degrades to `stun-basic`). Clients must skip, and record as `unsupported`, any test whose capability is absent. Unknown capability strings are ignored.
 
 ### 2.4 Sessions
 
@@ -111,6 +116,31 @@ DELETE /v1/sessions/{id}
 
 Per-credential and per-source-IP token buckets on: session creation, actions, UDP packets, bytes. `429` on control plane; silent drop on data plane (probes must tolerate loss anyway). All reflected/generated traffic goes **only** to the session's observed source address (or, for connect-back, the source address of the session-creating request). Data-plane responses to unauthenticated packets are never larger than the request (§3.4).
 
+### 2.2 `GET /v1/discover` — where the control plane lives
+
+Unauthenticated, and says almost nothing: the control-plane URL and the server's display name.
+
+```json
+{ "control_url": "https://probe.example.net", "name": "example" }
+```
+
+It exists so an enrollment link can carry the name a person recognises while the app still connects
+to the name that selects the pinned certificate. When a server shares port 443 between its admin UI
+and its control plane, those must be different hostnames — one port and one name is one certificate,
+and the two need different ones (a browser-trusted certificate, and a long-lived self-signed one the
+client pins). Without discovery, the difference leaks into every enrollment link an operator hands
+out.
+
+**It hands out an address, never a pin.** The pin travels in the link itself. Serving it here would
+reduce pinning to whatever the certificate authorities are worth, and pinning exists precisely to
+survive one the operator does not control — a root injected by corporate device management, for
+instance, which is unremarkable on the networks this tool is pointed at. Because the pin is
+pre-shared, an intercepted discovery response can only send a device to the wrong host, where the
+pin will not match: an outage, not a compromise.
+
+Clients treat it as optional. A server that does not answer, or a link that already names the
+control endpoint, works unchanged — enrollment must not begin failing because a lookup did.
+
 ## 3. UDP probe protocol
 
 ### 3.1 Packet header (fixed 32 bytes, network byte order)

echolot-app/app/build.gradle.kts

@@ -15,7 +15,7 @@ plugins {
 //
 // major*1_000_000 + minor*10_000 + patch*10 leaves room for 9 patch-level rebuilds (the trailing
 // digit) without disturbing the mapping, and stays inside the 2_100_000_000 ceiling until major 2100.
-val appVersionName = "0.2.0"
+val appVersionName = "0.3.0"
 
 fun versionCodeOf(semver: String): Int {
     val (major, minor, patch) = semver.substringBefore('-').split(".").map(String::toInt)
@@ -34,8 +34,16 @@ android {
         versionName = appVersionName
         // Automation: `adb shell am start -n app.echo_lot.app/.MainActivity --ez autorun true`
         // runs a measurement immediately and POSTs the report here (dev collection endpoint).
-        buildConfigField("String", "REPORT_UPLOAD_URL", "\"http://89.185.109.150:443/report\"")
-        buildConfigField("String", "REPORT_UPLOAD_SECRET", "\"D4OmG5gGJsElqVVbtYIZbR\"")
+        // Empty: the collection endpoint this pointed at was the adb-beacon receiver, which held
+        // 0.0.0.0:443 in cleartext. That service is gone and echolot-server owns 443 with TLS, so
+        // posting plaintext there now fails as "client sent an HTTP request to an HTTPS server" —
+        // an alarming error for a debugging convenience that is no longer needed, since autorun
+        // reports are read straight off the device with `run-as cat`.
+        //
+        // Deliberately not repointed at /v1/runs. That is the consent-gated upload, and a
+        // debugging shortcut must not be able to satisfy it by accident.
+        buildConfigField("String", "REPORT_UPLOAD_URL", "\"\"")
+        buildConfigField("String", "REPORT_UPLOAD_SECRET", "\"\"")
         // The bare SemVer, without the debug build's "-dev" suffix stripped away by the server's
         // parser anyway — sent to servers so they can apply their compatibility window.
         buildConfigField("String", "APP_SEMVER", "\"$appVersionName\"")

echolot-app/app/src/main/AndroidManifest.xml

@@ -10,6 +10,19 @@
     <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
     <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />
     <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
+    <!--
+      The adb relay (AdbRelayService) only. It runs in the foreground because it must keep
+      watching while the tablet sits unattended with its screen off, and dataSync is the type
+      that describes it: it carries an observation off the LAN, nothing more. Android 15 caps
+      dataSync at a few hours a day, which is acceptable for a tool that is switched on for a
+      debugging session rather than left running forever.
+    -->
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_DATA_SYNC" />
+    <!-- Only so the relay's ongoing status is visible; the service runs either way. -->
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
+    <!-- So the relay survives a reboot of a device left running it (see RelayBootReceiver). -->
+    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
 
     <application
         android:allowBackup="false"
@@ -22,7 +35,8 @@
 
         <activity
             android:name=".MainActivity"
-            android:exported="true">
+            android:exported="true"
+            android:launchMode="singleTask">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />
@@ -39,8 +53,41 @@
                 <category android:name="android.intent.category.BROWSABLE" />
                 <data android:scheme="echolot" android:host="enroll" />
             </intent-filter>
+            <!--
+              Sign-in redirect. The browser hands the authorization code back through this, which
+              is exactly why the flow uses PKCE: any app may register this scheme, so the code
+              alone must not be enough to complete a sign-in.
+            -->
+            <intent-filter android:autoVerify="false">
+                <action android:name="android.intent.action.VIEW" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <category android:name="android.intent.category.BROWSABLE" />
+                <data android:scheme="echolot" android:host="auth" />
+            </intent-filter>
         </activity>
 
+        <!--
+          Not exported: nothing outside this app has any business starting a relay that reports
+          where this device can be reached.
+        -->
+        <service
+            android:name=".AdbRelayService"
+            android:exported="false"
+            android:foregroundServiceType="dataSync" />
+
+        <!--
+          Exported because the system delivers these broadcasts; the receiver itself starts
+          nothing unless the relay was already switched on in a debug build.
+        -->
+        <receiver
+            android:name=".RelayBootReceiver"
+            android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.BOOT_COMPLETED" />
+                <action android:name="android.intent.action.MY_PACKAGE_REPLACED" />
+            </intent-filter>
+        </receiver>
+
         <provider
             android:name="androidx.core.content.FileProvider"
             android:authorities="${applicationId}.fileprovider"

echolot-app/app/src/main/kotlin/app/echo_lot/app/Account.kt

@@ -0,0 +1,125 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.app
+
+import app.echo_lot.protocol.AuthInfo
+import app.echo_lot.protocol.ControlClient
+import app.echo_lot.protocol.OidcLogin
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
+
+/**
+ * Signing in to the configured server's identity provider.
+ *
+ * The awkward part of a browser-based sign-in on Android is that the app is not running while it
+ * happens. Handing control to a browser puts this process in the background, where it may be
+ * killed at any moment; the callback then arrives at a fresh process with none of the state the
+ * exchange needs. So the PKCE verifier and state are written to storage before the browser opens,
+ * not held in memory — an in-memory value works on a developer's device and fails on a phone under
+ * memory pressure, which is the worst way for this to break.
+ *
+ * Nothing from the identity provider is kept afterwards. The ID token proves who is signing in,
+ * once; the device credential authenticates everything from then on.
+ */
+class Account(private val settings: Settings) {
+
+    private val json = Json { ignoreUnknownKeys = true }
+
+    sealed interface SignInStart {
+        /** Open this in a browser. */
+        data class Browser(val url: String) : SignInStart
+        data class Unavailable(val reason: String) : SignInStart
+    }
+
+    /** Fetches the server's auth configuration and builds the authorization URL. */
+    fun begin(): SignInStart {
+        if (!settings.serverConfigured) {
+            return SignInStart.Unavailable(
+                "Enrol with a server first — sign-in belongs to the server's identity provider."
+            )
+        }
+        val auth = runCatching { client().profile(settings.serverCredential).auth }.getOrNull()
+            ?: return SignInStart.Unavailable("Could not reach the server to ask how to sign in.")
+
+        auth.discoveryError?.let {
+            // The distinction matters: "the operator configured an IdP that is not answering" is
+            // their problem to fix, and is not the same as "this server has no accounts".
+            return SignInStart.Unavailable("The server's identity provider is not responding: $it")
+        }
+        if (!auth.enabled) {
+            return SignInStart.Unavailable("This server does not offer accounts.")
+        }
+        return try {
+            val pending = OidcLogin.begin(auth)
+            // Written before the browser opens, because after that this process may not survive.
+            settings.pendingVerifier = pending.verifier
+            settings.pendingState = pending.state
+            SignInStart.Browser(pending.authorizationUrl)
+        } catch (t: Throwable) {
+            SignInStart.Unavailable(t.message ?: "Could not start sign-in.")
+        }
+    }
+
+    /**
+     * Completes sign-in from the `echolot://auth` redirect.
+     *
+     * Blocking; callers run it off the main thread.
+     */
+    fun complete(callbackUri: String): String {
+        val verifier = settings.pendingVerifier
+        val state = settings.pendingState
+        // Cleared first, whatever happens next: these are single-use, and leaving them behind
+        // would let a later callback be completed against a flow nobody started.
+        settings.clearPendingAuth()
+
+        if (verifier.isBlank() || state.isBlank()) {
+            return "That sign-in did not start on this device."
+        }
+        return try {
+            val auth = client().profile(settings.serverCredential).auth
+            val idToken = OidcLogin.complete(
+                auth, OidcLogin.Pending("", verifier, state), callbackUri,
+            )
+            val reply = client().linkAccount(settings.serverCredential, idToken)
+            val o = json.parseToJsonElement(reply).jsonObject
+            val name = o["display_name"]?.jsonPrimitive?.content ?: "signed in"
+            settings.accountName = name
+            settings.accountId = o["account_id"]?.jsonPrimitive?.content ?: ""
+            val admin = o["admin"]?.jsonPrimitive?.content == "true"
+            "Signed in as $name" + if (admin) " (administrator)" else ""
+        } catch (e: OidcLogin.LoginFailed) {
+            e.message ?: "Sign-in failed."
+        } catch (t: Throwable) {
+            "Sign-in failed: ${t.message ?: t.javaClass.simpleName}"
+        }
+    }
+
+    /** Signs out. The device stays enrolled — signing out should not cost an enrolment. */
+    fun signOut(): String = try {
+        client().unlinkAccount(settings.serverCredential)
+        settings.accountName = ""
+        settings.accountId = ""
+        "Signed out. This device is still enrolled."
+    } catch (t: Throwable) {
+        "Could not sign out: ${t.message ?: t.javaClass.simpleName}"
+    }
+
+    /** Asks the server who it thinks is signed in, so the UI is not trusting stale local state. */
+    fun refresh(): String? = runCatching {
+        val o = json.parseToJsonElement(client().accountStatus(settings.serverCredential)).jsonObject
+        val signedIn = o["signed_in"]?.jsonPrimitive?.content == "true"
+        settings.accountName = if (signedIn) {
+            o["display_name"]?.jsonPrimitive?.content ?: ""
+        } else {
+            ""
+        }
+        settings.accountName.takeIf { it.isNotBlank() }
+    }.getOrNull()
+
+    private fun client() = ControlClient(
+        settings.serverUrl, setOf(settings.serverPin), BuildConfig.APP_SEMVER,
+        fallbackAddrs = settings.serverAddrList(),
+    )
+}

echolot-app/app/src/main/kotlin/app/echo_lot/app/AdbRelay.kt

@@ -0,0 +1,146 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.app
+
+import android.content.Context
+import android.net.ConnectivityManager
+import android.net.nsd.NsdManager
+import android.net.nsd.NsdServiceInfo
+import java.net.Inet4Address
+
+/**
+ * Watches adbd's own mDNS advertisement on this device and reports the endpoint to the server.
+ *
+ * This replaces the retired Python adb-beacon, and exists for one reason: **mDNS does not cross
+ * subnets**. A developer on another network cannot see `_adb-tls-connect._tcp` at all, while the
+ * wireless-debug port rotates every few minutes — so the port has to be carried out of the LAN by
+ * something sitting inside it. That is this. A tablet parked on the test network relays; the
+ * developer reads the endpoint back from the server.
+ *
+ * Two hard-won rules from the beacon, both load-bearing:
+ *
+ *  - **Resolve each service instance exactly ONCE.** Resolving adbd's advertisement makes adbd
+ *    re-arm its connection and post a "wireless debugging connected" notification; re-resolving on
+ *    every heartbeat turns that into a stream of them. The guard is cleared only when the service
+ *    is *lost*, which is also what catches rotation: the new advertisement is a new instance, gets
+ *    resolved once, and is reported within seconds.
+ *  - **Do not run this on the OnePlus.** On network churn that device drops and re-publishes its
+ *    advertisement repeatedly, so lost/found cycles keep clearing the guard and each resolve
+ *    re-arms adbd. Guarding reduces but cannot eliminate the noise; the Lenovo tablet is the
+ *    intended host, which is also why relaying is a mode rather than something always on.
+ */
+class AdbRelay(
+    private val ctx: Context,
+    private val onEvent: (String) -> Unit,
+) {
+    private val nsd = ctx.getSystemService(NsdManager::class.java)
+
+    /** Instances already resolved, by service name — the re-arm guard described above. */
+    private val resolved = HashSet<String>()
+
+    /** Last endpoint reported, so the heartbeat re-posts from cache instead of re-resolving. */
+    @Volatile var lastEndpoint: Endpoint? = null
+        private set
+
+    data class Endpoint(val host: String, val port: Int, val serviceName: String)
+
+    private var listener: NsdManager.DiscoveryListener? = null
+
+    fun start() {
+        if (nsd == null) {
+            onEvent("mDNS unavailable on this device")
+            return
+        }
+        if (listener != null) return
+        val l = object : NsdManager.DiscoveryListener {
+            override fun onStartDiscoveryFailed(type: String?, code: Int) {
+                onEvent("discovery failed to start (code $code)")
+            }
+            override fun onStopDiscoveryFailed(type: String?, code: Int) {}
+            override fun onDiscoveryStarted(type: String?) {
+                onEvent("watching for adbd on this network")
+            }
+            override fun onDiscoveryStopped(type: String?) {}
+
+            override fun onServiceFound(info: NsdServiceInfo?) {
+                val name = info?.serviceName ?: return
+                // The guard: one resolve per instance, ever. adbd re-arms on every resolve.
+                if (!resolved.add(name)) return
+                resolve(info)
+            }
+
+            override fun onServiceLost(info: NsdServiceInfo?) {
+                // Rotation: the old instance is gone, so allow the replacement to be resolved.
+                info?.serviceName?.let { resolved.remove(it) }
+            }
+        }
+        listener = l
+        runCatching { nsd.discoverServices(ADB_SERVICE, NsdManager.PROTOCOL_DNS_SD, l) }
+            .onFailure { onEvent("could not start discovery: ${it.message}") }
+    }
+
+    fun stop() {
+        listener?.let { l -> runCatching { nsd?.stopServiceDiscovery(l) } }
+        listener = null
+        resolved.clear()
+    }
+
+    @Suppress("DEPRECATION") // the callback-based resolve is the one that exists across our minSdk
+    private fun resolve(info: NsdServiceInfo) {
+        val cb = object : NsdManager.ResolveListener {
+            override fun onResolveFailed(i: NsdServiceInfo?, code: Int) {
+                // Let a failed instance be retried: the guard exists to stop *successful*
+                // re-resolution, not to give up on a transient failure.
+                i?.serviceName?.let { resolved.remove(it) }
+                onEvent("resolve failed (code $code)")
+            }
+
+            override fun onServiceResolved(i: NsdServiceInfo?) {
+                val host = i?.host?.hostAddress ?: return
+                // adbd advertises on every address it listens on, including link-local v6. The
+                // reachable one from a developer's subnet is the routable v4 address, and it is
+                // also the only one worth relaying — a link-local address means nothing off-link.
+                if (i.host !is Inet4Address) return
+                // Prefer this device's own advertisement: on a shared network several phones may
+                // have wireless debugging on, and relaying a neighbour's port would send a
+                // developer to the wrong device. But when this device cannot say what its own
+                // address is, that is no reason to relay nothing — an unverified endpoint beats
+                // silence, and it is labelled so it is never mistaken for a confirmed one.
+                val mine = localIp()
+                if (mine != null && host != mine) return
+                lastEndpoint = Endpoint(host, i.port, i.serviceName ?: "adb")
+                onEvent(
+                    if (mine == null) "found adbd at $host:${i.port} (own address unknown)"
+                    else "found adbd at $host:${i.port}"
+                )
+            }
+        }
+        runCatching { nsd?.resolveService(info, cb) }
+            .onFailure {
+                resolved.remove(info.serviceName)
+                onEvent("resolve threw: ${it.message}")
+            }
+    }
+
+    /**
+     * This device's own IPv4 address on the network it is relaying from, or null if it cannot be
+     * determined.
+     *
+     * Read from LinkProperties rather than `WifiManager.connectionInfo.ipAddress`, which is
+     * deprecated and returns 0 to ordinary apps on current Android — a null that silently made the
+     * ownership check reject every advertisement, so the relay found nothing and said nothing.
+     */
+    private fun localIp(): String? = runCatching {
+        val cm = ctx.getSystemService(ConnectivityManager::class.java) ?: return null
+        val lp = cm.getLinkProperties(cm.activeNetwork) ?: return null
+        lp.linkAddresses.map { it.address }
+            .filterIsInstance<Inet4Address>()
+            .firstOrNull { !it.isLoopbackAddress }
+            ?.hostAddress
+    }.getOrNull()
+
+    private companion object {
+        const val ADB_SERVICE = "_adb-tls-connect._tcp"
+    }
+}

echolot-app/app/src/main/kotlin/app/echo_lot/app/AdbRelayService.kt

@@ -0,0 +1,165 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.app
+
+import android.app.Notification
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.app.Service
+import android.content.Context
+import android.content.Intent
+import android.os.Build
+import android.os.IBinder
+import app.echo_lot.protocol.ControlClient
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.cancel
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+
+/**
+ * Keeps [AdbRelay] running and posts what it finds to the enrolled server.
+ *
+ * A foreground service because the whole point is to be useful while nobody is looking at the
+ * tablet: a background process is frozen within minutes of the screen going off, and a relay that
+ * stops relaying the moment it is left alone would be worse than none — it would be trusted right
+ * up until the moment it went quiet.
+ *
+ * The heartbeat re-posts the CACHED endpoint and never re-resolves. Resolving adbd's advertisement
+ * makes adbd re-arm its connection and raise a "wireless debugging connected" notification, so a
+ * heartbeat that re-resolved would turn a background convenience into a stream of notifications on
+ * a device sitting on a shelf. Rotation is still caught, because losing the old advertisement
+ * clears the resolve guard in [AdbRelay] and the replacement is resolved once, within seconds.
+ */
+class AdbRelayService : Service() {
+
+    private val scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+    private var relay: AdbRelay? = null
+
+    @Volatile private var status: String = "starting"
+    @Volatile private var lastPosted: String? = null
+
+    override fun onBind(intent: Intent?): IBinder? = null
+
+    override fun onCreate() {
+        super.onCreate()
+        startForeground(NOTIFICATION_ID, notification("starting"))
+        val settings = Settings(this)
+        val r = AdbRelay(this) { msg ->
+            status = msg
+            notify(msg)
+        }
+        relay = r
+        r.start()
+
+        scope.launch {
+            // Poll quickly until the first endpoint has actually been reported, then settle into
+            // the heartbeat. Discovery takes a few seconds, so a loop that only ever waited the
+            // heartbeat would see nothing on its first pass and then sit silent for two minutes —
+            // exactly when someone has just switched the relay on and is watching for it to work.
+            var reportedOnce = false
+            while (true) {
+                val ep = r.lastEndpoint
+                if (ep != null) {
+                    val wire = "${ep.host}:${ep.port}"
+                    // Re-post on a heartbeat even when unchanged: the server stamps a received-at
+                    // time, and a developer needs to tell "this endpoint is current" from "this
+                    // endpoint is what the tablet saw before it went out of range".
+                    val result = post(settings, ep)
+                    status = if (result == null) {
+                        lastPosted = wire
+                        reportedOnce = true
+                        "reported $wire"
+                    } else {
+                        "found $wire, but reporting failed: $result"
+                    }
+                    notify(status)
+                }
+                delay(if (reportedOnce) HEARTBEAT_MS else STARTUP_POLL_MS)
+            }
+        }
+    }
+
+    /** Posts one endpoint; returns null on success or a short reason on failure. */
+    private suspend fun post(settings: Settings, ep: AdbRelay.Endpoint): String? =
+        withContext(Dispatchers.IO) {
+            if (!settings.serverConfigured) return@withContext "no server enrolled"
+            runCatching {
+                ControlClient(settings.serverUrl, setOf(settings.serverPin), BuildConfig.APP_SEMVER)
+                    .reportAdbEndpoint(
+                        credential = settings.serverCredential,
+                        host = ep.host,
+                        port = ep.port,
+                        deviceName = Build.MODEL,
+                        note = "echolot relay",
+                    )
+                null
+            }.getOrElse { it.message?.take(120) ?: it.javaClass.simpleName }
+        }
+
+    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
+        // Restarted by the system if it is killed: a relay that quietly does not come back after
+        // a low-memory kill is the failure mode this exists to avoid.
+        return START_STICKY
+    }
+
+    override fun onDestroy() {
+        relay?.stop()
+        scope.cancel()
+        super.onDestroy()
+    }
+
+    private fun notify(text: String) {
+        val nm = getSystemService(NotificationManager::class.java)
+        nm?.notify(NOTIFICATION_ID, notification(text))
+    }
+
+    private fun notification(text: String): Notification {
+        val nm = getSystemService(NotificationManager::class.java)
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            // LOW: this is a status line for a tool the user deliberately started, not news.
+            val ch = NotificationChannel(CHANNEL, "adb relay", NotificationManager.IMPORTANCE_LOW)
+            ch.description = "Reports this device's wireless-debug endpoint to the Echolot server"
+            nm?.createNotificationChannel(ch)
+        }
+        val open = android.app.PendingIntent.getActivity(
+            this, 0, Intent(this, MainActivity::class.java),
+            android.app.PendingIntent.FLAG_IMMUTABLE,
+        )
+        return Notification.Builder(this, CHANNEL)
+            .setContentTitle("Echolot adb relay")
+            .setContentText(text)
+            .setSmallIcon(android.R.drawable.stat_sys_download_done)
+            .setOngoing(true)
+            .setContentIntent(open)
+            .build()
+    }
+
+    companion object {
+        private const val CHANNEL = "adb-relay"
+        private const val NOTIFICATION_ID = 4711
+
+        /**
+         * Two minutes. The port rotates on roughly that cadence, and the freshness of the answer
+         * is the whole product — but this only re-posts a cached value, so it costs one small
+         * HTTPS request and never touches mDNS.
+         */
+        private const val HEARTBEAT_MS = 120_000L
+
+        /** Retry cadence before the first successful report; cheap, and only ever runs at start. */
+        private const val STARTUP_POLL_MS = 5_000L
+
+        fun start(ctx: Context) {
+            val i = Intent(ctx, AdbRelayService::class.java)
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) ctx.startForegroundService(i)
+            else ctx.startService(i)
+        }
+
+        fun stop(ctx: Context) {
+            ctx.stopService(Intent(ctx, AdbRelayService::class.java))
+        }
+    }
+}

echolot-app/app/src/main/kotlin/app/echo_lot/app/MainActivity.kt

@@ -43,9 +43,28 @@ class MainActivity : ComponentActivity() {
     private val permissionLauncher =
         registerForActivityResult(ActivityResultContracts.RequestMultiplePermissions()) { /* proceed regardless */ }
 
+    /**
+     * The intent currently being acted on, so a deep link that arrives while the app is running
+     * is seen by the screen the user is already looking at.
+     *
+     * The activity is singleTask for the same reason. As a standard activity it stacked a second
+     * instance per link, each with its own ViewModel: the enrolment then happened in a throwaway
+     * copy, and pressing back returned to the original screen showing none of it. Silent, and
+     * indistinguishable from the link simply not working.
+     */
+    private val liveIntent = mutableStateOf<android.content.Intent?>(null)
+
+    override fun onNewIntent(intent: android.content.Intent) {
+        super.onNewIntent(intent)
+        setIntent(intent)
+        liveIntent.value = intent
+    }
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         requestRuntimePermissions()
+        resumeRelayIfEnabled()
+        liveIntent.value = intent
         setContent {
             MaterialTheme(colorScheme = darkColorScheme()) {
                 Surface(color = MaterialTheme.colorScheme.background) {
@@ -54,6 +73,9 @@ class MainActivity : ComponentActivity() {
                     // there is no back stack to model beyond "return to the run screen".
                     var screen by remember { mutableStateOf(Screen.RUN) }
                     var preview by remember { mutableStateOf<String?>(null) }
+                    // Hoisted so the home-screen switch and the settings toggle cannot disagree
+                    // about whether the relay is on.
+                    var relayOn by remember { mutableStateOf(vm.settings.adbRelayEnabled) }
                     // Automation entry point:
                     //   adb shell am start -n app.echo_lot.app/.MainActivity --ez autorun true
                     // starts a run immediately and uploads the report, so an unattended
@@ -63,15 +85,105 @@ class MainActivity : ComponentActivity() {
                     // An echolot://enroll link (QR scan, or a link the operator sent) opens the
                     // app straight into settings with the enrollment already done, so the user
                     // sees the result rather than a form they still have to fill in.
-                    val enrollUri = intent?.takeIf { it.action == Intent.ACTION_VIEW }?.dataString
+                    // Both deep links land here. They are told apart by host, so a sign-in
+                    // redirect is never mistaken for an enrolment link — one spends a token, the
+                    // other completes an authorization, and confusing them would fail obscurely.
+                    val incoming = liveIntent.value?.takeIf { it.action == Intent.ACTION_VIEW }?.dataString
+                    val authUri = incoming?.takeIf { it.startsWith("echolot://auth") }
+                    val enrollUri = incoming?.takeIf { it.startsWith("echolot://enroll") }
                     androidx.compose.runtime.LaunchedEffect(enrollUri) {
                         if (enrollUri != null) {
                             vm.enroll(enrollUri)
                             screen = Screen.SETTINGS
                         }
                     }
+                    // Replacing an existing enrollment is asked about, never assumed. Following a
+                    // link from a web page is one tap, and the old credential does not survive it.
+                    vm.state.pendingEnroll?.let { pending ->
+                        androidx.compose.material3.AlertDialog(
+                            onDismissRequest = { vm.cancelEnroll() },
+                            title = {
+                                androidx.compose.material3.Text(
+                                    if (pending.sameServer) "Enroll again with this server?"
+                                    else "Replace this device's server?"
+                                )
+                            },
+                            text = {
+                                androidx.compose.material3.Text(
+                                    // Naming the same URL twice reads as a mistake and buries the
+                                    // one consequence that actually applies: the device is issued a
+                                    // fresh credential and shows up as a second entry.
+                                    if (pending.sameServer) {
+                                        "This device is already enrolled with " +
+                                            "${pending.currentServer}.\n\n" +
+                                            "Enrolling again replaces its credential. The old one " +
+                                            "stops working immediately, and the device appears on " +
+                                            "the server as a new entry alongside the current one — " +
+                                            "which you may want to revoke afterwards.\n\n" +
+                                            "Runs already uploaded, and runs stored on this phone, " +
+                                            "are not affected."
+                                    } else {
+                                        "This device is already enrolled with " +
+                                            "${pending.currentServer}.\n\n" +
+                                            "Enrolling with ${pending.newServer} replaces that. Runs " +
+                                            "already uploaded stay where they are, but this device " +
+                                            "stops reporting to the old server and appears on the new " +
+                                            "one as a new device.\n\n" +
+                                            "Runs stored on this phone are not affected."
+                                    }
+                                )
+                            },
+                            confirmButton = {
+                                androidx.compose.material3.TextButton(onClick = { vm.confirmEnroll() }) {
+                                    androidx.compose.material3.Text(
+                                        if (pending.sameServer) "Enroll again" else "Enroll here"
+                                    )
+                                }
+                            },
+                            dismissButton = {
+                                androidx.compose.material3.TextButton(onClick = { vm.cancelEnroll() }) {
+                                    androidx.compose.material3.Text("Keep current server")
+                                }
+                            },
+                        )
+                    }
+                    androidx.compose.runtime.LaunchedEffect(authUri) {
+                        if (authUri != null) {
+                            vm.completeSignIn(authUri)
+                            screen = Screen.SETTINGS
+                        }
+                    }
+                    // A long run samples for minutes, and Android starts throttling timers and
+                    // network access within moments of the screen going off — so a run left to
+                    // itself would measure the device's power management rather than the network,
+                    // and would do it silently. Held only while a run is in flight, and released
+                    // on the way out.
+                    val view = androidx.compose.ui.platform.LocalView.current
+                    androidx.compose.runtime.DisposableEffect(vm.state.running) {
+                        view.keepScreenOn = vm.state.running
+                        onDispose { view.keepScreenOn = false }
+                    }
+                    // Shizuku can be started, stopped or authorised in its own app, where nothing
+                    // calls back into this process. Asking again each time this screen comes
+                    // forward is what makes the banner right after the user has been away to fix
+                    // it — which is exactly the moment they look at it.
+                    val lifecycleOwner = androidx.compose.ui.platform.LocalLifecycleOwner.current
+                    androidx.compose.runtime.DisposableEffect(lifecycleOwner) {
+                        val obs = androidx.lifecycle.LifecycleEventObserver { _, event ->
+                            if (event == androidx.lifecycle.Lifecycle.Event.ON_RESUME) {
+                                vm.refreshShizuku()
+                            }
+                        }
+                        lifecycleOwner.lifecycle.addObserver(obs)
+                        onDispose { lifecycleOwner.lifecycle.removeObserver(obs) }
+                    }
+                    // Autorun stays a quick run: it is an unattended batch job driven over adb, and
+                    // an automation that silently held the device for five minutes would be a
+                    // surprise. `--es mode long` asks for the other one explicitly.
+                    val autorunMode =
+                        if (intent?.getStringExtra("mode") == "long") RunMode.LONG else RunMode.SHORT
                     androidx.compose.runtime.LaunchedEffect(autorun) {
-                        if (autorun) vm.run(devUpload = true)
+                        if (autorun) vm.run(autorunMode, devUpload = true)
                     }
                     // In autorun the app is a batch job: once the run is done AND the upload
                     // succeeded, show the result briefly, then close so the device is left as it
@@ -107,8 +219,25 @@ class MainActivity : ComponentActivity() {
                             lifecycleScope.launch { preview = vm.previewNewestRun() }
                         },
                         onCheckServer = vm::checkServer,
+                        accountName = vm.accountName,
+                        onSignIn = {
+                            vm.beginSignIn { url ->
+                                // A plain VIEW intent rather than a Custom Tab: the browser is
+                                // where the user's existing IdP session already lives, and
+                                // androidx.browser would be a dependency for a rounded corner.
+                                runCatching {
+                                    startActivity(Intent(Intent.ACTION_VIEW, android.net.Uri.parse(url)))
+                                }
+                            }
+                        },
+                        onSignOut = vm::signOut,
                         onEnroll = vm::enroll,
                         serverStatus = vm.state.archiveStatus,
+                        enrollStatus = vm.state.enrollStatus,
+                        onRelayChange = { on ->
+                            if (on) AdbRelayService.start(this@MainActivity)
+                            else AdbRelayService.stop(this@MainActivity)
+                        },
                         onBack = { screen = Screen.RUN },
                       )
                       Screen.HISTORY -> HistoryScreen(
@@ -132,7 +261,10 @@ class MainActivity : ComponentActivity() {
                       )
                       Screen.RUN -> EcholotScreen(
                         state = vm.state,
-                        onRun = { vm.run() },
+                        longMinutes = vm.settings.longRunMinutes,
+                        discoveryEnabled = { vm.settings.discoveryEnabled(it) },
+                        onDiscoveryChange = { id, on -> vm.settings.setDiscoveryEnabled(id, on) },
+                        onRun = { mode -> vm.run(mode) },
                         onCancel = vm::cancel,
                         onDeveloperOptions = {
                             runCatching {
@@ -154,6 +286,19 @@ class MainActivity : ComponentActivity() {
                                 else -> Unit
                             }
                         },
+                        relayOn = relayOn,
+                        // Dev builds only. The relay publishes where this device can be reached
+                        // over adb; that is scaffolding for driving a test device, and a release
+                        // build has no business offering it — it would be useless without
+                        // wireless debugging and a footgun for anyone who switched it on without
+                        // knowing what it announces.
+                        relayAvailable = BuildConfig.DEBUG && vm.settings.serverConfigured,
+                        onRelayToggle = { on ->
+                            relayOn = on
+                            vm.settings.adbRelayEnabled = on
+                            if (on) AdbRelayService.start(this@MainActivity)
+                            else AdbRelayService.stop(this@MainActivity)
+                        },
                         onExport = { doc -> startActivity(Intent.createChooser(Report.share(this, doc), "Export Echolot run")) },
                         onOpenSettings = { screen = Screen.SETTINGS },
                         onOpenHistory = { vm.refreshHistory(); screen = Screen.HISTORY },
@@ -169,11 +314,29 @@ class MainActivity : ComponentActivity() {
 
     private fun requestRuntimePermissions() {
         val perms = mutableListOf(Manifest.permission.ACCESS_FINE_LOCATION)
+        // Only so the relay's ongoing notification is visible. The service runs either way, but a
+        // foreground service the user cannot see is worse than one they can dismiss knowingly.
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
+            perms.add(Manifest.permission.POST_NOTIFICATIONS)
+        }
         val missing = perms.filter {
             ContextCompat.checkSelfPermission(this, it) != PackageManager.PERMISSION_GRANTED
         }
         if (missing.isNotEmpty()) permissionLauncher.launch(missing.toTypedArray())
     }
+
+    /**
+     * Restarts the relay if it was left on.
+     *
+     * A relay that silently fails to come back after a reboot or a process kill is worse than one
+     * that was never enabled: it is trusted right up to the moment it goes quiet, and the symptom
+     * is a stale endpoint that sends a developer to a port nothing is listening on.
+     */
+    private fun resumeRelayIfEnabled() {
+        if (Settings(this).adbRelayEnabled) {
+            runCatching { AdbRelayService.start(this) }
+        }
+    }
 }
 
 private fun verdictColor(v: Verdict): Color = when (v) {
@@ -191,9 +354,20 @@ private fun statusColor(s: TestStatus): Color = when (s) {
 }
 
 @Composable
+// FlowRow: the discovery chips wrap rather than overflow on a narrow phone. Experimental only in
+// the sense that its API may gain parameters; the layout itself has been stable for releases.
+@OptIn(ExperimentalLayoutApi::class)
 private fun EcholotScreen(
     state: UiState,
-    onRun: () -> Unit,
+    longMinutes: Int,
+    /** Which discovery listeners are selected, and how to change one. */
+    discoveryEnabled: (String) -> Boolean,
+    onDiscoveryChange: (String, Boolean) -> Unit,
+    /** The relay is not a run mode, but it is switched on from here because that is where it is looked for. */
+    relayOn: Boolean,
+    relayAvailable: Boolean,
+    onRelayToggle: (Boolean) -> Unit,
+    onRun: (RunMode) -> Unit,
     onCancel: () -> Unit,
     onShizukuAction: () -> Unit,
     onDeveloperOptions: () -> Unit,
@@ -257,8 +431,106 @@ private fun EcholotScreen(
             }
         }
 
+        // The choice is made before the run, not after, because it is a choice about how long the
+        // user is willing to stand still — and because the two modes answer different questions.
+        var mode by remember { mutableStateOf(RunMode.SHORT) }
+        Row(horizontalArrangement = Arrangement.spacedBy(8.dp), verticalAlignment = Alignment.CenterVertically) {
+            FilterChip(
+                selected = mode == RunMode.SHORT,
+                onClick = { mode = RunMode.SHORT },
+                enabled = !state.running,
+                label = { Text("Quick") },
+            )
+            FilterChip(
+                selected = mode == RunMode.LONG,
+                onClick = { mode = RunMode.LONG },
+                enabled = !state.running,
+                label = { Text("Long ($longMinutes min)") },
+            )
+        }
+        Text(
+            if (mode == RunMode.SHORT) {
+                "About 30 seconds. Describes how the network is configured right now."
+            } else {
+                "Listens for $longMinutes minutes while it measures. Finds what a quick run " +
+                    "structurally cannot: links that drop and come back, signal that decays, " +
+                    "loss that arrives in bursts."
+            },
+            fontSize = 12.sp, color = MaterialTheme.colorScheme.onSurfaceVariant,
+        )
+
+        // Discovery listeners, chosen the same way as the mode and only where they mean anything.
+        // They belong to the window: a passive listener in a quick run would mostly hear silence
+        // and report an empty network as confidently as a quiet one.
+        if (mode == RunMode.LONG) {
+            var discovery by remember {
+                mutableStateOf(DiscoveryIds.ALL.filter(discoveryEnabled).toSet())
+            }
+            Text(
+                "Also listen for",
+                fontSize = 12.sp, fontWeight = FontWeight.Medium,
+                modifier = Modifier.padding(top = 4.dp),
+            )
+            FlowRow(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                for (id in DiscoveryIds.ALL) {
+                    val on = id in discovery
+                    FilterChip(
+                        selected = on,
+                        onClick = {
+                            val next = !on
+                            onDiscoveryChange(id, next)
+                            discovery = if (next) discovery + id else discovery - id
+                        },
+                        enabled = !state.running,
+                        label = { Text(DiscoveryIds.label(id)) },
+                    )
+                }
+            }
+            Text(
+                discovery.joinToString("  ·  ") { DiscoveryIds.blurb(it) }
+                    .ifBlank { "Nothing extra — just the measurements above." },
+                fontSize = 11.sp, color = MaterialTheme.colorScheme.onSurfaceVariant,
+            )
+        }
+
+        // Deliberately NOT a third chip beside Quick and Long. Those choose how the next run
+        // measures; this starts a service that keeps running afterwards and produces no document
+        // at all, so putting it in the same row would promise that "Run measurement" starts it.
+        // It lives here anyway because here is where it gets looked for.
+        var relay by remember { mutableStateOf(relayOn) }
+        if (relayAvailable || relay) Card(Modifier.fillMaxWidth()) {
+            Row(
+                Modifier.fillMaxWidth().padding(horizontal = 12.dp, vertical = 8.dp),
+                verticalAlignment = Alignment.CenterVertically,
+            ) {
+                Column(Modifier.weight(1f)) {
+                    Text(
+                        "Relay adb endpoint" + if (relay) " — on" else "",
+                        fontSize = 13.sp, fontWeight = FontWeight.Medium,
+                        color = LocalContentColor.current.copy(alpha = if (relayAvailable) 1f else 0.5f),
+                    )
+                    Text(
+                        if (!relayAvailable) {
+                            "Needs an enrolled server."
+                        } else if (relay) {
+                            "Reporting this device's wireless-debug host:port to the server."
+                        } else {
+                            "Not a measurement: lets a developer on another network find this " +
+                                "device when the port rotates."
+                        },
+                        fontSize = 11.sp, color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    )
+                }
+                Switch(
+                    checked = relay,
+                    enabled = relayAvailable,
+                    onCheckedChange = { on -> relay = on; onRelayToggle(on) },
+                )
+            }
+        }
+
         Row(horizontalArrangement = Arrangement.spacedBy(12.dp), verticalAlignment = Alignment.CenterVertically) {
-            Button(onClick = onRun, enabled = !state.running) {
+            Button(onClick = { onRun(mode) }, enabled = !state.running) {
                 Text(if (state.running) "Running…" else "Run measurement")
             }
             if (state.running) {
@@ -279,25 +551,55 @@ private fun EcholotScreen(
 
         if (state.running) {
             Column(verticalArrangement = Arrangement.spacedBy(6.dp)) {
-                val frac = if (state.stepsTotal > 0)
-                    state.stepsDone.toFloat() / state.stepsTotal else 0f
+                // In a long run the window is the run: once the battery is done, four minutes of
+                // listening remain, and a bar driven by the step count would sit at 100 % through
+                // all of it — which reads as an app that has hung, not one that is working.
+                val listening = state.windowTotalS > 0
+                val frac = when {
+                    listening -> state.windowElapsedS.toFloat() / state.windowTotalS
+                    state.stepsTotal > 0 -> state.stepsDone.toFloat() / state.stepsTotal
+                    else -> 0f
+                }
                 LinearProgressIndicator(
-                    progress = { frac },
+                    progress = { frac.coerceIn(0f, 1f) },
                     modifier = Modifier.fillMaxWidth(),
                 )
+                if (listening) {
                     Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                        Text(
+                            "listening ${clock(state.windowElapsedS)} of ${clock(state.windowTotalS)}",
+                            fontSize = 12.sp, fontWeight = FontWeight.Medium,
+                        )
+                        Text(
+                            "${clock(state.windowTotalS - state.windowElapsedS)} left",
+                            fontSize = 12.sp, modifier = Modifier.weight(1f),
+                            color = MaterialTheme.colorScheme.onSurfaceVariant,
+                        )
+                    }
+                }
+                Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                    // Still shown during a long run's listening phase, where it stops at the last
+                    // test: the battery's progress is real information, it is simply not the whole
+                    // run any more.
                     Text(
                         if (state.stepsTotal > 0)
-                            "test ${state.stepsDone + 1} of ${state.stepsTotal}" else "starting",
+                            "test ${(state.stepsDone + 1).coerceAtMost(state.stepsTotal)} of ${state.stepsTotal}"
+                        else "starting",
                         fontSize = 12.sp, fontWeight = FontWeight.Medium,
                     )
                     Text(state.currentStep ?: "…", fontSize = 12.sp,
                         fontFamily = FontFamily.Monospace, modifier = Modifier.weight(1f))
-                    if (state.etaSeconds > 0) {
+                    if (!listening && state.etaSeconds > 0) {
                         Text("~${state.etaSeconds}s left", fontSize = 12.sp,
                             color = MaterialTheme.colorScheme.onSurfaceVariant)
                     }
                 }
+                if (listening) {
+                    Text(
+                        "Cancelling keeps what has been collected so far.",
+                        fontSize = 11.sp, color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    )
+                }
             }
         }
 
@@ -307,11 +609,57 @@ private fun EcholotScreen(
 
 @Composable
 private fun Results(doc: MeasurementDocument) {
+    // A constrained run is answered before the lights are: the verdict below is INCONCLUSIVE by
+    // §7.3, and without this banner "inconclusive" reads as the app failing rather than the OS
+    // (correctly) refusing to let anything past the VPN be measured.
+    val constraints = doc.run.constraints
+    if (constraints.constrained) {
+        val blocked = constraints.unmeasuredNetworks
+            .mapNotNull { id -> doc.networks.firstOrNull { it.id == id } }
+            .joinToString(", ") { it.iface?.takeIf { s -> s.isNotBlank() } ?: it.transport.name.lowercase() }
+            .ifBlank { "the networks beneath it" }
+        // Same three-way split as the finding: saying "VPN" when the user just disconnected
+        // theirs (the wall lingers during teardown) reads as the app being wrong, not the OS.
+        val (headline, body) = when {
+            constraints.vpnActive && constraints.perNetworkBlocked ->
+                "Measured through a VPN" to
+                    ("Android does not let apps send on the networks beneath an active VPN, so " +
+                        "$blocked could not be measured — these results describe the tunnel. " +
+                        "Disconnect the VPN and run again to measure the networks themselves.")
+            constraints.perNetworkBlocked ->
+                "Some networks could not be measured" to
+                    ("Android refused this app permission to send on $blocked, so they went " +
+                        "unmeasured. A connected VPN is the usual cause; the refusal can also " +
+                        "outlast one. Everything else in this run is unaffected.")
+            else ->
+                "A VPN holds the default route" to
+                    ("Default-route results describe the tunnel; per-network measurements " +
+                        "reached the underlying networks.")
+        }
+        Card(colors = CardDefaults.cardColors(containerColor = Color(0xFF3A2E12))) {
+            Column(Modifier.fillMaxWidth().padding(12.dp)) {
+                Text(headline, color = Color(0xFFFFD08A), fontWeight = FontWeight.SemiBold)
+                Text(body, fontSize = 12.sp, color = Color(0xFFFFD08A))
+            }
+        }
+    }
+
     val summary = doc.summary
     if (summary != null) {
         Card(colors = CardDefaults.cardColors(containerColor = verdictColor(summary.overall))) {
             Column(Modifier.fillMaxWidth().padding(16.dp)) {
                 Text("Overall: ${summary.overall}", color = Color.White, fontWeight = FontWeight.Bold, fontSize = 18.sp)
+                // Which question this document answers. A green light from a quick run does not
+                // mean the same thing as a green light from a long one, and the report should not
+                // let the two look identical.
+                Text(
+                    if (doc.run.mode == RunMode.LONG) {
+                        "long run — the network was watched continuously as well as probed"
+                    } else {
+                        "quick run — a snapshot; nothing here rules out an intermittent fault"
+                    },
+                    color = Color.White, fontSize = 12.sp,
+                )
             }
         }
         FlowCategories(summary.categories)
@@ -417,6 +765,12 @@ private fun FlowCategories(categories: Map<String, CategorySummary>) {
     }
 }
 
+/** m:ss — minutes are how a five-minute wait is read; "247s left" is a number to convert. */
+private fun clock(seconds: Int): String {
+    val s = seconds.coerceAtLeast(0)
+    return "${s / 60}:${"%02d".format(s % 60)}"
+}
+
 @Composable
 private fun Dot(color: Color) {
     Surface(color = color, shape = RoundedCornerShape(50), modifier = Modifier.size(12.dp)) {}

echolot-app/app/src/main/kotlin/app/echo_lot/app/RelayBootReceiver.kt

@@ -0,0 +1,33 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.app
+
+import android.content.BroadcastReceiver
+import android.content.Context
+import android.content.Intent
+
+/**
+ * Brings the relay back after a reboot or an app update, without anyone opening the app.
+ *
+ * The relay's whole purpose is to keep answering "where is this device" while the device sits on a
+ * shelf unattended. Starting it only from [MainActivity] meant it silently did not come back from
+ * either event — and a relay that has quietly stopped is worse than one that was never switched
+ * on, because the endpoint it last published keeps looking authoritative while pointing at a port
+ * nothing is listening on.
+ *
+ * `MY_PACKAGE_REPLACED` matters as much as boot here: installing a new build is the single most
+ * common way this service dies during development, which is exactly when it is being relied on.
+ */
+class RelayBootReceiver : BroadcastReceiver() {
+    override fun onReceive(ctx: Context, intent: Intent) {
+        if (!BuildConfig.DEBUG) return
+        when (intent.action) {
+            Intent.ACTION_BOOT_COMPLETED, Intent.ACTION_MY_PACKAGE_REPLACED -> {
+                if (Settings(ctx).adbRelayEnabled) {
+                    runCatching { AdbRelayService.start(ctx) }
+                }
+            }
+        }
+    }
+}

echolot-app/app/src/main/kotlin/app/echo_lot/app/RunStore.kt

@@ -80,8 +80,16 @@ class RunStore(context: Context, private val settings: Settings) {
 
     private fun client() = ControlClient(
         settings.serverUrl, setOf(settings.serverPin), BuildConfig.APP_SEMVER,
+        fallbackAddrs = settings.serverAddrList(),
     )
 
+    /** Remembers where the server lives, so a later run can reach it without DNS. */
+    private fun rememberAddrs(p: app.echo_lot.protocol.Profile) {
+        val addrs = p.targets.flatMap { listOfNotNull(it.ip4, it.ip6) }
+            .filter { it.isNotBlank() }
+        if (addrs.isNotEmpty()) settings.serverAddrs = addrs.joinToString(",")
+    }
+
     /**
      * Checks the configured server without uploading anything: reachable, pinned, compatible, and
      * willing to accept runs. Lets the user find out in settings rather than from a failed run.
@@ -90,6 +98,10 @@ class RunStore(context: Context, private val settings: Settings) {
         if (!settings.serverConfigured) return "Fill in the server URL, pin and credential first."
         return try {
             val profile = client().profile(settings.serverCredential)
+            // Learned here so the next run's canary probe knows what to ask for.
+            profile.canaryZone.takeIf { it.isNotBlank() }?.let { settings.canaryZone = it }
+            settings.serverFacts = describeFacts(profile)
+            rememberAddrs(profile)
             val compat = Compat.check(profile, BuildConfig.APP_SEMVER)
             val head = "${profile.name} · server ${profile.serverVersion} · " +
                 "protocol ${profile.compat.protocolVersion.ifBlank { "unstated" }}"
@@ -115,6 +127,36 @@ class RunStore(context: Context, private val settings: Settings) {
      * no credential — fails later, somewhere else, with an error that points at the wrong thing.
      * Blocking; callers run it off the main thread.
      */
+
+    /**
+     * Renders what the server says about itself, for display.
+     *
+     * Only what a person measuring against it would want to check: which addresses the tests will
+     * actually use, on which ports, and what the server admits it can do. Addresses first, because
+     * "which address did this result come from" is the question a report leaves open.
+     */
+    private fun describeFacts(p: app.echo_lot.protocol.Profile): String {
+        val lines = ArrayList<String>()
+        // "label|value" per line, laid out as real columns by the UI rather than padded with
+        // spaces here. Space padding only lines up in a monospaced font, which makes the layout
+        // depend on a typeface choice made somewhere else entirely.
+        fun row(label: String, value: String) = lines.add("$label|$value")
+
+        row("server", "${p.name} · ${p.serverVersion}")
+        for (t in p.targets) {
+            t.ip4?.let { row("IPv4", it) }
+            t.ip6?.let { row("IPv6", it) }
+            // Marked rather than listed apart: it is the same server, and what matters is being
+            // able to tell which address a NAT-behaviour result came from.
+            t.ip4Alt?.let { row("IPv4 alt", it) }
+            t.ip6Alt?.let { row("IPv6 alt", it) }
+            row("ports", "udp ${t.udpPort} · tcp ${t.tcpPort} · stun ${t.stunPort}")
+        }
+        if (p.canaryZone.isNotBlank()) row("dns zone", p.canaryZone)
+        if (p.capabilities.isNotEmpty()) row("measures", p.capabilities.joinToString(", "))
+        return lines.joinToString(System.lineSeparator())
+    }
+
     fun enroll(link: String, deviceName: String?): String {
         val parsed = app.echo_lot.protocol.EnrollmentLink.parse(link)
             ?: return "That does not look like an Echolot enrollment link. It should start with " +
@@ -122,7 +164,11 @@ class RunStore(context: Context, private val settings: Settings) {
         return try {
             val enrolled = parsed.redeem(deviceName, BuildConfig.APP_SEMVER)
             val compat = Compat.check(enrolled.profile, BuildConfig.APP_SEMVER)
+            settings.serverFacts = describeFacts(enrolled.profile)
+            rememberAddrs(enrolled.profile)
+            enrolled.profile.canaryZone.takeIf { it.isNotBlank() }?.let { settings.canaryZone = it }
             settings.serverUrl = enrolled.controlUrl
+            settings.serverPublicUrl = enrolled.publicUrl
             settings.serverPin = enrolled.pin
             settings.serverCredential = enrolled.credential
             val head = "Enrolled with ${enrolled.profile.name} " +
@@ -150,6 +196,9 @@ class RunStore(context: Context, private val settings: Settings) {
         return try {
             val client = client()
             val profile = client.profile(settings.serverCredential)
+            profile.canaryZone.takeIf { it.isNotBlank() }?.let { settings.canaryZone = it }
+            settings.serverFacts = describeFacts(profile)
+            rememberAddrs(profile)
 
             // Compatibility before policy: an incompatible server may well advertise an upload
             // policy it would never actually apply to us.

echolot-app/app/src/main/kotlin/app/echo_lot/app/RunViewModel.kt

@@ -23,6 +23,8 @@ import app.echo_lot.probe.RouterIdentityProbe
 import app.echo_lot.shizuku.ShizukuAvailability
 import app.echo_lot.shizuku.ShizukuProbe
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.isActive
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
 import java.time.Instant
@@ -38,10 +40,32 @@ data class UiState(
     val stepsDone: Int = 0,
     val stepsTotal: Int = 0,
     val etaSeconds: Int = 0,
+    /** Which mode the run in progress (or the last one) used. */
+    val mode: RunMode = RunMode.SHORT,
+    /**
+     * The listening window, in seconds. Zero for a short run.
+     *
+     * A long run's step count stops being the honest progress measure the moment the battery is
+     * done and four minutes of listening remain: the bar would sit at 100 % while the run carried
+     * on, which reads as a hung app. Over a window, elapsed-of-total is the truth.
+     */
+    val windowElapsedS: Int = 0,
+    val windowTotalS: Int = 0,
     /** Where the finished run went: archived locally, uploaded, or neither (and why). */
     val archiveStatus: String? = null,
     /** History, newest first. Refreshed after every run and whenever the history screen opens. */
     val history: List<app.echo_lot.archive.ArchivedRun> = emptyList(),
+    /**
+     * Result of the last enrollment attempt, shown beside the Enroll button.
+     *
+     * Separate from [archiveStatus]: they are two different actions with two different results,
+     * and sharing one line put the answer to "did enrolling work" at the far end of the card,
+     * below three text fields — or nowhere at all on a fresh install, since that line only
+     * renders once a run exists.
+     */
+    val enrollStatus: String? = null,
+    /** An enrollment link waiting on confirmation, because this device is already enrolled. */
+    val pendingEnroll: PendingEnroll? = null,
     /** Shell-tier readiness, shown before a run; null message = say nothing (Shizuku not installed). */
     val shizukuNotice: String? = null,
     val shizukuReady: Boolean = false,
@@ -49,6 +73,18 @@ data class UiState(
     val shizukuState: ShizukuAvailability.State = ShizukuAvailability.State.NOT_INSTALLED,
 )
 
+/**
+ * An enrollment link that would replace an existing one, held until the user says so.
+ *
+ * Enrolling is not additive: the new credential replaces the old, and on the previous server this
+ * device simply stops reporting. Following a link is one tap from a web page, which is not enough
+ * deliberation to discard a working enrollment by accident.
+ */
+data class PendingEnroll(val link: String, val currentServer: String, val newServer: String) {
+    /** Re-enrolling with the server already configured, rather than moving to a different one. */
+    val sameServer: Boolean get() = currentServer.trimEnd('/') == newServer.trimEnd('/')
+}
+
 /**
  * Drives one measurement run: device-tier probes (link snapshot, per-network ICMP) always run;
  * results assemble into a MeasurementDocument with a §7.3 summary. Lives in a ViewModel so a run
@@ -80,8 +116,36 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
         }
     }
 
+    /**
+     * Re-reads the shell tier's state, for when it changed somewhere this process cannot see.
+     *
+     * Permission can be granted inside Shizuku's own app, and Shizuku can be started or stopped
+     * there too; none of that calls back here. Asking again on resume is the only way to be right
+     * after the user has been somewhere else to fix it.
+     */
+    fun refreshShizuku() {
+        val st = ShizukuAvailability.current(getApplication())
+        state = state.copy(
+            shizukuNotice = ShizukuAvailability.describe(st),
+            shizukuReady = st == ShizukuAvailability.State.READY,
+            shizukuHint = ShizukuAvailability.actionHint(st),
+            shizukuState = st,
+        )
+    }
+
     override fun onCleared() {
         stopShizukuObserver()
+        // A NetworkCallback outlives the object that registered it: the system holds the reference,
+        // so a ViewModel dying mid-run with listeners still up leaks one for the life of the
+        // process. viewModelScope is already cancelled by now, hence a detached scope purely to
+        // hang up — its results are discarded, only the unregistration matters.
+        val leftovers = activeCollectors
+        activeCollectors = emptyList()
+        if (leftovers.isNotEmpty()) {
+            kotlinx.coroutines.CoroutineScope(Dispatchers.IO).launch {
+                leftovers.forEach { runCatching { it.stop() } }
+            }
+        }
         super.onCleared()
     }
     // Results collected so far. A cancelled run must still be able to show what it measured.
@@ -90,6 +154,19 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
     private var runStartWall: String = ""
     private var runNetworks: List<app.echo_lot.measurement.Network> = emptyList()
     private var runShizukuOk = false
+    private var runConstraints = Constraints()
+    private var runMode: RunMode = RunMode.SHORT
+
+    /**
+     * The listeners of the run in flight.
+     *
+     * Held on the ViewModel rather than inside `measure()` because [cancel] has to be able to reach
+     * them: the run job is dead by then, and what the listeners gathered up to that moment is the
+     * most valuable part of a long run that was cut short. They own their own coroutine scopes for
+     * the same reason — cancelling the run must stop the sampling without discarding the samples.
+     */
+    private var activeCollectors: List<app.echo_lot.probe.Collector> = emptyList()
+    private var changeCollector: app.echo_lot.probe.NetworkChangeCollector? = null
 
     /** Two-clock ids: UUIDs + monotonic ns relative to a per-run origin. */
     private class RunIds : ProbeIds {
@@ -105,13 +182,17 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
      * from the user-facing upload so a debugging convenience can never be mistaken for, or
      * silently satisfy, the consent-gated one.
      */
-    fun run(devUpload: Boolean = false) {
+    fun run(mode: RunMode = RunMode.SHORT, devUpload: Boolean = false) {
         if (state.running) return
         collected.clear()
+        runConstraints = Constraints()
+        runMode = mode
+        val windowS = if (mode == RunMode.LONG) settings.longRunMinutes * 60 else 0
         state = state.copy(running = true, currentStep = "starting", document = null,
-            uploadStatus = null, archiveStatus = null)
+            uploadStatus = null, archiveStatus = null,
+            mode = mode, windowElapsedS = 0, windowTotalS = windowS)
         runJob = viewModelScope.launch {
-            val doc = withContext(Dispatchers.IO) { measure() }
+            val doc = withContext(Dispatchers.IO) { measure(mode) }
 
             step("archiving")
             val archived = withContext(Dispatchers.IO) { store.archive(doc) }
@@ -125,7 +206,13 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
             if (devUpload) {
                 state = state.copy(currentStep = "uploading report")
                 val r = withContext(Dispatchers.IO) { ReportUploader.upload(doc) }
-                status = if (r.ok) "uploaded ✓ ${r.detail}" else "upload failed: ${r.detail}"
+                status = when {
+                    r.ok -> "uploaded ✓ ${r.detail}"
+                    // Not a failure worth alarming about: the dev collection endpoint is simply
+                    // not configured, and the run is on the device either way.
+                    r.detail.startsWith("no upload URL") -> "run complete — read it with adb"
+                    else -> "upload failed: ${r.detail}"
+                }
             }
             if (archived != null && settings.autoUpload) {
                 state = state.copy(currentStep = "uploading to server")
@@ -136,6 +223,7 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
             state = UiState(
                 running = false, currentStep = null, document = doc,
                 uploadStatus = status, archiveStatus = archiveStatus,
+                mode = mode,
                 history = withContext(Dispatchers.IO) { store.list() },
             )
         }
@@ -215,11 +303,88 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
      *  history screen has been opened - the two disagreeing read as data loss. */
     fun archivedRunCount(): Int = store.list().size
 
+    private val account = Account(settings)
+
+    /** Name of whoever is signed in on this device, for the settings screen. */
+    var accountName by mutableStateOf(settings.accountName)
+        private set
+
+    /** Starts sign-in; the caller opens the returned URL in a browser. */
+    fun beginSignIn(open: (String) -> Unit) {
+        viewModelScope.launch {
+            state = state.copy(archiveStatus = "contacting the server …")
+            when (val r = withContext(Dispatchers.IO) { account.begin() }) {
+                is Account.SignInStart.Browser -> {
+                    state = state.copy(archiveStatus = "continue in your browser …")
+                    open(r.url)
+                }
+                is Account.SignInStart.Unavailable ->
+                    state = state.copy(archiveStatus = r.reason)
+            }
+        }
+    }
+
+    /** Completes sign-in from the echolot://auth redirect. */
+    fun completeSignIn(callbackUri: String) {
+        viewModelScope.launch {
+            val msg = withContext(Dispatchers.IO) { account.complete(callbackUri) }
+            accountName = settings.accountName
+            state = state.copy(archiveStatus = msg)
+        }
+    }
+
+    fun signOut() {
+        viewModelScope.launch {
+            val msg = withContext(Dispatchers.IO) { account.signOut() }
+            accountName = settings.accountName
+            state = state.copy(archiveStatus = msg)
+        }
+    }
+
     /** Redeems an enrollment link, from a paste or from an echolot:// deep link. */
     fun enroll(link: String, deviceName: String? = android.os.Build.MODEL) {
+        // Already enrolled? Ask first. The old credential is gone the moment this succeeds, and a
+        // link followed from a web page is one tap — far too little deliberation for that.
+        if (settings.serverConfigured) {
+            val target = app.echo_lot.protocol.EnrollmentLink.parse(link)?.controlUrl ?: link
+            state = state.copy(
+                pendingEnroll = PendingEnroll(
+                    link = link,
+                    // Compared against the link's URL, which names the server publicly — so this
+                    // has to be the public name too. Using the endpoint made re-enrolling with the
+                    // same server look like a move to a different one, because the endpoint and
+                    // the public name are deliberately different strings.
+                    currentServer = settings.serverPublicUrl,
+                    newServer = target,
+                )
+            )
+            return
+        }
+        doEnroll(link, deviceName)
+    }
+
+    /** The user confirmed replacing an existing enrollment. */
+    fun confirmEnroll(deviceName: String? = android.os.Build.MODEL) {
+        val pending = state.pendingEnroll ?: return
+        state = state.copy(pendingEnroll = null)
+        doEnroll(pending.link, deviceName)
+    }
+
+    fun cancelEnroll() {
+        state = state.copy(
+            pendingEnroll = null,
+            enrollStatus = "Kept the existing enrollment; nothing changed.",
+        )
+    }
+
+    private fun doEnroll(link: String, deviceName: String?) {
         viewModelScope.launch {
-            state = state.copy(archiveStatus = "enrolling …")
-            state = state.copy(archiveStatus = withContext(Dispatchers.IO) { store.enroll(link, deviceName) })
+            state = state.copy(enrollStatus = "Enrolling …")
+            val result = withContext(Dispatchers.IO) { store.enroll(link, deviceName) }
+            // A new server means a new canary zone; the old one would describe somebody else's
+            // deployment. Cleared rather than kept, and relearned from the next profile fetch.
+            settings.canaryZone = ""
+            state = state.copy(enrollStatus = result)
         }
     }
 
@@ -246,45 +411,209 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
     /**
      * Stops an in-flight run and shows what was measured so far. Deliberately does NOT upload:
      * a partial run is for the person looking at the screen, not for the record.
+     *
+     * Cancelling a long run must still hand back what the listeners heard — two minutes of watching
+     * is worth reporting, and throwing it away because the user did not wait for the third would be
+     * the worst possible answer to "I've seen enough". The harvest runs on [viewModelScope] rather
+     * than in the (now cancelled) run job, and the listeners' own scopes are what kept their data
+     * alive long enough to collect.
      */
     fun cancel() {
-        if (!state.running) return
+        if (!state.running || cancelling) return
+        cancelling = true
         runJob?.cancel()
+        state = state.copy(currentStep = "stopping listeners")
+        viewModelScope.launch {
+            withContext(Dispatchers.IO) { stopCollectors() }
             val doc = buildDocument(collected.toList())
+            cancelling = false
             state = UiState(
                 running = false, currentStep = null, document = doc,
                 uploadStatus = "cancelled after ${collected.size} test(s) — shown locally, not uploaded",
                 archiveStatus = "partial run — not archived",
+                mode = runMode,
                 history = state.history,
             )
         }
+    }
 
-    private suspend fun measure(): MeasurementDocument {
+    private var cancelling = false
+
+    /**
+     * Stops every listener, folds its Test into the run, and attaches the observed network changes
+     * to `networks[]`. Idempotent — the normal path and the cancel path both call it, and only the
+     * first does anything.
+     */
+    /**
+     * The discovery listeners the user selected for this run.
+     *
+     * Searches are paced across the window rather than fired at the start, so a device that was
+     * asleep for the first minute is still asked.
+     */
+    private fun discoveryCollectors(windowMs: Long): List<app.echo_lot.probe.Collector> {
+        val out = ArrayList<app.echo_lot.probe.Collector>(4)
+        if (settings.discoveryEnabled(DiscoveryIds.SSDP)) {
+            out.add(
+                app.echo_lot.probe.SsdpCollector(
+                    searchIntervalMs = (windowMs / 5).coerceAtLeast(30_000),
+                )
+            )
+        }
+        if (settings.discoveryEnabled(DiscoveryIds.WSD)) out.add(app.echo_lot.probe.WsdCollector())
+        if (settings.discoveryEnabled(DiscoveryIds.LLMNR)) out.add(app.echo_lot.probe.LlmnrCollector())
+        if (settings.discoveryEnabled(DiscoveryIds.NETBIOS)) out.add(app.echo_lot.probe.NetbiosCollector())
+        return out
+    }
+
+    /**
+     * A test recording that a listener was switched off, so its absence is never mistaken for its
+     * silence.
+     *
+     * The same reasoning as `run.mode`: a document in which `local.ssdp_inventory` is simply
+     * missing cannot tell a reader whether nothing announced itself or nobody was listening, and
+     * those are opposite conclusions about a network. SKIPPED with a reason is how the canary and
+     * STUN probes already say "not asked", so it is the shape a consumer already understands.
+     */
+    private fun notSelected(type: String, ids: ProbeIds): Test {
+        val at = ids.monoNs()
+        return Test(
+            id = ids.uuid(), type = type, tier = Tier.APP,
+            startedMonoNs = at, endedMonoNs = at,
+            status = TestStatus.SKIPPED,
+            evidence = kotlinx.serialization.json.JsonObject(
+                mapOf(
+                    "reason" to kotlinx.serialization.json.JsonPrimitive(
+                        "listener not selected for this run"
+                    )
+                )
+            ),
+        )
+    }
+
+    /** Registry ids for the selectable listeners, so the skipped-test record uses the real type. */
+    private fun discoveryType(id: String): String = when (id) {
+        DiscoveryIds.SSDP -> TestType.LOCAL_SSDP_INVENTORY
+        DiscoveryIds.WSD -> TestType.LOCAL_WSD_INVENTORY
+        DiscoveryIds.LLMNR -> TestType.LOCAL_LLMNR_INVENTORY
+        else -> TestType.LOCAL_NETBIOS_INVENTORY
+    }
+
+    private suspend fun stopCollectors(): List<Test> {
+        val running = activeCollectors
+        activeCollectors = emptyList()
+        val out = ArrayList<Test>()
+        for (c in running) {
+            val t = runCatching { c.stop() }.getOrNull() ?: continue
+            out.add(t)
+            collected.add(t)
+        }
+        changeCollector?.let { watcher ->
+            changeCollector = null
+            val byNetwork = runCatching { watcher.changesByNetwork() }.getOrDefault(emptyMap())
+            if (byNetwork.isNotEmpty()) {
+                runNetworks = runNetworks.map { n -> n.copy(changes = byNetwork[n.id] ?: n.changes) }
+            }
+        }
+        return out
+    }
+
+    private suspend fun measure(mode: RunMode): MeasurementDocument = coroutineScope {
         val ctx = getApplication<Application>()
         val ids = RunIds().also { runIds = it }
         val startWall = Instant.now().toString().also { runStartWall = it }
+        val windowMs = if (mode == RunMode.LONG) settings.longRunMinutes * 60_000L else 0L
 
         step("reading networks")
         val entries = NetworkInventory.snapshot(ctx)
         val networks = entries.map { it.model }.also { runNetworks = it }
 
-        val probes: List<Probe> = listOf(
+        // What will this run be prevented from measuring? Decided up front, from one throwaway
+        // bind per network, so the document can say so instead of leaving it to be inferred from
+        // per-test `attempted: false` breadcrumbs (measurement-schema.md §3 `constraints`).
+        runConstraints = app.echo_lot.probe.ConstraintDetector.detect(ctx, entries)
+
+        // Listeners first, at t=0, so the battery itself runs *inside* the observed window: a link
+        // that drops while the DNS probe is timing out is then recorded as a drop rather than
+        // guessed at from a failure.
+        var ticker: kotlinx.coroutines.Job? = null
+        if (mode == RunMode.LONG) {
+            step("starting listeners")
+            val watcher = app.echo_lot.probe.NetworkChangeCollector(entries).also { changeCollector = it }
+            val collectors = listOf<app.echo_lot.probe.Collector>(
+                watcher,
+                app.echo_lot.probe.WifiSignalCollector(entries),
+                app.echo_lot.probe.PingSeriesCollector(),
+                // mDNS is a listener wearing a probe's clothes, so in long mode it listens for the
+                // window instead of blocking the battery for it. Two seconds short of the window,
+                // so it finishes just before everything is stopped rather than just after.
+                app.echo_lot.probe.ProbeCollector(
+                    app.echo_lot.probe.MdnsInventoryProbe(
+                        listenMs = (windowMs - 2_000).coerceAtLeast(10_000)
+                    )
+                ),
+                // The rest of what a segment says about itself unprompted. All passive listeners,
+                // which is exactly why they belong to long mode: the announcements are periodic
+                // and sparse, so a thirty-second run mostly hears silence and would report an
+                // empty network as confidently as a quiet one.
+                //
+                // Searches are paced across the window rather than fired at the start: a device
+                // that was asleep for the first minute still gets asked. NetBIOS is included
+                // knowing it will usually report `unsupported` — UDP 137 is privileged, so the
+                // app tier cannot bind it — because a recorded reason beats an absent test, and
+                // the decoder is ready for the Shizuku tier.
+            ) + discoveryCollectors(windowMs)
+            activeCollectors = collectors
+            for (c in collectors) runCatching { c.start(ctx, ids) }
+            // One ticker for the whole run: the battery does not report progress by the second, and
+            // without this the elapsed/remaining line would freeze for as long as the slowest probe.
+            ticker = launch {
+                while (isActive) {
+                    val elapsedS = (ids.monoNs() / 1_000_000_000L).toInt()
+                    state = state.copy(
+                        windowElapsedS = elapsedS.coerceAtMost((windowMs / 1000).toInt()),
+                        windowTotalS = (windowMs / 1000).toInt(),
+                    )
+                    kotlinx.coroutines.delay(1000)
+                }
+            }
+        }
+
+        val probes: List<Probe> = listOfNotNull(
             LinkSnapshotProbe(entries),
             RouterIdentityProbe(entries),
             IcmpProbe(entries, v6 = false),
             IcmpProbe(entries, v6 = true),
+            // Folded from the prober after hardware validation: errqueue traceroute (no root,
+            // no JNI) and the mDNS service inventory / VLAN-leakage detector.
+            app.echo_lot.probe.TracerouteProbe(),
+            // Absent from a long run's battery: it runs there as a collector for the whole window
+            // instead, and running it in both places would query the same services twice.
+            if (mode == RunMode.LONG) null else app.echo_lot.probe.MdnsInventoryProbe(),
             CaptivePortalProbe(entries),
             // Canary zone served by the Echolot probe server (probe-protocol §6.1). Hardcoded to
             // the reference deployment until profiles/enrollment land in the UI.
-            DnsCanaryProbe(canaryZone = "c.echo-lot.app", sessionPrefix = "adhoc"),
-            StunProbe(serverHost = "fmr-1.echo-lot.app"),
+            // Both target whatever server this device is enrolled with, not the deployment the
+            // app happened to be developed against. With no server configured they get blank
+            // strings and report themselves skipped, which is the honest outcome — the
+            // alternative measures someone else's infrastructure and calls it your network.
+            // Before the canary: "can this device resolve at all" has to be answered before
+            // "are the answers being tampered with" means anything.
+            app.echo_lot.probe.DnsResolverProbe(entries),
+            DnsCanaryProbe(canaryZone = settings.canaryZone, sessionPrefix = "adhoc"),
+            StunProbe(serverHost = settings.serverHost()),
+            // Corroboration for icmp.ping6's silence: a real TCP connection over IPv6. Only its
+            // failure, on a network that advertises IPv6, justifies calling IPv6 broken.
+            app.echo_lot.probe.V6ConnectProbe(entries, serverHost = settings.serverHost()),
         )
 
         // Plan the run first: the Shizuku battery is counted alongside the app-tier probes so
-        // the bar reflects the whole run. Estimates are per-probe (see Probe.estimatedMs).
-        val shizukuEstimateMs = 8_000L
+        // the bar reflects the whole run. Estimates prefer what THIS device measured on recent
+        // runs (Settings EMA); Probe.estimatedMs is only the cold-start seed — a fixed table
+        // cannot know whether ICMPv6 answers in milliseconds here or waits out its timeout.
+        fun estimateOf(p: Probe) = settings.learnedDurationMs(p.type) ?: p.estimatedMs
+        val shizukuEstimateMs = settings.learnedDurationMs(SHIZUKU_DURATION_KEY) ?: 8_000L
         val totalSteps = probes.size + 1
-        var remainingMs = probes.sumOf { it.estimatedMs } + shizukuEstimateMs
+        var remainingMs = probes.sumOf { estimateOf(it) } + shizukuEstimateMs
         state = state.copy(stepsDone = 0, stepsTotal = totalSteps,
             etaSeconds = ((remainingMs + 999) / 1000).toInt())
 
@@ -304,24 +633,52 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
                 }
             )
             tests.add(result); collected.add(result)
-            remainingMs -= p.estimatedMs
+            settings.recordDurationMs(p.type, (result.endedMonoNs - result.startedMonoNs) / 1_000_000)
+            remainingMs -= estimateOf(p)
         }
 
-        // Shizuku shell tier — self-degrades to UNSUPPORTED when Shizuku isn't running.
+        // Shizuku shell tier — self-degrades to UNSUPPORTED when Shizuku isn't running. One
+        // battery, three tests: the raw captures plus the parsed ra_source/arp_watch views.
         step("link.ip_monitor (shizuku)", done = probes.size, total = totalSteps, etaMs = shizukuEstimateMs)
-        val shizukuTest = try {
+        val shizukuT0 = System.nanoTime()
+        val shizukuTests = try {
             ShizukuProbe().run(ctx, ids::uuid, ids::monoNs)
         } catch (t: Throwable) {
-            Test(
+            listOf(Test(
                 id = ids.uuid(), type = TestType.LINK_IP_MONITOR, tier = Tier.SHIZUKU,
                 startedMonoNs = ids.monoNs(), endedMonoNs = ids.monoNs(),
                 status = TestStatus.FAILED, error = TestError("uncaught", t.message ?: t.javaClass.simpleName),
-            )
+            ))
+        }
+        // One key for the whole step: the three tests come out of one shell battery, and the
+        // bar plans them as one step.
+        settings.recordDurationMs(SHIZUKU_DURATION_KEY, (System.nanoTime() - shizukuT0) / 1_000_000)
+        tests.addAll(shizukuTests); collected.addAll(shizukuTests)
+        // "Shizuku tier ran" is the battery's verdict — the derived tests can be PARTIAL on a
+        // perfectly healthy shell tier (e.g. an RA-less v4-only link).
+        runShizukuOk = shizukuTests.any {
+            it.type == TestType.LINK_IP_MONITOR &&
+                (it.status == TestStatus.OK || it.status == TestStatus.PARTIAL)
         }
-        tests.add(shizukuTest); collected.add(shizukuTest)
-        runShizukuOk = shizukuTest.status == TestStatus.OK || shizukuTest.status == TestStatus.PARTIAL
 
-        return buildDocument(tests)
+        if (mode == RunMode.LONG) {
+            // The battery finishing is not the run finishing. Everything the long mode exists for
+            // happens in the minutes after this point, so the run waits the window out — in one
+            // second steps, because `delay` is what makes a five-minute wait cancellable.
+            while (true) {
+                val elapsedMs = ids.monoNs() / 1_000_000
+                val remainingS = ((windowMs - elapsedMs + 999) / 1000).toInt()
+                if (remainingS <= 0) break
+                step("listening · ${remainingS}s left", done = totalSteps, total = totalSteps, etaMs = windowMs - elapsedMs)
+                kotlinx.coroutines.delay(minOf(1000L, windowMs - elapsedMs))
+            }
+            step("collecting listeners")
+            tests.addAll(stopCollectors())
+        }
+        // Before the enclosing coroutineScope waits for its children, or the run would never end.
+        ticker?.cancel()
+
+        buildDocument(tests)
     }
 
     /** Assembles a document from whatever tests are in hand — used for both full and cancelled runs. */
@@ -329,7 +686,7 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
         val findings = deriveFindings(tests, runNetworks)
         return MeasurementDocument(
             run = Run(
-                id = runIds.uuid(), trigger = Trigger.MANUAL, startedAt = runStartWall,
+                id = runIds.uuid(), trigger = Trigger.MANUAL, mode = runMode, startedAt = runStartWall,
                 endedAt = Instant.now().toString(),
                 clock = Clock(monoOriginWall = runStartWall),
                 app = AppInfo(
@@ -340,31 +697,221 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
                     androidSdk = Build.VERSION.SDK_INT, androidRelease = Build.VERSION.RELEASE,
                 ),
                 tiers = Tiers(app = true, shizuku = runShizukuOk),
+                constraints = runConstraints,
             ),
             networks = runNetworks,
             tests = tests,
             findings = findings,
-            summary = Verdicts.derive(tests, findings),
+            summary = Verdicts.derive(tests, findings, runConstraints),
         )
     }
 
     /**
-     * Was IPv6 actually provisioned on any network? A global (non-link-local) v6 address or a
-     * v6 default route means the network claims to offer IPv6 — link-local only does not count.
+     * Was IPv6 provisioned on the network a test actually ran over?
+     *
+     * This deliberately asks about one network rather than about the device. Answering "does any
+     * network here have IPv6" produces a real false positive on a phone, and it is not hypothetical:
+     * an IPv4-only wifi with working cellular alongside it reports "IPv6 is configured, but ICMPv6
+     * gets no reply" — configured on cellular, pinged over wifi, and the two never met.
+     *
+     * A global (non-link-local) address or a v6 default route means the network claims to offer
+     * IPv6; link-local only does not count, since every interface has one.
      */
-    private fun ipv6Provisioned(networks: List<app.echo_lot.measurement.Network>): Boolean =
-        networks.any { n ->
+    private fun ipv6Provisioned(
+        networks: List<app.echo_lot.measurement.Network>,
+        networkRef: String?,
+    ): Boolean {
+        // No reference means the test was not per-network; fall back to the device-wide reading
+        // rather than silently reporting nothing.
+        val scope = networks.filter { networkRef == null || it.id == networkRef }
+        return scope.any { n ->
             n.link.addresses.any { a ->
                 a.addr.contains(':') &&
                     !a.addr.startsWith("fe80", ignoreCase = true) &&
                     !a.addr.startsWith("::1")
             } || n.link.routes.any { it.dst == "::/0" }
         }
+    }
+
+    /**
+     * Per-network ICMP outcomes, keyed by network id.
+     *
+     * Reads the structured evidence the probe records rather than its prose detail — a finding
+     * that depended on the wording of a human-readable string would break silently the first time
+     * that wording improved.
+     */
+    /** What one network's ICMP attempt did: whether it ran at all, and whether it was answered. */
+    private data class IcmpOutcome(val attempted: Boolean, val ok: Boolean)
+
+    /**
+     * Per-network ICMP outcomes, keyed by network id.
+     *
+     * Reads the structured evidence the probe records rather than its prose detail — a finding
+     * that depended on the wording of a human-readable string would break silently the first time
+     * that wording improved.
+     */
+    private fun icmpResults(t: Test): Map<String, IcmpOutcome> {
+        val out = HashMap<String, IcmpOutcome>()
+        val ev = t.evidence ?: return out
+        for ((_, v) in ev) {
+            val o = v as? kotlinx.serialization.json.JsonObject ?: continue
+            val ref = (o["network_ref"] as? kotlinx.serialization.json.JsonPrimitive)?.content ?: continue
+            fun flag(k: String) = (o[k] as? kotlinx.serialization.json.JsonPrimitive)?.content == "true"
+            out[ref] = IcmpOutcome(attempted = flag("attempted"), ok = flag("ok"))
+        }
+        return out
+    }
+
+    /** Human-facing name for the network a test ran over; falls back to something readable. */
+    private fun ifaceOf(networks: List<app.echo_lot.measurement.Network>, ref: String?): String =
+        networks.firstOrNull { it.id == ref }?.iface?.takeIf { it.isNotBlank() } ?: "this network"
 
     /** Minimal first-pass findings from device-tier evidence; the registry grows with the suite. */
     private fun deriveFindings(tests: List<Test>, networks: List<app.echo_lot.measurement.Network>): List<Finding> {
         val out = ArrayList<Finding>()
         val ids = RunIds()
+        val linkEvidence = tests.filter { it.type == TestType.LINK_SNAPSHOT }.map { EvidenceRef(it.id) }
+
+        // Said as a finding, not only as run.constraints: the constraints block is for machines
+        // aggregating thousands of runs, this is for the person reading this one. Both must exist —
+        // a constrained run with a quiet findings list still reads as "nothing wrong here".
+        if (runConstraints.constrained) {
+            val blocked = runConstraints.unmeasuredNetworks
+                .joinToString(", ") { id -> ifaceOf(networks, id) }
+                .ifBlank { "the underlying networks" }
+            // Three distinct situations share this finding code, and naming the wrong one costs
+            // trust: claiming "a VPN is active" right after the user disconnected theirs is how
+            // this text was first proven wrong on hardware.
+            val (title, description) = when {
+                runConstraints.vpnActive && runConstraints.perNetworkBlocked ->
+                    "A VPN is active — $blocked could not be measured" to
+                        ("Android refuses to let apps send on the networks beneath an active " +
+                            "VPN (that is how it prevents traffic leaking around the tunnel), " +
+                            "so every per-network test here measured the tunnel or nothing. " +
+                            "Nothing in this run says anything about $blocked. To measure them, " +
+                            "disconnect the VPN and run again.")
+                runConstraints.perNetworkBlocked ->
+                    "The OS refused sends on $blocked" to
+                        ("Android denied this app permission to send on $blocked (EPERM on " +
+                            "bind), so nothing in this run says anything about it. The usual " +
+                            "cause is a VPN — Android walls off the networks beneath a tunnel — " +
+                            "but the refusal can also outlast one, and some networks are " +
+                            "reserved for the system entirely. If no VPN is connected, this is " +
+                            "a restriction on the app rather than a fault in the network.")
+                else ->
+                    "A VPN holds the default route" to
+                        ("Everything using the default route in this run describes the tunnel, " +
+                            "not the network it rides on. Per-network measurements were " +
+                            "permitted and did measure the underlying networks.")
+            }
+            out.add(
+                Finding(
+                    id = ids.uuid(),
+                    code = FindingRegistry.MEASUREMENT_VPN_CONSTRAINED.code,
+                    category = FindingRegistry.MEASUREMENT_VPN_CONSTRAINED.category,
+                    severity = FindingRegistry.MEASUREMENT_VPN_CONSTRAINED.severity,
+                    confidence = Confidence.HIGH,
+                    title = title,
+                    description = description,
+                    evidenceRefs = linkEvidence,
+                )
+            )
+        }
+        // The one finding only a long run can reach. Derived from networks[].changes[] rather than
+        // from the watcher's evidence, because the changes are the schema's own record of what
+        // happened (§4) and re-parsing the test would be a second, divergent reading of it. A short
+        // run has an empty changes[] and therefore never gets here — which is correct, not a gap:
+        // it did not watch, so it has nothing to say either way.
+        val watchTest = tests.firstOrNull {
+            it.type == TestType.LINK_IP_MONITOR && it.tier == Tier.APP
+        }
+        if (watchTest != null) {
+            for (n in networks) {
+                val cycles = NetworkChanges.flapCyclesOf(n.changes)
+                if (cycles < 1) continue
+                val where = n.iface?.takeIf { it.isNotBlank() } ?: "this network"
+                out.add(
+                    Finding(
+                        id = ids.uuid(),
+                        code = FindingRegistry.LINK_FLAPPING.code,
+                        category = FindingRegistry.LINK_FLAPPING.category,
+                        // Escalated on repetition: once is a hiccup worth knowing about, three
+                        // times in one window is the reason someone's calls keep dropping.
+                        severity = if (cycles >= 3) Severity.HIGH else FindingRegistry.LINK_FLAPPING.severity,
+                        confidence = Confidence.HIGH,
+                        title = if (cycles == 1) "$where dropped and came back during the run"
+                        else "$where dropped and came back $cycles times during the run",
+                        description = "A listener watched this link for the whole measurement and " +
+                            "saw it go away and return " +
+                            (if (cycles == 1) "once" else "$cycles times") + ". Every one-shot " +
+                            "test in this run may still have passed — the probes on either side of " +
+                            "a gap succeed — so this is the kind of fault a quick measurement " +
+                            "cannot find. Connections in flight are dropped each time it happens: " +
+                            "calls end, downloads stall, and anything long-lived reconnects. On " +
+                            "wifi the usual causes are a weak or contended channel, band steering, " +
+                            "or an access point restarting; on cellular, handovers at the edge of " +
+                            "coverage. The timeline of every change is in networks[].changes[].",
+                        evidenceRefs = listOf(EvidenceRef(watchTest.id)),
+                    )
+                )
+            }
+        }
+
+        val shapes = V6Analysis.classify(networks)
+        // Named per interface: on a phone several networks are up at once, and "IPv6 is broken" is
+        // useless when wifi is the broken one and cellular is fine.
+        for (sh in shapes.filter { it.addressWithoutRoute }) {
+            val where = if (sh.iface.isBlank()) "This device" else sh.iface
+            out.add(
+                Finding(
+                    id = ids.uuid(),
+                    code = FindingRegistry.V6_NO_DEFAULT_ROUTE.code,
+                    category = FindingRegistry.V6_NO_DEFAULT_ROUTE.category,
+                    severity = if (sh.tunnel) Severity.INFO else Severity.MEDIUM,
+                    confidence = Confidence.HIGH,
+                    title = if (sh.tunnel) {
+                        "IPv6 reaches only the destinations a tunnel routes ($where)"
+                    } else {
+                        "IPv6 address with no default route ($where)"
+                    },
+                    description = "$where has a global IPv6 address but no IPv6 default route, so " +
+                        "IPv6 reaches only destinations covered by a specific route. " +
+                        if (sh.tunnel) {
+                            "A tunnel interface holds those routes, so this looks deliberate. " +
+                                "Worth knowing rather than fixing: applications holding a global " +
+                                "address will still try IPv6 first and stall for anything outside " +
+                                "the tunnel's routes."
+                        } else {
+                            "Nothing is routing the rest, so the network handed out an address it " +
+                                "does not carry traffic for — applications will try IPv6 first " +
+                                "and wait for it to fail."
+                        },
+                    evidenceRefs = linkEvidence,
+                )
+            )
+        }
+        for (sh in shapes.filter { it.routeWithoutAddress }) {
+            val where = if (sh.iface.isBlank()) "This network" else sh.iface
+            out.add(
+                Finding(
+                    id = ids.uuid(),
+                    code = FindingRegistry.V6_ROUTE_WITHOUT_ADDRESS.code,
+                    category = FindingRegistry.V6_ROUTE_WITHOUT_ADDRESS.category,
+                    severity = Severity.MEDIUM,
+                    confidence = Confidence.HIGH,
+                    title = "IPv6 router advertised, but no address was configured ($where)",
+                    description = "$where has an IPv6 default route but no global IPv6 address. " +
+                        "The router is advertising itself as an IPv6 gateway while SLAAC produced " +
+                        "no usable address — a missing prefix option, a prefix without the " +
+                        "autonomous flag, or DHCPv6-only addressing that did not complete. Hosts " +
+                        "believe IPv6 is available and pay a connection timeout on every " +
+                        "dual-stack destination before falling back to IPv4, which is felt as " +
+                        "general slowness with no packet loss to explain it.",
+                    evidenceRefs = linkEvidence,
+                )
+            )
+        }
+
         for (t in tests) {
             if (t.type == TestType.NET_CAPTIVE_PORTAL) {
                 val ev = t.evidence?.toString() ?: ""
@@ -432,31 +979,185 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
                     )
                 }
             }
-            if (t.type == TestType.ICMP_PING6 && t.status == TestStatus.FAILED) {
-                // A network with no IPv6 at all is NORMAL — most networks are still IPv4-only,
-                // and that is not a defect. What IS a defect is IPv6 that the network claims to
-                // provide (a global address or a default route from RA/DHCPv6) but that does not
-                // work: that causes Happy-Eyeballs delays, timeouts and hangs. So the severity
-                // depends on whether v6 was provisioned at all.
-                if (ipv6Provisioned(networks)) {
+            if (t.type == TestType.DNS_RESOLVER && t.status == TestStatus.OK) {
+                // One finding per network: on a phone the wifi resolver can be wedged while
+                // cellular is fine, and "DNS is broken" would be wrong about half the device.
+                val ev = t.evidence
+                if (ev != null) {
+                    for ((_, v) in ev) {
+                        val o = v as? kotlinx.serialization.json.JsonObject ?: continue
+                        fun str(k: String) =
+                            (o[k] as? kotlinx.serialization.json.JsonPrimitive)?.content
+                        val verdict = str("verdict")
+                        val ref0 = str("network_ref")
+                        val iface0 = networks.firstOrNull { it.id == ref0 }?.iface
+                            ?.takeIf { it.isNotBlank() } ?: "this network"
+                        if (verdict == "search domain swallows queries") {
+                            // Severity follows the harm, not the shape: the same misconfiguration
+                            // is fatal on a resolver that tries the search form and invisible on
+                            // one that does not, and saying "high" for a network that currently
+                            // resolves fine would be crying wolf.
+                            val breaking = str("system_resolves") != "true"
                             out.add(
                                 Finding(
-                            id = ids.uuid(), code = FindingRegistry.V6_BROKEN.code,
-                            category = FindingRegistry.V6_BROKEN.category,
-                            severity = FindingRegistry.V6_BROKEN.severity, confidence = Confidence.HIGH,
-                            title = "IPv6 is configured but not working",
-                            description = "This network advertises IPv6 (a global address and/or a default route), but ICMPv6 got no reply on any network. Half-configured IPv6 is worse than none: connections try IPv6 first and stall before falling back.",
+                                    id = ids.uuid(),
+                                    code = FindingRegistry.DNS_SEARCH_DOMAIN_UNANSWERED.code,
+                                    category = FindingRegistry.DNS_SEARCH_DOMAIN_UNANSWERED.category,
+                                    severity = if (breaking) Severity.HIGH else Severity.MEDIUM,
+                                    confidence = Confidence.HIGH,
+                                    title = "The network's search domain swallows DNS queries ($iface0)",
+                                    description = "This network hands out " +
+                                        "${str("search_domains") ?: "a search domain"} as a DNS " +
+                                        "search domain, but its server never answers queries under " +
+                                        "it — not even to say the name does not exist. Resolvers " +
+                                        "append that domain to lookups, so they wait for a reply " +
+                                        "that never comes. " +
+                                        (if (breaking) {
+                                            "That is why names are not resolving on this device."
+                                        } else {
+                                            "Name resolution still works here, because this " +
+                                                "resolver tries the plain name first — another " +
+                                                "device on the same network may fail outright."
+                                        }) +
+                                        " Fix it on the router: either stop advertising the search " +
+                                        "domain, or make the server answer for it, including " +
+                                        "NXDOMAIN for names it does not have. Note that .local is " +
+                                        "reserved for mDNS (RFC 6762) and is widely dropped by " +
+                                        "design; home.arpa (RFC 8375) is the name reserved for this.",
                                     evidenceRefs = listOf(EvidenceRef(t.id)),
                                 )
                             )
-                } else {
+                            continue
+                        }
+                        if (verdict != "server answers, device resolver does not") continue
+                        val ref = str("network_ref")
+                        val where = networks.firstOrNull { it.id == ref }?.iface
+                            ?.takeIf { it.isNotBlank() } ?: "this network"
+                        out.add(
+                            Finding(
+                                id = ids.uuid(),
+                                code = FindingRegistry.DNS_SYSTEM_RESOLVER_BROKEN.code,
+                                category = FindingRegistry.DNS_SYSTEM_RESOLVER_BROKEN.category,
+                                severity = FindingRegistry.DNS_SYSTEM_RESOLVER_BROKEN.severity,
+                                confidence = Confidence.HIGH,
+                                title = "This device cannot resolve names, but the DNS server is fine ($where)",
+                                description = "A DNS query sent straight from this device was " +
+                                    "answered by ${str("servers") ?: "the configured server"} with " +
+                                    "a valid result, yet asking Android to resolve the same name " +
+                                    "fails. Whatever is wrong sits between this device's resolver " +
+                                    "and a server that demonstrably works. " +
+                                    "Turning wifi off and on, or rejoining the network, clears the " +
+                                    "common case. If it survives a restart it is not a stuck " +
+                                    "resolver: look for something on this device that filters DNS " +
+                                    "— an ad blocker, a private-DNS or VPN app — or a per-device " +
+                                    "rule on the router aimed at this client.",
+                                evidenceRefs = listOf(EvidenceRef(t.id)),
+                            )
+                        )
+                    }
+                }
+            }
+            if (t.type == TestType.ICMP_PING6) {
+                // A network with no IPv6 at all is NORMAL — most networks are still IPv4-only, and
+                // that is not a defect. What IS a defect is IPv6 the network claims to provide (a
+                // global address or a default route from RA/DHCPv6) that does not work: that causes
+                // Happy-Eyeballs delays, timeouts and hangs.
+                //
+                // Judged per network, from the per-network evidence rather than the aggregate
+                // status. The aggregate can only say "some network answered", and on a phone with
+                // wifi and cellular up at once that is how "IPv6 is configured but gets no reply"
+                // ends up describing a network where IPv6 was never configured in the first place.
+                val results = icmpResults(t)
+                // The corroborating witness: did a real TCP connection over IPv6 work on this
+                // network? Same evidence shape as the ICMP probe, so the same parser reads it.
+                val v6ConnTest = tests.firstOrNull { it.type == TestType.V6_BROKENNESS }
+                val v6Conn = v6ConnTest?.let { icmpResults(it) } ?: emptyMap()
+                var anyV6Network = false
+                for (n in networks) {
+                    val provisioned = ipv6Provisioned(networks, n.id)
+                    if (provisioned) anyV6Network = true
+                    val r = results[n.id] ?: continue
+                    // Silence is only evidence if something was actually sent. A bind that failed
+                    // with EPERM says the app could not use the interface, which is a fact about
+                    // this app's permissions and says nothing whatsoever about the network.
+                    if (!provisioned || !r.attempted || r.ok) continue
+                    val where = n.iface?.takeIf { it.isNotBlank() } ?: "this network"
+                    val conn = v6Conn[n.id]
+                    val evidence = listOfNotNull(
+                        EvidenceRef(t.id), v6ConnTest?.let { EvidenceRef(it.id) },
+                    )
+                    when {
+                        // TCP over IPv6 worked: the silence is filtering, and can be said so.
+                        conn?.ok == true -> out.add(
+                            Finding(
+                                id = ids.uuid(), code = FindingRegistry.V6_NO_ICMP_REPLY.code,
+                                category = FindingRegistry.V6_NO_ICMP_REPLY.category,
+                                severity = FindingRegistry.V6_NO_ICMP_REPLY.severity,
+                                confidence = Confidence.HIGH,
+                                title = "ICMPv6 is filtered here — IPv6 itself works ($where)",
+                                description = "$where answered a real TCP connection over IPv6, " +
+                                    "so IPv6 works — but ICMPv6 echo got no reply, so something " +
+                                    "on this network filters ICMPv6. That is a fault in its own " +
+                                    "right even though connections succeed: Path MTU Discovery " +
+                                    "depends on ICMPv6, so large packets can vanish rather than " +
+                                    "being reported as too big.",
+                                evidenceRefs = evidence,
+                            )
+                        )
+                        // Both transports failed on a network that advertises IPv6: broken, and
+                        // now with the evidence the original v6.broken never had.
+                        conn != null && conn.attempted -> out.add(
+                            Finding(
+                                id = ids.uuid(), code = FindingRegistry.V6_BROKEN.code,
+                                category = FindingRegistry.V6_BROKEN.category,
+                                severity = FindingRegistry.V6_BROKEN.severity,
+                                confidence = Confidence.HIGH,
+                                title = "IPv6 is advertised but does not work ($where)",
+                                description = "$where advertises IPv6 (a global address and/or a " +
+                                    "default route), but neither ICMPv6 echo nor a TCP connection " +
+                                    "over IPv6 got through — two independent transports, both " +
+                                    "silent. Applications will try IPv6 first and wait out a " +
+                                    "timeout on every dual-stack destination before falling back " +
+                                    "to IPv4, felt as everything being slow with no loss to " +
+                                    "explain it. The network is announcing a service it does not " +
+                                    "deliver; the fix belongs on the router or upstream.",
+                                evidenceRefs = evidence,
+                            )
+                        )
+                        // No corroboration available (no server configured, or the connect never
+                        // got as far as sending): the honest two-explanation reading stands.
+                        else -> out.add(
+                            Finding(
+                                id = ids.uuid(), code = FindingRegistry.V6_NO_ICMP_REPLY.code,
+                                category = FindingRegistry.V6_NO_ICMP_REPLY.category,
+                                severity = FindingRegistry.V6_NO_ICMP_REPLY.severity,
+                                confidence = Confidence.MEDIUM,
+                                title = "IPv6 is configured, but ICMPv6 gets no reply ($where)",
+                                description = "$where advertises IPv6 (a global address and/or a " +
+                                    "default route), but ICMPv6 echo got no reply over it. That has " +
+                                    "two explanations which look identical from here: IPv6 is broken, " +
+                                    "or ICMPv6 is filtered while IPv6 itself works. Filtering is " +
+                                    "common and is a fault in its own right — it breaks Path MTU " +
+                                    "Discovery, so large packets vanish rather than being reported as " +
+                                    "too big.",
+                                evidenceRefs = listOf(EvidenceRef(t.id)),
+                            )
+                        )
+                    }
+                }
+                if (!anyV6Network) {
+                    // Said once for the device, not once per interface: "this network is IPv4-only"
+                    // repeated per interface reads as several problems instead of one observation.
                     out.add(
                         Finding(
                             id = ids.uuid(), code = FindingRegistry.V6_NOT_OFFERED.code,
                             category = FindingRegistry.V6_NOT_OFFERED.category,
-                            severity = FindingRegistry.V6_NOT_OFFERED.severity, confidence = Confidence.HIGH,
+                            severity = FindingRegistry.V6_NOT_OFFERED.severity,
+                            confidence = Confidence.HIGH,
                             title = "IPv4-only network (no IPv6 offered)",
-                            description = "No IPv6 address or default route was provisioned, so IPv6 tests could not run. This is normal — many networks are still IPv4-only and it is not a fault.",
+                            description = "No IPv6 address or default route was provisioned on " +
+                                "any active network, so IPv6 tests could not run. This is normal " +
+                                "— many networks are still IPv4-only and it is not a fault.",
                             evidenceRefs = listOf(EvidenceRef(t.id)),
                         )
                     )
@@ -472,4 +1173,9 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
             etaSeconds = if (etaMs >= 0) ((etaMs + 999) / 1000).toInt() else state.etaSeconds,
         )
     }
+
+    private companion object {
+        /** Duration-learning key for the Shizuku step, which is three tests but one battery. */
+        const val SHIZUKU_DURATION_KEY = "shizuku.battery"
+    }
 }

echolot-app/app/src/main/kotlin/app/echo_lot/app/Settings.kt

@@ -24,6 +24,7 @@ class Settings(context: Context) {
     private val prefs: SharedPreferences =
         context.getSharedPreferences("echolot-settings", Context.MODE_PRIVATE)
 
+
     // ---- archive ---------------------------------------------------------------------
 
     var archiveEnabled: Boolean
@@ -50,6 +51,87 @@ class Settings(context: Context) {
         maxTotalBytes = maxTotalMb.toLong() * 1024 * 1024,
     )
 
+    // ---- measurement -------------------------------------------------------------------
+
+    /**
+     * How long a long run listens, in minutes. Offered as 1 / 5 / 15.
+     *
+     * 5 is the default because it is the shortest window in which the things long mode exists to
+     * catch — a link that flaps, a signal that decays as someone walks around, loss that comes in
+     * bursts — have a fair chance of happening at least twice. One minute is for checking that the
+     * mode works at all; fifteen is for chasing something already suspected.
+     *
+     * Clamped rather than trusted: a zero-minute long run would produce a document claiming a
+     * window it never watched, which is the one thing `run.mode` exists to prevent.
+     */
+    var longRunMinutes: Int
+        get() = prefs.getInt(LONG_RUN_MINUTES, 5).coerceIn(1, 60)
+        set(v) = prefs.edit().putInt(LONG_RUN_MINUTES, v.coerceIn(1, 60)).apply()
+
+    // ---- dev relay -----------------------------------------------------------------------
+
+    /**
+     * Whether this device relays adbd's wireless-debug endpoint to the enrolled server.
+     *
+     * Off by default and never implied by anything else: it publishes where this device can be
+     * reached for debugging, which is a decision rather than a side effect. Intended for a spare
+     * device parked on a test network — see AdbRelay for why the OnePlus is a poor host for it.
+     */
+    var adbRelayEnabled: Boolean
+        get() = prefs.getBoolean(ADB_RELAY, false)
+        set(v) = prefs.edit().putBoolean(ADB_RELAY, v).apply()
+
+    // ---- discovery listeners -------------------------------------------------------------
+
+    /**
+     * Which passive discovery listeners a long run starts.
+     *
+     * Selectable rather than fixed because they differ from the rest of the battery in kind: they
+     * record what OTHER devices on the segment broadcast about themselves — hostnames, models,
+     * printer names — and that is someone's choice to make per run, not a default to inherit.
+     * They also cost nothing to leave off, since a listener that never starts cannot slow a run
+     * down.
+     *
+     * NetBIOS is off by default alone among them: UDP 137 is privileged, so at app tier it can
+     * only ever report `unsupported`, and shipping a listener that is guaranteed to fail as an
+     * on-by-default option would train people to ignore the status column. It stays selectable —
+     * the reason it reports is worth seeing once, and the tier that can bind it is coming.
+     */
+    fun discoveryEnabled(id: String): Boolean =
+        prefs.getBoolean("$DISCOVERY_PREFIX$id", id != DiscoveryIds.NETBIOS)
+
+    fun setDiscoveryEnabled(id: String, on: Boolean) =
+        prefs.edit().putBoolean("$DISCOVERY_PREFIX$id", on).apply()
+
+    // ---- run-duration learning ---------------------------------------------------------
+
+    /**
+     * Learned duration of one test type on THIS device, or null before the first run.
+     *
+     * The static Probe.estimatedMs values are only cold-start seeds: real durations depend on
+     * the phone and the network it stands in (ICMPv6 answers in milliseconds where IPv6 works
+     * and waits out full timeouts where it does not), so a fixed table is wrong for almost
+     * everyone almost always. What was measured last time is the only estimate that tracks
+     * reality.
+     */
+    fun learnedDurationMs(type: String): Long? =
+        prefs.getLong("$DURATION_PREFIX$type", -1L).takeIf { it > 0 }
+
+    /**
+     * Feeds one measured duration into the estimate — EMA, 70 % old / 30 % new. Heavy enough
+     * on history that a single odd run (a captive portal stalling DNS) does not whipsaw the
+     * bar, light enough that a real change (enrolling with a server un-skips three probes)
+     * converges within a few runs. Recorded whatever the test's status: a probe that skips in
+     * 2 ms will keep skipping in 2 ms until circumstances change, and then the EMA follows.
+     */
+    fun recordDurationMs(type: String, ms: Long) {
+        if (ms < 0) return
+        val key = "$DURATION_PREFIX$type"
+        val old = prefs.getLong(key, -1L)
+        val next = if (old <= 0) ms else (old * 7 + ms * 3) / 10
+        prefs.edit().putLong(key, next).apply()
+    }
+
     // ---- upload ----------------------------------------------------------------------
 
     /**
@@ -97,6 +179,41 @@ class Settings(context: Context) {
         get() = prefs.getString(SERVER_PIN, "") ?: ""
         set(v) = prefs.edit().putString(SERVER_PIN, v.trim()).apply()
 
+    /**
+     * The address the operator handed out, for showing to a person.
+     *
+     * Separate from [serverUrl], which is the endpoint actually dialled. They differ when the
+     * server publishes one public name and points devices at another to select its pinned
+     * certificate — a detail worth keeping out of the user's face but not out of the settings.
+     */
+    var serverPublicUrl: String
+        get() = (prefs.getString(SERVER_PUBLIC_URL, "") ?: "").ifBlank { serverUrl }
+        set(v) = prefs.edit().putString(SERVER_PUBLIC_URL, v.trim()).apply()
+
+    /**
+     * What the server said about itself, last time it was asked: addresses, ports, capabilities.
+     *
+     * Cached as a rendered block rather than as fields, because it is shown and never acted on —
+     * these are facts to read, not settings to apply, and storing them as settings would invite
+     * exactly the confusion of an editable box that changes nothing.
+     */
+    var serverFacts: String
+        get() = prefs.getString(SERVER_FACTS, "") ?: ""
+        set(v) = prefs.edit().putString(SERVER_FACTS, v).apply()
+
+    /**
+     * The server's own addresses, learned from its profile, for reaching it when DNS will not.
+     *
+     * Only the primaries: the alternate pair exists for NAT behaviour discovery and does not carry
+     * the control plane, so falling back to one would fail for a second, unrelated reason.
+     */
+    var serverAddrs: String
+        get() = prefs.getString(SERVER_ADDRS, "") ?: ""
+        set(v) = prefs.edit().putString(SERVER_ADDRS, v).apply()
+
+    fun serverAddrList(): List<String> =
+        serverAddrs.split(',').map { it.trim() }.filter { it.isNotEmpty() }
+
     var serverCredential: String
         get() = prefs.getString(SERVER_CRED, "") ?: ""
         set(v) = prefs.edit().putString(SERVER_CRED, v.trim()).apply()
@@ -104,6 +221,58 @@ class Settings(context: Context) {
     val serverConfigured: Boolean
         get() = serverUrl.isNotBlank() && serverPin.isNotBlank() && serverCredential.isNotBlank()
 
+    /**
+     * The DNS zone this server is authoritative for, learned from its profile.
+     *
+     * Cached because the canary probe runs at device tier, before anything has talked to the
+     * server, and a probe that had to make a control-plane call first would fail on exactly the
+     * networks worth measuring. Empty means "not known yet", and the probe reports itself as
+     * skipped rather than inventing a zone.
+     */
+    var canaryZone: String
+        get() = prefs.getString(CANARY_ZONE, "") ?: ""
+        set(v) = prefs.edit().putString(CANARY_ZONE, v.trim()).apply()
+
+    /**
+     * Host part of the configured server URL, for probes that address it directly (STUN).
+     *
+     * Derived rather than stored: a second copy of the server's name is a second thing to keep in
+     * step, and it would go stale the moment someone re-enrolled against a different server.
+     */
+    fun serverHost(): String = runCatching {
+        java.net.URI(serverUrl).host?.takeIf { it.isNotBlank() }
+    }.getOrNull() ?: ""
+
+    // ---- account ---------------------------------------------------------------------
+
+    /**
+     * The PKCE verifier and state for a sign-in that is out at the browser.
+     *
+     * Persisted rather than held in memory because handing control to a browser backgrounds this
+     * process, and Android may kill it before the callback returns. An in-memory value works on a
+     * developer's device and fails on a phone under memory pressure.
+     */
+    var pendingVerifier: String
+        get() = prefs.getString(PENDING_VERIFIER, "") ?: ""
+        set(v) = prefs.edit().putString(PENDING_VERIFIER, v).apply()
+
+    var pendingState: String
+        get() = prefs.getString(PENDING_STATE, "") ?: ""
+        set(v) = prefs.edit().putString(PENDING_STATE, v).apply()
+
+    fun clearPendingAuth() = prefs.edit().remove(PENDING_VERIFIER).remove(PENDING_STATE).apply()
+
+    /** Display name of whoever is signed in on this device; empty when nobody is. */
+    var accountName: String
+        get() = prefs.getString(ACCOUNT_NAME, "") ?: ""
+        set(v) = prefs.edit().putString(ACCOUNT_NAME, v).apply()
+
+    var accountId: String
+        get() = prefs.getString(ACCOUNT_ID, "") ?: ""
+        set(v) = prefs.edit().putString(ACCOUNT_ID, v).apply()
+
+    val signedIn: Boolean get() = accountName.isNotBlank()
+
     private fun hex(s: String) = ByteArray(s.length / 2) {
         ((Character.digit(s[it * 2], 16) shl 4) or Character.digit(s[it * 2 + 1], 16)).toByte()
     }
@@ -120,5 +289,52 @@ class Settings(context: Context) {
         const val SERVER_URL = "server_url"
         const val SERVER_PIN = "server_pin"
         const val SERVER_CRED = "server_credential"
+        const val SERVER_PUBLIC_URL = "server_public_url"
+        const val SERVER_FACTS = "server_facts"
+        const val SERVER_ADDRS = "server_addrs"
+        const val CANARY_ZONE = "server_canary_zone"
+        const val PENDING_VERIFIER = "pending_auth_verifier"
+        const val PENDING_STATE = "pending_auth_state"
+        const val ACCOUNT_NAME = "account_name"
+        const val ACCOUNT_ID = "account_id"
+        const val DURATION_PREFIX = "duration_ms."
+        const val ADB_RELAY = "adb_relay_enabled"
+        const val DISCOVERY_PREFIX = "discovery."
+        const val LONG_RUN_MINUTES = "long_run_minutes"
+    }
+}
+
+/**
+ * Ids for the selectable discovery listeners.
+ *
+ * Top-level rather than nested in [Settings] because a class gets exactly one companion object and
+ * that one is already spoken for by the preference keys, which stay private. Plain strings rather
+ * than an enum: they key a stored preference, so a listener being added or retired must not need a
+ * migration.
+ */
+object DiscoveryIds {
+    const val SSDP = "ssdp"
+    const val WSD = "wsd"
+    const val LLMNR = "llmnr"
+    const val NETBIOS = "netbios"
+
+    /** Display order: device inventory first, then the legacy name-resolution pair. */
+    val ALL = listOf(SSDP, WSD, LLMNR, NETBIOS)
+
+    fun label(id: String): String = when (id) {
+        SSDP -> "SSDP"
+        WSD -> "WS-Discovery"
+        LLMNR -> "LLMNR"
+        NETBIOS -> "NetBIOS"
+        else -> id
+    }
+
+    /** Why someone would want this one, in the few words a chip's helper line allows. */
+    fun blurb(id: String): String = when (id) {
+        SSDP -> "UPnP devices announcing themselves"
+        WSD -> "printers, scanners, cameras"
+        LLMNR -> "Windows name lookups (and that it is enabled here)"
+        NETBIOS -> "legacy Windows names — needs a privileged port, so app tier reports why not"
+        else -> ""
     }
 }

echolot-app/app/src/main/kotlin/app/echo_lot/app/SettingsScreen.kt

@@ -10,7 +10,9 @@ import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.verticalScroll
 import androidx.compose.material3.Button
@@ -19,6 +21,7 @@ import androidx.compose.material3.FilterChip
 import androidx.compose.material3.LocalContentColor
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.Surface
 import androidx.compose.material3.Switch
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
@@ -31,6 +34,7 @@ import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
 import app.echo_lot.privacy.PrivacyLevel
 
 /**
@@ -49,8 +53,14 @@ fun SettingsScreen(
     onDeleteAll: () -> Unit,
     onPreviewUpload: () -> Unit,
     onCheckServer: () -> Unit,
+    accountName: String,
+    onSignIn: () -> Unit,
+    onSignOut: () -> Unit,
     onEnroll: (String) -> Unit,
     serverStatus: String?,
+    enrollStatus: String?,
+    /** Starts or stops the adb relay service; the toggle only records the preference. */
+    onRelayChange: (Boolean) -> Unit,
     onBack: () -> Unit,
 ) {
     // SharedPreferences is not observable, so mirror each value into Compose state and write
@@ -59,13 +69,28 @@ fun SettingsScreen(
     var maxRuns by remember { mutableStateOf(settings.maxRuns.toString()) }
     var maxAgeDays by remember { mutableStateOf(settings.maxAgeDays.toString()) }
     var maxTotalMb by remember { mutableStateOf(settings.maxTotalMb.toString()) }
+    var longMinutes by remember { mutableStateOf(settings.longRunMinutes) }
     var autoUpload by remember { mutableStateOf(settings.autoUpload) }
     var privacy by remember { mutableStateOf(settings.privacyLevel) }
     var stableSalt by remember { mutableStateOf(settings.stableSalt) }
+    var relayOn by remember { mutableStateOf(settings.adbRelayEnabled) }
     var enrollLink by remember { mutableStateOf("") }
-    var serverUrl by remember { mutableStateOf(settings.serverUrl) }
+    // The public name, which is what the operator handed out and what a person recognises. The
+    // endpoint actually dialled is shown beneath it when the two differ, rather than hidden — a
+    // network engineer debugging a connection wants to see where it really goes.
+    var serverUrl by remember { mutableStateOf(settings.serverPublicUrl) }
     var serverPin by remember { mutableStateOf(settings.serverPin) }
     var serverCred by remember { mutableStateOf(settings.serverCredential) }
+    // Enrolling is asynchronous, so these are re-read when its result lands rather than when the
+    // button is pressed — reading them immediately showed the previous server's values and looked
+    // exactly like an enrollment that had silently done nothing.
+    var serverFacts by remember { mutableStateOf(settings.serverFacts) }
+    androidx.compose.runtime.LaunchedEffect(enrollStatus, serverStatus) {
+        serverFacts = settings.serverFacts
+        serverUrl = settings.serverPublicUrl
+        serverPin = settings.serverPin
+        serverCred = settings.serverCredential
+    }
 
     Column(
         Modifier.fillMaxWidth().safeDrawingPadding().verticalScroll(rememberScrollState()).padding(16.dp),
@@ -76,6 +101,39 @@ fun SettingsScreen(
             Text("Settings", style = MaterialTheme.typography.titleLarge)
         }
 
+        // ---- measurement ----
+        Card(Modifier.fillMaxWidth()) {
+            Column(Modifier.padding(14.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                Text("Long runs", style = MaterialTheme.typography.titleMedium)
+                Text(
+                    "How long a long run keeps listening. The measurements themselves take about " +
+                        "30 seconds either way; the rest of the window is spent watching for " +
+                        "things that only happen sometimes.",
+                    style = MaterialTheme.typography.bodySmall,
+                )
+                Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                    for (minutes in listOf(1, 5, 15)) {
+                        FilterChip(
+                            selected = longMinutes == minutes,
+                            onClick = { longMinutes = minutes; settings.longRunMinutes = minutes },
+                            label = { Text("$minutes min") },
+                        )
+                    }
+                }
+                Text(
+                    when (longMinutes) {
+                        1 -> "Barely longer than a quick run — enough to confirm the listeners " +
+                            "work, rarely enough to catch anything intermittent."
+                        15 -> "For a fault you already suspect and have to prove. Keep the screen " +
+                            "on and the device where the problem happens."
+                        else -> "Long enough for a link that drops every couple of minutes to do " +
+                            "it at least once, short enough to wait out."
+                    },
+                    style = MaterialTheme.typography.bodySmall,
+                )
+            }
+        }
+
         // ---- archive ----
         Card(Modifier.fillMaxWidth()) {
             Column(Modifier.padding(14.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
@@ -152,6 +210,38 @@ fun SettingsScreen(
             }
         }
 
+        // ---- account ----
+        Card(Modifier.fillMaxWidth()) {
+            Column(Modifier.padding(14.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                Text("Account", style = MaterialTheme.typography.titleMedium)
+                if (accountName.isNotBlank()) {
+                    Text("Signed in as $accountName", style = MaterialTheme.typography.bodyMedium)
+                    Text(
+                        "Runs from every device signed in to this account share one history.",
+                        style = MaterialTheme.typography.bodySmall,
+                    )
+                    TextButton(onClick = onSignOut) { Text("Sign out") }
+                } else {
+                    Text(
+                        "Signing in is optional. It links this device to an account on your " +
+                            "server, so several devices share one history — and some servers only " +
+                            "accept uploads from a signed-in device.",
+                        style = MaterialTheme.typography.bodySmall,
+                    )
+                    Button(onClick = onSignIn, enabled = settings.serverConfigured) {
+                        Text("Sign in")
+                    }
+                    if (!settings.serverConfigured) {
+                        Text(
+                            "Enrol with a server first — the account belongs to the server, not " +
+                                "to the app.",
+                            style = MaterialTheme.typography.bodySmall,
+                        )
+                    }
+                }
+            }
+        }
+
         // ---- upload ----
         Card(Modifier.fillMaxWidth()) {
             Column(Modifier.padding(14.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
@@ -183,17 +273,38 @@ fun SettingsScreen(
                     onClick = {
                         onEnroll(enrollLink)
                         enrollLink = "" // spent either way; leaving it around invites a retry
-                        serverUrl = settings.serverUrl
-                        serverPin = settings.serverPin
-                        serverCred = settings.serverCredential
                     },
                     enabled = enrollLink.isNotBlank(),
                 ) { Text("Enroll") }
+                // Beside the button that caused it. Enrolling is asynchronous, so without this the
+                // only sign of success is three fields quietly changing further down the card.
+                enrollStatus?.let {
+                    Text(it, style = MaterialTheme.typography.bodySmall)
+                }
 
                 OutlinedTextField(
-                    value = serverUrl, onValueChange = { serverUrl = it; settings.serverUrl = it },
+                    value = serverUrl,
+                    onValueChange = {
+                        serverUrl = it
+                        // Typed by hand there is no discovery to consult, so what was entered is
+                        // both the public name and the endpoint. Setting only one of them would
+                        // leave the app dialling the previous server.
+                        settings.serverUrl = it
+                        settings.serverPublicUrl = it
+                    },
                     label = { Text("Server URL") }, singleLine = true, modifier = Modifier.fillMaxWidth(),
                 )
+                // Directly under the field it explains. Anywhere else it reads as a stray sentence
+                // about some other part of the screen.
+                if (settings.serverUrl.isNotBlank() && settings.serverUrl != settings.serverPublicUrl) {
+                    Text(
+                        "Connects to ${settings.serverUrl} — this server publishes one name and " +
+                            "points devices at another, so its pinned certificate can share a port " +
+                            "with its web interface.",
+                        style = MaterialTheme.typography.bodySmall,
+                        color = LocalContentColor.current.copy(alpha = 0.7f),
+                    )
+                }
                 OutlinedTextField(
                     value = serverPin, onValueChange = { serverPin = it; settings.serverPin = it },
                     label = { Text("Certificate pin (SPKI, base64)") }, singleLine = true,
@@ -220,6 +331,52 @@ fun SettingsScreen(
                 serverStatus?.let {
                     Text(it, style = MaterialTheme.typography.bodySmall)
                 }
+                // What the server reported, placed under the button that asks it rather than among
+                // the fields above: these are facts to read, not settings to apply, and an
+                // editable-looking box that changes nothing is worse than no box at all.
+                //
+                // Monospaced so the addresses line up under each other — column alignment is most
+                // of what makes a list of IPs quicker to read than prose.
+                if (serverFacts.isNotBlank()) {
+                    Surface(
+                        color = MaterialTheme.colorScheme.surfaceVariant,
+                        shape = RoundedCornerShape(8.dp),
+                        modifier = Modifier.fillMaxWidth(),
+                    ) {
+                        Column(
+                            Modifier.padding(horizontal = 12.dp, vertical = 10.dp),
+                            verticalArrangement = Arrangement.spacedBy(2.dp),
+                        ) {
+                            Text(
+                                "WHAT THIS SERVER REPORTS",
+                                style = MaterialTheme.typography.labelSmall,
+                                color = LocalContentColor.current.copy(alpha = 0.7f),
+                            )
+                            // Real columns rather than padded text: the label column has a fixed
+                            // width, so values line up whatever the font does, and a long value
+                            // wraps inside its own column instead of under the labels.
+                            for (line in serverFacts.lines()) {
+                                val label = line.substringBefore('|')
+                                val value = line.substringAfter('|', "")
+                                Row(Modifier.fillMaxWidth()) {
+                                    Text(
+                                        label,
+                                        style = MaterialTheme.typography.bodySmall,
+                                        color = LocalContentColor.current.copy(alpha = 0.7f),
+                                        modifier = Modifier.width(72.dp),
+                                    )
+                                    Text(
+                                        value,
+                                        style = MaterialTheme.typography.bodySmall.copy(
+                                            fontFamily = FontFamily.Monospace,
+                                        ),
+                                        modifier = Modifier.weight(1f),
+                                    )
+                                }
+                            }
+                        }
+                    }
+                }
                 Text(
                     "This app is ${BuildConfig.APP_SEMVER} and speaks probe protocol " +
                         "${app.echo_lot.protocol.Compat.PROTOCOL_VERSION}. It works with servers " +
@@ -228,6 +385,40 @@ fun SettingsScreen(
                 )
             }
         }
+
+        // ---- dev relay ------------------------------------------------------------------
+        //
+        // Debug builds only, and duplicated as a switch on the home screen because that is where
+        // it is reached for. It publishes where this device can be reached over adb: scaffolding
+        // for driving a test device, useless without wireless debugging, and not something a
+        // release build should offer at all.
+        if (BuildConfig.DEBUG) Card(Modifier.fillMaxWidth()) {
+            Column(Modifier.padding(16.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                Text("Developer relay", style = MaterialTheme.typography.titleMedium)
+                Toggle(
+                    label = "Relay this device's adb endpoint",
+                    detail = "Watches adbd's own mDNS announcement and reports host:port to the " +
+                        "enrolled server, so a developer on another network can reach this " +
+                        "device — mDNS does not cross subnets, and the port rotates every few " +
+                        "minutes. Runs in the foreground with a notification while on.",
+                    checked = relayOn,
+                    enabled = settings.serverConfigured,
+                    onChange = { on ->
+                        relayOn = on
+                        settings.adbRelayEnabled = on
+                        onRelayChange(on)
+                    },
+                )
+                if (!settings.serverConfigured) {
+                    Text(
+                        "Needs an enrolled server: the report is authenticated with this " +
+                            "device's credential.",
+                        style = MaterialTheme.typography.bodySmall,
+                        color = LocalContentColor.current.copy(alpha = 0.7f),
+                    )
+                }
+            }
+        }
         Spacer(Modifier.height(24.dp))
     }
 }

echolot-app/core-engine/src/main/kotlin/app/echo_lot/engine/DownstreamMeasurement.kt

@@ -168,6 +168,10 @@ class DownstreamMeasurement(private val ids: IdSource) {
         trainCount: Int = 100,
         trainSizeBytes: Int = 300,
         trainIntervalUs: Int = 3_000,
+        // DSCP to mark the train with (0-63), or -1 to leave packets unmarked. Pairing a marked
+        // downtrain with the server-observed DSCP of an upstream train is the two-direction
+        // sec.dscp_ecn_survival measurement.
+        trainDscp: Int = -1,
     ): Pair<List<Test>, List<Finding>> {
         val tests = ArrayList<Test>()
         val findings = ArrayList<Finding>()
@@ -175,7 +179,8 @@ class DownstreamMeasurement(private val ids: IdSource) {
         val df = bigSend(credential, sessionId, control, probe, sessionRef, sizes, df = true)
         val frag = bigSend(credential, sessionId, control, probe, sessionRef, sizes, df = false)
         val train = downTrain(
-            credential, sessionId, control, probe, sessionRef, trainCount, trainSizeBytes, trainIntervalUs,
+            credential, sessionId, control, probe, sessionRef, trainCount, trainSizeBytes,
+            trainIntervalUs, trainDscp,
         )
 
         tests.add(df.test); tests.add(frag.test); tests.add(train.test)
@@ -338,15 +343,19 @@ class DownstreamMeasurement(private val ids: IdSource) {
 
     private fun downTrain(
         credential: String, sessionId: String, control: ControlClient, probe: ProbeSession,
-        sessionRef: String, count: Int, sizeBytes: Int, intervalUs: Int,
+        sessionRef: String, count: Int, sizeBytes: Int, intervalUs: Int, dscp: Int = -1,
     ): TrainResult {
         val testId = ids.uuid()
         val started = ids.monoNs()
 
+        // dscp is only sent when requested: an older server rejects unknown-value problems
+        // louder than absent keys, and unmarked is the correct default for a plain loss train.
+        val dscpField = if (dscp in 0..63) ""","dscp":$dscp""" else ""
         val reply = runCatching {
             control.action(
                 credential, sessionId,
-                """{"action":"downtrain","count":$count,"size_bytes":$sizeBytes,"interval_us":$intervalUs}""",
+                """{"action":"downtrain","count":$count,"size_bytes":$sizeBytes,""" +
+                    """"interval_us":$intervalUs$dscpField}""",
             )
         }
         if (reply.isFailure) {
@@ -394,6 +403,12 @@ class DownstreamMeasurement(private val ids: IdSource) {
                 interArrivalMsAvg = interArrival.average().takeIf { interArrival.isNotEmpty() }?.let(::round1),
                 interArrivalMsMax = interArrival.maxOrNull()?.let(::round1),
                 sendIntervalUs = intervalUs,
+                dscpRequested = dscp.takeIf { it in 0..63 },
+                // The server says whether it could actually mark (dscp_applied); recorded so a
+                // survival comparison never blames the path for a marking the sender skipped.
+                dscpApplied = reply.getOrNull()?.let {
+                    Regex("\"dscp_applied\"\\s*:\\s*(true|false)").find(it)?.groupValues?.get(1)?.toBoolean()
+                },
             ),
         ) as JsonObject
 
@@ -490,4 +505,6 @@ data class DownTrainMetrics(
     @SerialName("inter_arrival_ms_avg") val interArrivalMsAvg: Double? = null,
     @SerialName("inter_arrival_ms_max") val interArrivalMsMax: Double? = null,
     @SerialName("send_interval_us") val sendIntervalUs: Int,
+    @SerialName("dscp_requested") val dscpRequested: Int? = null,
+    @SerialName("dscp_applied") val dscpApplied: Boolean? = null,
 )

echolot-app/core-engine/src/main/kotlin/app/echo_lot/engine/ServerMeasurement.kt

@@ -88,6 +88,14 @@ class ServerMeasurement(
             tests.add(test)
             allFindings.addAll(findings)
 
+            // The upstream train needs no grant and no capability beyond udp-probe itself; a
+            // server that predates trains simply never answers the report request, which the
+            // measurement reports as exactly that ambiguity rather than as network loss.
+            val (utTest, utFindings) = UpstreamTrainMeasurement(ids)
+                .run(ps, sessionRef = "sess-1")
+            tests.add(utTest)
+            allFindings.addAll(utFindings)
+
             // Downstream needs a session the server has already seen traffic from — the echo
             // train just provided that — and a server that advertises the grants. Skipped
             // quietly against an older server rather than reported as a failure of the network.

echolot-app/core-engine/src/main/kotlin/app/echo_lot/engine/UpstreamTrainMeasurement.kt

@@ -0,0 +1,159 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.engine
+
+import app.echo_lot.measurement.*
+import app.echo_lot.protocol.ProbeSession
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.encodeToJsonElement
+
+/**
+ * train.udp_updown — the client sends a paced train (types 0x03), then asks the server what
+ * arrived (0x04 → 0x05) and lines both views up per sequence number.
+ *
+ * This is the measurement a round trip cannot make: an echo run only says "lost somewhere", the
+ * train's two ledgers say lost on the way OUT, specifically, because the server's report names
+ * exactly which sequence numbers reached it. The downstream direction has its own test
+ * (train.udp_downstream) under a grant; this one needs none, since the client generates all the
+ * traffic itself.
+ *
+ * The evidence is the schema's columnar TrainEvidence: one index per sent packet, with the
+ * server-side columns null where a packet never arrived. Server timestamps are on the server's
+ * own clock — only differences within that clock mean anything unless time.server_offset maps
+ * them (two-clock rule).
+ */
+class UpstreamTrainMeasurement(private val ids: IdSource) {
+
+    private val json = Json { encodeDefaults = true; explicitNulls = true }
+
+    fun run(
+        probe: ProbeSession,
+        sessionRef: String,
+        count: Int = 200,
+        sizeBytes: Int = 200,
+        interPacketMs: Long = 5,
+    ): Pair<Test, List<Finding>> {
+        val testId = ids.uuid()
+        val started = ids.monoNs()
+        // The id only needs to be unique within this session; a clash across sessions is
+        // meaningless because trains are buffered per session on the server.
+        val trainId = (System.nanoTime() and 0x7FFFFFFF).toInt()
+
+        val sent = probe.sendTrain(trainId, count, sizeBytes, interPacketMs)
+        // Let the tail arrive before asking for the ledger; packets still in flight when the
+        // report is cut would read as upstream loss.
+        Thread.sleep(300)
+        val report = probe.trainReport(trainId)
+
+        if (report == null) {
+            return Test(
+                id = testId, type = TestType.TRAIN_UDP_UPDOWN, sessionRef = sessionRef,
+                tier = Tier.APP, startedMonoNs = started, endedMonoNs = ids.monoNs(),
+                status = TestStatus.FAILED,
+                // Honest ambiguity: an old server drops 0x04 silently, and a lost report looks
+                // identical from here. Neither says anything about the train itself.
+                error = TestError(
+                    "no_report",
+                    "no train report arrived — the report was lost, or the server predates trains",
+                ),
+            ) to emptyList()
+        }
+
+        val bySeq = report.rows.associateBy { it.seq }
+        fun col255(v: Int): Int? = v.takeIf { it != 255 } // 255 = "not observed" on the wire
+
+        val evidence = TrainEvidence(
+            epochMonoNs = started,
+            seq = sent.map { it.seq },
+            tTxNs = sent.map { it.tTxNs },
+            tSrvRxNs = sent.map { bySeq[it.seq]?.tRxNs },
+            tRxNs = sent.map { null }, // upstream only: nothing comes back per packet
+            sizeBytes = sent.map { it.sizeBytes },
+            ttlSeenByServer = sent.map { bySeq[it.seq]?.let { r -> col255(r.ttl) } },
+            dscpSeenByServer = sent.map { bySeq[it.seq]?.let { r -> col255(r.dscp) } },
+            ecnSeenByServer = sent.map { bySeq[it.seq]?.let { r -> col255(r.ecn) } },
+            evidenceTruncated = report.truncated,
+        ).toEvidence()
+
+        // Loss against the server's total count, not its row list: rows past the server's buffer
+        // cap are counted but not kept, and treating them as lost would invent loss exactly on
+        // the biggest trains.
+        val lossPct = if (sent.isEmpty()) 0.0 else {
+            (sent.size - report.received).coerceAtLeast(0) * 100.0 / sent.size
+        }
+        val metrics = json.encodeToJsonElement(
+            UpstreamTrainMetrics(
+                sent = sent.size,
+                receivedByServer = report.received,
+                lossPct = round1(lossPct),
+                reportPartsExpected = report.partsExpected,
+                reportPartsReceived = report.partsReceived,
+                truncated = report.truncated,
+            ),
+        ) as JsonObject
+
+        val findings = ArrayList<Finding>()
+        if (sent.isNotEmpty() && report.received == 0) {
+            findings.add(
+                Finding(
+                    id = ids.uuid(),
+                    code = FindingRegistry.UDP_UNREACHABLE_UPSTREAM.code,
+                    category = FindingRegistry.UDP_UNREACHABLE_UPSTREAM.category,
+                    severity = FindingRegistry.UDP_UNREACHABLE_UPSTREAM.severity,
+                    confidence = Confidence.HIGH,
+                    title = "The server received none of ${sent.size} upstream packets",
+                    description = "Every train packet vanished on the way out, while the " +
+                        "report request's reply made it back — the outbound path drops this " +
+                        "traffic, the return path works.",
+                    evidenceRefs = listOf(EvidenceRef(testId)),
+                ),
+            )
+        } else if (lossPct >= 2.0) {
+            findings.add(
+                Finding(
+                    id = ids.uuid(),
+                    code = FindingRegistry.LOSS_UPSTREAM.code,
+                    category = FindingRegistry.LOSS_UPSTREAM.category,
+                    severity = FindingRegistry.LOSS_UPSTREAM.severity,
+                    confidence = Confidence.HIGH,
+                    title = "Upstream loss of ${round1(lossPct)} %",
+                    description = "The server received ${report.received} of the ${sent.size} " +
+                        "packets this device sent, and its per-sequence ledger names the " +
+                        "missing ones. This is outbound loss specifically; the return path " +
+                        "delivered the report.",
+                    evidenceRefs = listOf(EvidenceRef(testId)),
+                ),
+            )
+        }
+
+        val status = when {
+            report.received == 0 && sent.isNotEmpty() -> TestStatus.FAILED
+            report.partsReceived < report.partsExpected -> TestStatus.PARTIAL
+            else -> TestStatus.OK
+        }
+        return Test(
+            id = testId, type = TestType.TRAIN_UDP_UPDOWN, sessionRef = sessionRef, tier = Tier.APP,
+            startedMonoNs = started, endedMonoNs = ids.monoNs(),
+            status = status, evidence = evidence, metrics = metrics,
+        ) to findings
+    }
+
+    private fun round1(v: Double) = Math.round(v * 10.0) / 10.0
+}
+
+/** Metrics for train.udp_updown. */
+@Serializable
+data class UpstreamTrainMetrics(
+    val sent: Int,
+    /** The server's total count — includes packets past its row buffer (counted, not listed). */
+    @SerialName("received_by_server") val receivedByServer: Int,
+    @SerialName("loss_pct") val lossPct: Double,
+    @SerialName("report_parts_expected") val reportPartsExpected: Int,
+    @SerialName("report_parts_received") val reportPartsReceived: Int,
+    /** The server's row buffer overflowed: rows are a sample, the count is still complete. */
+    val truncated: Boolean,
+)

echolot-app/core-engine/src/test/kotlin/app/echo_lot/engine/LiveUpstreamTrainTest.kt

@@ -0,0 +1,65 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.engine
+
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.protocol.ControlClient
+import app.echo_lot.protocol.ProbeSession
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+import kotlin.test.assertTrue
+
+/**
+ * Upstream train (types 0x03-0x05) against a LIVE server. Self-skips without ECHOLOT_LIVE_*.
+ *
+ * What is asserted is the ledger property: the server's report must account for what was sent,
+ * per sequence number, because directional loss attribution is the entire reason trains exist —
+ * a test that only checked "a report came back" would pass against a server that counts nothing.
+ */
+class LiveUpstreamTrainTest {
+
+    private val url = System.getenv("ECHOLOT_LIVE_URL")
+    private val pin = System.getenv("ECHOLOT_LIVE_PIN")
+    private val cred = System.getenv("ECHOLOT_LIVE_CRED")
+    private val udp = System.getenv("ECHOLOT_LIVE_UDP")
+    private val target = System.getenv("ECHOLOT_LIVE_TARGET") ?: "fmr"
+
+    @Test
+    fun serverLedgerAccountsForTheTrain() {
+        if (url == null || pin == null || cred == null || udp == null) {
+            println("LiveUpstreamTrainTest skipped (no ECHOLOT_LIVE_* env)"); return
+        }
+        val control = ControlClient(url, setOf(pin), "0.2.0")
+        val session = control.createSession(cred, target)
+        val (host, port) = udp.split(":").let { it[0] to it[1].toInt() }
+
+        val (test, findings) = ProbeSession(cred, session, host, port).use { ps ->
+            ps.echo() // prime the session so its source is known
+            UpstreamTrainMeasurement(SystemIdSource()).run(
+                ps, sessionRef = "sess-1", count = 120, sizeBytes = 200, interPacketMs = 3,
+            )
+        }
+        control.deleteSession(cred, session.sessionId)
+
+        val m = assertNotNull(test.metrics).toString()
+        println("updown: ${test.status} $m")
+        for (f in findings) println("finding ${f.code} [${f.severity}] ${f.title}")
+
+        assertEquals(TestStatus.OK, test.status, "train report incomplete or absent: $m")
+
+        val sent = Regex(""""sent":(\d+)""").find(m)?.groupValues?.get(1)?.toInt()
+        val received = Regex(""""received_by_server":(\d+)""").find(m)?.groupValues?.get(1)?.toInt()
+        assertNotNull(sent); assertNotNull(received)
+        assertTrue(sent > 0, "nothing was sent: $m")
+        // Over a working path the ledger must be near-complete; a lossy wifi may drop a few, but
+        // a server that fails to count would show up as massive phantom loss here.
+        assertTrue(received >= sent * 9 / 10, "server counted $received of $sent: $m")
+
+        // The columnar evidence must carry a server timestamp for arrived packets — that column
+        // is what one-way delay math consumes after timesync.
+        val ev = assertNotNull(test.evidence).toString()
+        assertTrue(ev.contains("t_srv_rx_ns"), "no server rx column in evidence")
+    }
+}

echolot-app/core-measurement/src/main/kotlin/app/echo_lot/measurement/Document.kt

@@ -28,6 +28,7 @@ data class MeasurementDocument(
 data class Run(
     val id: String, // UUIDv7
     val trigger: Trigger,
+    val mode: RunMode = RunMode.SHORT,
     @SerialName("started_at") val startedAt: String, // RFC3339 UTC, human correlation only
     @SerialName("ended_at") val endedAt: String? = null,
     val clock: Clock,
@@ -35,9 +36,58 @@ data class Run(
     val device: DeviceInfo,
     val tiers: Tiers,
     @SerialName("profiles_used") val profilesUsed: List<String> = emptyList(),
+    val constraints: Constraints = Constraints(),
     val notes: String? = null,
 )
 
+/**
+ * What limited this run — the counterpart to [Tiers], which records what was available.
+ *
+ * A constrained run is not a failed run, and it is not a normal one either. Without this, a run
+ * taken through a VPN looks exactly like a clean run of a healthy network: the same shape, the
+ * same green verdict, and no way for a reader — or a server aggregating thousands of these — to
+ * know that almost nothing was actually measured.
+ */
+@Serializable
+data class Constraints(
+    /** A VPN held the default route while this ran. */
+    @SerialName("vpn_active") val vpnActive: Boolean = false,
+    /**
+     * Per-network probing was refused by the OS.
+     *
+     * Android blocks `Network.bindSocket()` on the underlying networks whenever a VPN is up, to
+     * stop apps leaking around the tunnel. Every per-network test then measures nothing, so any
+     * conclusion drawn about the wifi or cellular link underneath is unfounded.
+     */
+    @SerialName("per_network_blocked") val perNetworkBlocked: Boolean = false,
+    /** Networks that could not be measured, by id. */
+    @SerialName("unmeasured_networks") val unmeasuredNetworks: List<String> = emptyList(),
+) {
+    /** True when this run's results mean something different from an unconstrained one. */
+    val constrained: Boolean get() = vpnActive || perNetworkBlocked
+}
+
+/**
+ * How long the run watched the network — and therefore what its silence is worth.
+ *
+ * A [SHORT] run is a sequence of one-shot probes: each looks at the network for a second or two and
+ * moves on. That is enough to characterise a network's *configuration*, and it is structurally
+ * incapable of seeing anything intermittent. A wifi link that drops for four seconds every two
+ * minutes, a resolver that stalls under load, an AP that roams — none of these leave a trace in
+ * thirty seconds of probing unless the run happened to coincide with one.
+ *
+ * A [LONG] run starts continuous listeners at t=0, runs the same battery beside them, and keeps
+ * sampling until the window closes. It answers a different question, so a reader must not treat the
+ * two alike: **the mode is what licenses an argument from absence**. "No drops were observed" means
+ * something after five minutes of watching and nothing at all after a thirty-second run, and
+ * without this field the two documents are indistinguishable.
+ */
+@Serializable
+enum class RunMode {
+    @SerialName("short") SHORT,
+    @SerialName("long") LONG,
+}
+
 @Serializable
 enum class Trigger {
     @SerialName("manual") MANUAL,

echolot-app/core-measurement/src/main/kotlin/app/echo_lot/measurement/FindingRegistry.kt

@@ -103,6 +103,26 @@ object FindingRegistry {
         "Android's own connectivity checks fail on this network.",
     )
 
+    /**
+     * The finding a short run cannot make.
+     *
+     * Every one-shot probe describes the network during its own two seconds. A link that drops and
+     * returns between two of them leaves no trace anywhere in the document — the probes before and
+     * after both succeed, and the run reports a healthy network. Only a listener that watches the
+     * whole window sees the gap, which is why this is emitted from `networks[].changes[]` (§4)
+     * rather than from any test's evidence.
+     *
+     * MEDIUM by default and escalated by the emitter on repeat: one drop in five minutes is worth
+     * knowing about, three is the difference between "the wifi hiccuped" and "this link is why
+     * calls keep dropping". Deliberately claims a *completed* cycle — lost and then regained — so
+     * it never fires for a network that was simply turned off partway through the run.
+     */
+    val LINK_FLAPPING = FindingSpec(
+        "connectivity.link_flapping", Category.CONNECTIVITY, Severity.MEDIUM,
+        "A network dropped and came back one or more times during the run.",
+        rulesOut = "A momentary probe failure: the drop was watched happening, not inferred from silence.",
+    )
+
     // ---- mtu -------------------------------------------------------------------------
 
     val MTU_REDUCED_DOWNSTREAM = FindingSpec(
@@ -169,10 +189,125 @@ object FindingRegistry {
     // they silently rolled up under connectivity: the third instance of a prefix disagreeing with
     // its category and quietly moving a fault to a different verdict light.
 
+    /**
+     * Renamed from `v6.broken`, which claimed more than the evidence supports.
+     *
+     * The only signal behind it is ICMPv6 echo getting no reply — and ICMPv6 echo is widely
+     * filtered on networks where IPv6 otherwise works perfectly. A phone that reported this while
+     * happily loading an IPv6-only site over TCP is what caught it. From here the two cases look
+     * identical, so the finding now says what was observed and names both explanations rather than
+     * picking one.
+     *
+     * It is worth reporting either way: filtered ICMPv6 breaks Path MTU Discovery, which is its
+     * own fault even when IPv6 works.
+     */
+    /**
+     * A global IPv6 address with no default route.
+     *
+     * This is the structural version of the same complaint, and it is worth far more than the
+     * ICMP one because it admits no other explanation: the device has an address it cannot route
+     * with. Nothing is filtered, nothing is inferred — the routing table says so directly, and it
+     * is already in the link snapshot.
+     *
+     * Not always a fault. A VPN that installs host routes to specific destinations produces
+     * exactly this shape on purpose, and it works. What makes it worth reporting either way is
+     * that applications cannot tell: having a global address, they will try IPv6 first and stall
+     * for every destination the routes do not cover.
+     */
+    /**
+     * An IPv6 default route with no global address to use it from — the mirror of
+     * [V6_NO_DEFAULT_ROUTE], and the more common misconfiguration of the two.
+     *
+     * The router is sending RAs that name it as a default gateway, but SLAAC produced no address:
+     * no prefix information option, or a prefix without the autonomous flag, or DHCPv6-only
+     * addressing the device did not complete. The network is announcing IPv6 service it does not
+     * actually deliver.
+     *
+     * This is worth flagging above the ICMP signal because it is both certain and consequential.
+     * Hosts see router advertisements, believe IPv6 is available, and pay a connection-attempt
+     * timeout on every dual-stack destination before falling back to IPv4 — the classic "the
+     * internet feels slow" complaint with no packet loss anywhere to explain it.
+     */
+    val V6_ROUTE_WITHOUT_ADDRESS = FindingSpec(
+        "v6.route_without_address", Category.IPV6, Severity.MEDIUM,
+        "The network advertises an IPv6 default route but the device has no global IPv6 address.",
+        rulesOut = "A working IPv6 setup: SLAAC did not produce a usable address on this link.",
+    )
+
+    /**
+     * A VPN prevented the underlying networks from being measured.
+     *
+     * Reported rather than worked around: Android refuses `Network.bindSocket()` on the networks
+     * beneath a VPN precisely so apps cannot leak around the tunnel, and that is correct
+     * behaviour. What is not acceptable is a run that quietly measures nothing and calls the
+     * result healthy, so this says plainly which networks went unmeasured and why.
+     */
+    /**
+     * The network's DNS server answers, but this device cannot resolve through it.
+     *
+     * Worth separating from every other DNS failure because the remedy is somewhere else entirely.
+     * A name that will not resolve looks identical to a user whatever the cause, and the two causes
+     * pull in opposite directions: a server that does not answer means the network is broken and
+     * the router is the thing to examine, while a server that answers a direct query on a device
+     * that still cannot resolve means the platform resolver has wedged — fixed by toggling wifi,
+     * and nothing to do with the network at all.
+     *
+     * Proven rather than inferred: the probe sends its own UDP query, bypassing the component under
+     * suspicion, and compares that against what the platform returns for the same name.
+     */
+    /**
+     * The network hands out a search domain its DNS server will not answer for.
+     *
+     * A resolver appends search domains to lookups, so every name a client asks about can stall on
+     * a domain the server ignores. The failure mode is silence rather than a negative answer, and
+     * silence is indistinguishable from packet loss: clients retry instead of moving on, and some
+     * give up on the lookup entirely. That makes it look like the device is broken when the
+     * network is.
+     *
+     * Whether it bites depends on the resolver — some try the bare name first and never notice —
+     * which is why two devices on the same network can disagree about whether DNS works.
+     */
+    val DNS_SEARCH_DOMAIN_UNANSWERED = FindingSpec(
+        "dns.search_domain_unanswered", Category.DNS, Severity.HIGH,
+        "The network advertises a DNS search domain that its own server does not answer for.",
+        rulesOut = "A fault on this device: the same server answers ordinary names normally.",
+    )
+
+    val DNS_SYSTEM_RESOLVER_BROKEN = FindingSpec(
+        "dns.system_resolver_broken", Category.DNS, Severity.HIGH,
+        "The network's DNS server answers, but this device cannot resolve names through it.",
+        rulesOut = "A network fault: the server replied to a query sent from this device.",
+    )
+
+    val MEASUREMENT_VPN_CONSTRAINED = FindingSpec(
+        "measurement.vpn_constrained", Category.CONNECTIVITY, Severity.INFO,
+        "A VPN was active, so the networks underneath it could not be measured.",
+        rulesOut = "Nothing — this run says little about the underlying network either way.",
+    )
+
+    val V6_NO_DEFAULT_ROUTE = FindingSpec(
+        "v6.no_default_route", Category.IPV6, Severity.MEDIUM,
+        "The device has a global IPv6 address but no IPv6 default route.",
+        rulesOut = "Guesswork: this is read from the routing table, not inferred from silence.",
+    )
+
+    val V6_NO_ICMP_REPLY = FindingSpec(
+        "v6.no_icmp_reply", Category.IPV6, Severity.LOW,
+        "IPv6 is configured but ICMPv6 echo gets no reply.",
+        rulesOut = "Nothing on its own: IPv6 may work fine with ICMP filtered.",
+    )
+
+    /**
+     * IPv6 is advertised and does not work — the claim `v6.broken` originally made on ICMP
+     * silence alone, now reinstated because it can finally be backed: it is only emitted when a
+     * real IPv6 TCP connection (v6.brokenness) failed on the same network whose ICMPv6 went
+     * unanswered. Two independent transports failing on a network that advertises IPv6 is what
+     * "broken" actually means; either signal alone still gets [V6_NO_ICMP_REPLY].
+     */
     val V6_BROKEN = FindingSpec(
-        "v6.broken", Category.IPV6, Severity.MEDIUM,
-        "IPv6 is configured on this network but does not work.",
-        rulesOut = "Absence of IPv6: it is provisioned, it simply fails.",
+        "v6.broken", Category.IPV6, Severity.HIGH,
+        "IPv6 is advertised on this network but carries no traffic.",
+        rulesOut = "ICMP filtering as the benign explanation: a TCP connection over IPv6 failed too.",
     )
 
     /**
@@ -190,13 +325,14 @@ object FindingRegistry {
     /** Every registered finding, in declaration order. */
     val all: List<FindingSpec> = listOf(
         UDP_UNREACHABLE, UDP_UNREACHABLE_UPSTREAM, UDP_LOSS, LOSS_UPSTREAM, LOSS_DOWNSTREAM,
-        DOWNSTREAM_BLOCKED, DOWNSTREAM_REORDER, CAPTIVE_PORTAL, NO_INTERNET,
+        DOWNSTREAM_BLOCKED, DOWNSTREAM_REORDER, CAPTIVE_PORTAL, NO_INTERNET, LINK_FLAPPING,
         MTU_REDUCED_DOWNSTREAM, MTU_DOWNSTREAM_BLACKHOLE, FRAGMENTS_BLOCKED,
         FRAGMENT_REORDER_SENSITIVE,
         NAT_UDP_REBINDING, NAT_SYMMETRIC,
         THROUGHPUT_NO_DELIVERY, THROUGHPUT_BELOW_OFFERED,
         DNS_ANSWER_REWRITTEN, DNS_AUTHORITATIVE_UNREACHABLE,
-        V6_BROKEN, V6_NOT_OFFERED,
+        DNS_SEARCH_DOMAIN_UNANSWERED, DNS_SYSTEM_RESOLVER_BROKEN, MEASUREMENT_VPN_CONSTRAINED,
+        V6_NO_DEFAULT_ROUTE, V6_ROUTE_WITHOUT_ADDRESS, V6_NO_ICMP_REPLY, V6_BROKEN, V6_NOT_OFFERED,
     )
 
     private val byCode: Map<String, FindingSpec> = all.associateBy { it.code }

echolot-app/core-measurement/src/main/kotlin/app/echo_lot/measurement/Network.kt

@@ -18,6 +18,39 @@ data class Network(
     val wifi: Wifi? = null,
     val cellular: Cellular? = null,
     val changes: List<NetworkChange> = emptyList(),
+    @SerialName("system_verdict") val systemVerdict: SystemVerdict? = null,
+    /**
+     * Whether an ordinary app may send on this network at all.
+     *
+     * False for the carrier's special-purpose networks — IMS/VoLTE, MMS, XCAP — which appear
+     * beside the real ones in Android's list and carry neither `INTERNET` nor `NOT_RESTRICTED`.
+     * Binding to those needs `CONNECTIVITY_USE_RESTRICTED_NETWORKS`, a privileged permission no
+     * normal app can hold, so the refusal is permanent and says nothing about the network's
+     * health. Recorded rather than hidden: a reader seeing an interface with no measurements
+     * against it deserves to know the OS forbade them, instead of concluding the link is dead.
+     */
+    @SerialName("app_usable") val appUsable: Boolean? = null,
+)
+
+/**
+ * What Android itself concluded about a network, as opposed to what we measured.
+ *
+ * Recorded because it is the verdict the user can see — the "no internet" warning in the status
+ * bar — and because it is free: the platform has already done the work by the time a run starts.
+ *
+ * Its real value is disagreement. When Android says a network is unusable and our own probes reach
+ * the internet regardless, the fault is in the device rather than the network, and that distinction
+ * is the difference between "fix your router" and "toggle your wifi". Neither number alone can say
+ * that; only the two together.
+ */
+@Serializable
+data class SystemVerdict(
+    /** Android's own connectivity check passed. Null when the platform did not say. */
+    val validated: Boolean? = null,
+    /** Android believes a captive portal is intercepting this network. */
+    @SerialName("captive_portal") val captivePortal: Boolean? = null,
+    /** Some traffic works and some does not — Android's own hedge. */
+    @SerialName("partial_connectivity") val partialConnectivity: Boolean? = null,
 )
 
 @Serializable
@@ -111,3 +144,38 @@ data class NetworkChange(
     val kind: String, // lost | gained | link_changed
     val detail: JsonObject? = null,
 )
+
+/**
+ * What a network's `changes[]` add up to.
+ *
+ * Lives beside the type rather than in the collector that produces it because two independent
+ * consumers ask the same question — the watcher, computing its metrics, and the run engine,
+ * deciding whether to emit `connectivity.link_flapping` — and a document whose metric and finding
+ * disagreed about how many times the link dropped would be worse than one reporting neither.
+ */
+object NetworkChanges {
+
+    const val LOST = "lost"
+    const val GAINED = "gained"
+    const val LINK_CHANGED = "link_changed"
+
+    /**
+     * Completed drop-and-return cycles: a `lost` with a later `gained` on the same network.
+     *
+     * A cycle has to *complete*. A link that goes away at minute four and is still gone when the
+     * window closes was not flapping — it was switched off, or the device was carried out of
+     * range, and calling that the same fault would put a phone in a lift beside a failing access
+     * point.
+     */
+    fun flapCycles(kinds: List<String>): Int {
+        var cycles = 0
+        var down = false
+        for (k in kinds) {
+            if (k == LOST) down = true
+            else if (k == GAINED && down) { cycles++; down = false }
+        }
+        return cycles
+    }
+
+    fun flapCyclesOf(changes: List<NetworkChange>): Int = flapCycles(changes.map { it.kind })
+}

echolot-app/core-measurement/src/main/kotlin/app/echo_lot/measurement/Summary.kt

@@ -35,6 +35,9 @@ data class CategorySummary(
  *   (critical|high → red, medium|low → yellow, info/none → green).
  * - A category is `inconclusive` when > 50% of its tests are failed/unsupported.
  * - Overall = the worst category light; `inconclusive` only when ALL categories are.
+ * - A run whose per-network probing was blocked is `inconclusive` outright, whatever the
+ *   categories say. The lights describe what the tests found; when the OS refused to let the
+ *   tests run, a green light would describe nothing at all.
  *
  * The mapping test-type → category comes from [TestType.category]. Only categories that have
  * findings or tests appear in the summary.
@@ -44,7 +47,10 @@ object Verdicts {
     private fun isInconclusiveTest(s: TestStatus) =
         s == TestStatus.FAILED || s == TestStatus.UNSUPPORTED
 
-    fun derive(tests: List<Test>, findings: List<Finding>): Summary {
+    fun derive(tests: List<Test>, findings: List<Finding>): Summary =
+        derive(tests, findings, Constraints())
+
+    fun derive(tests: List<Test>, findings: List<Finding>, constraints: Constraints): Summary {
         val testsByCat = tests.groupBy { TestType.category(it.type) }
         val findingsByCat = findings.groupBy { it.category }
         val categories = (testsByCat.keys + findingsByCat.keys)
@@ -72,7 +78,14 @@ object Verdicts {
             )
         }
 
-        val overall = deriveOverall(perCat.values)
+        // A run that could not measure the networks it was asked about has not found them
+        // healthy; it has found out nothing. Reporting that as green is the single most
+        // misleading thing this function could do, so the constraint outranks the lights.
+        val overall = if (constraints.perNetworkBlocked) {
+            Verdict.INCONCLUSIVE
+        } else {
+            deriveOverall(perCat.values)
+        }
         return Summary(overall = overall, categories = perCat)
     }
 

echolot-app/core-measurement/src/main/kotlin/app/echo_lot/measurement/Test.kt

@@ -89,6 +89,13 @@ object TestType {
     // dns
     const val DNS_RESOLVER_INVENTORY = "dns.resolver_inventory"
     const val DNS_CANARY = "dns.canary"
+    /**
+     * Does this device's own resolver work, as distinct from the network's DNS.
+     *
+     * Registry addition, v1.1. Kept apart from [DNS_CANARY], which asks whether answers are being
+     * tampered with; this asks whether answers arrive at all, and where the failure sits.
+     */
+    const val DNS_RESOLVER = "dns.resolver"
     const val DNS_INTERCEPTION = "dns.interception"
     const val DNS_TTL_INTEGRITY = "dns.ttl_integrity"
     const val DNS_ANSWER_INTEGRITY = "dns.answer_integrity"
@@ -126,6 +133,16 @@ object TestType {
     const val LOCAL_MDNS_INVENTORY = "local.mdns_inventory"
     const val LOCAL_SSDP_INVENTORY = "local.ssdp_inventory"
     const val LOCAL_LLMNR_INVENTORY = "local.llmnr_inventory"
+    /**
+     * WS-Discovery (UDP 3702) and NetBIOS name service (UDP 137). Registry additions, v1.2.
+     *
+     * Both are passive: the traffic is broadcast to the segment whether or not anyone asks, so
+     * listening is the whole measurement. They earn their own ids rather than folding into
+     * [LOCAL_SSDP_INVENTORY] because what they imply differs — WS-Discovery inventories printers
+     * and cameras, while NetBIOS/LLMNR chatter is a security finding in its own right.
+     */
+    const val LOCAL_WSD_INVENTORY = "local.wsd_inventory"
+    const val LOCAL_NETBIOS_INVENTORY = "local.netbios_inventory"
     const val LOCAL_GATEWAY_SERVICES = "local.gateway_services"
     const val LOCAL_NTP = "local.ntp"
     // peer

echolot-app/core-measurement/src/main/kotlin/app/echo_lot/measurement/V6Analysis.kt

@@ -0,0 +1,73 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.measurement
+
+/**
+ * The two ways a network can be half-configured for IPv6, read from the link snapshot.
+ *
+ * Pure model logic rather than something a ViewModel does, because "is this network's IPv6
+ * broken, and in which direction" is exactly the kind of judgement that should be checkable
+ * against a captured routing table without a phone in the loop.
+ */
+object V6Analysis {
+
+    /** Linux tunnel interfaces: WireGuard/Netbird (tun*, wg*), plus the usual VPN names. */
+    private val TUNNEL_IFACE = Regex("""^(tun|tap|wg|ppp|ipsec|utun)\d*$""")
+
+    /** What one network's IPv6 configuration looks like. */
+    data class Shape(
+        val iface: String,
+        /** A global address with no ::/0 route: an address the device cannot route with. */
+        val addressWithoutRoute: Boolean,
+        /** A ::/0 route with no global address: a route the device cannot source from. */
+        val routeWithoutAddress: Boolean,
+        /** The routes belong to a tunnel, so a partial view of IPv6 is likely deliberate. */
+        val tunnel: Boolean,
+    )
+
+    /**
+     * Classifies each network's IPv6 configuration.
+     *
+     * Both shapes are read straight from the link snapshot rather than inferred from silence, so
+     * unlike an ICMP signal there is no competing explanation for what was observed — and both
+     * matter for the same reason: an application cannot tell in advance, so it tries IPv6 first
+     * and waits.
+     *
+     * They differ in what they mean. An address with no route is what a VPN installing host routes
+     * to specific destinations produces on purpose, and it works; calling that a fault would be the
+     * "lack of IPv6 is a yellow condition" mistake in a new costume, so a tunnel downgrades it to
+     * information. A route with no address is the opposite: the router advertised itself as a
+     * default gateway but SLAAC produced nothing usable, so the network is announcing IPv6 service
+     * it does not deliver. That one is a real misconfiguration however it arises.
+     */
+    fun classify(networks: List<Network>): List<Shape> = networks.map { n ->
+        val globalV6 = n.link.addresses.any { isGlobalV6(it.addr) }
+        val v6Routes = n.link.routes.filter { it.dst.contains(':') }
+        val hasDefault = v6Routes.any { it.dst == "::/0" }
+        Shape(
+            iface = n.iface ?: v6Routes.firstOrNull()?.iface.orEmpty(),
+            addressWithoutRoute = globalV6 && !hasDefault,
+            routeWithoutAddress = hasDefault && !globalV6,
+            // Android labels the transport itself, which beats guessing from a name; the regex
+            // stays as a backstop for tunnels Android does not own (a userspace WireGuard, say,
+            // or anything seen through the shell tier).
+            tunnel = n.transport == Transport.VPN ||
+                v6Routes.any { TUNNEL_IFACE.containsMatchIn(it.iface.orEmpty()) },
+        )
+    }
+
+    /**
+     * Whether an address is IPv6 and usable as a source for off-link traffic.
+     *
+     * ULAs count. A ULA is not globally routable, but it is a global-*scope* address the stack
+     * will happily select as a source, which is the property that matters here — an overlay
+     * network handing out fc00::/7 addresses is providing working IPv6 to the destinations it
+     * carries, and treating that as "no address" would misreport every VPN as broken.
+     */
+    private fun isGlobalV6(addr: String): Boolean {
+        if (!addr.contains(':')) return false
+        val a = addr.substringBefore('%').lowercase() // strip any zone index
+        return !a.startsWith("fe80") && a != "::1" && a != "::"
+    }
+}

echolot-app/core-measurement/src/test/kotlin/app/echo_lot/measurement/NetworkChangesTest.kt

@@ -0,0 +1,65 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.measurement
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/**
+ * Pins the counting behind `connectivity.link_flapping`.
+ *
+ * The finding claims a link went away and came back, and its severity escalates on repetition, so
+ * this is arithmetic a person reading a report will act on. The cases that matter are the ones
+ * where the naive count is wrong: a link still down when the window closed, and a run that started
+ * while the link was already gone.
+ */
+class NetworkChangesTest {
+
+    @Test
+    fun aQuietWindowHasNoCycles() {
+        assertEquals(0, NetworkChanges.flapCycles(emptyList()))
+        assertEquals(0, NetworkChanges.flapCycles(listOf("link_changed", "link_changed")))
+    }
+
+    @Test
+    fun oneDropAndReturnIsOneCycle() {
+        assertEquals(1, NetworkChanges.flapCycles(listOf("lost", "gained")))
+        assertEquals(
+            1,
+            NetworkChanges.flapCycles(listOf("link_changed", "lost", "link_changed", "gained")),
+        )
+    }
+
+    @Test
+    fun repeatedDropsCountSeparately() {
+        assertEquals(3, NetworkChanges.flapCycles(listOf("lost", "gained", "lost", "gained", "lost", "gained")))
+    }
+
+    // A link that is still down when the run ends was not flapping — it was switched off, or the
+    // device left its range. Counting that as a cycle would put a phone in a lift beside a failing
+    // access point.
+    @Test
+    fun aDropThatNeverReturnsIsNotACycle() {
+        assertEquals(0, NetworkChanges.flapCycles(listOf("lost")))
+        assertEquals(1, NetworkChanges.flapCycles(listOf("lost", "gained", "lost")))
+    }
+
+    // The mirror case: the window opened while the network was already gone, so its return is the
+    // first thing seen. Nothing was watched dropping, so nothing is claimed.
+    @Test
+    fun aReturnWithNoObservedDropIsNotACycle() {
+        assertEquals(0, NetworkChanges.flapCycles(listOf("gained")))
+        assertEquals(0, NetworkChanges.flapCycles(listOf("gained", "link_changed")))
+    }
+
+    @Test
+    fun theChangeOverloadAgreesWithTheKindsOverload() {
+        val changes = listOf(
+            NetworkChange(atMonoNs = 1, kind = NetworkChanges.LOST),
+            NetworkChange(atMonoNs = 2, kind = NetworkChanges.GAINED),
+            NetworkChange(atMonoNs = 3, kind = NetworkChanges.LINK_CHANGED),
+        )
+        assertEquals(1, NetworkChanges.flapCyclesOf(changes))
+    }
+}

echolot-app/core-measurement/src/test/kotlin/app/echo_lot/measurement/V6AnalysisTest.kt

@@ -0,0 +1,125 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.measurement
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+/**
+ * The fixtures here are a real device's routing table, transcribed from `dumpsys connectivity`
+ * on a OnePlus 15 with a Netbird tunnel up: wifi advertising a default route it cannot source
+ * from, cellular working properly, and a VPN carrying host routes to two destinations.
+ *
+ * Using a captured table rather than invented ones matters, because the bug this guards against
+ * is not "the boolean logic is wrong" — it is "the shapes I imagined are not the shapes real
+ * networks produce".
+ */
+class V6AnalysisTest {
+
+    private fun net(
+        id: String,
+        transport: Transport,
+        iface: String,
+        addrs: List<String>,
+        routes: List<Pair<String, String>>,
+    ) = Network(
+        id = id,
+        transport = transport,
+        iface = iface,
+        link = Link(
+            addresses = addrs.map { Address(addr = it.substringBefore('/'), prefixLen = 64) },
+            routes = routes.map { (dst, dev) -> Route(dst = dst, iface = dev) },
+        ),
+    )
+
+    /** wlan0: an IPv6 default route via a link-local gateway, but SLAAC produced no address. */
+    private val wifi = net(
+        "w", Transport.WIFI, "wlan0",
+        addrs = listOf("fe80::bcf6:edff:fe67:b139", "10.13.102.122"),
+        routes = listOf(
+            "fe80::/64" to "wlan0",
+            "::/0" to "wlan0",
+            "0.0.0.0/0" to "wlan0",
+        ),
+    )
+
+    /** rmnet_data1: a properly configured cellular link — global address and a default route. */
+    private val cellular = net(
+        "c", Transport.CELLULAR, "rmnet_data1",
+        addrs = listOf("2001:4bb8:46a:e724:289d:87ff:feb6:ebd3"),
+        routes = listOf("::/0" to "rmnet_data1", "2001:4bb8:46a:e724::/64" to "rmnet_data1"),
+    )
+
+    /** tun1: Netbird, with a ULA and host routes to exactly two destinations. */
+    private val vpn = net(
+        "v", Transport.VPN, "tun1",
+        addrs = listOf("100.64.158.131", "fdfd:c4fe:c4fe:c4fe:1f3c:98a0:dd66:ac7"),
+        routes = listOf(
+            "2001:1ad0:c4fe:6767::2/128" to "tun1",
+            "2001:1ad0:c4fe:a::136/128" to "tun1",
+            "fdfd:c4fe:c4fe:c4fe::/64" to "tun1",
+        ),
+    )
+
+    @Test
+    fun `wifi advertising a route it cannot source from is reported`() {
+        val s = V6Analysis.classify(listOf(wifi)).single()
+        assertTrue(s.routeWithoutAddress, "::/0 with only a link-local address is the RA-without-SLAAC case")
+        assertFalse(s.addressWithoutRoute)
+        assertFalse(s.tunnel, "wifi is not a tunnel")
+        assertEquals("wlan0", s.iface)
+    }
+
+    @Test
+    fun `a properly configured link produces no finding`() {
+        val s = V6Analysis.classify(listOf(cellular)).single()
+        assertFalse(s.routeWithoutAddress)
+        assertFalse(s.addressWithoutRoute)
+    }
+
+    @Test
+    fun `a tunnel with host routes is deliberate, not broken`() {
+        val s = V6Analysis.classify(listOf(vpn)).single()
+        assertTrue(s.addressWithoutRoute, "a ULA and no ::/0 is an address with nothing to route it")
+        assertTrue(s.tunnel, "so it must be reported as information, not as a fault")
+        assertFalse(s.routeWithoutAddress)
+    }
+
+    @Test
+    fun `each network is judged on its own`() {
+        // The whole point of per-network classification: "IPv6 is broken" is useless advice when
+        // wifi is the broken one and cellular is fine.
+        val shapes = V6Analysis.classify(listOf(wifi, cellular, vpn)).associateBy { it.iface }
+        assertTrue(shapes.getValue("wlan0").routeWithoutAddress)
+        assertFalse(shapes.getValue("rmnet_data1").routeWithoutAddress)
+        assertFalse(shapes.getValue("rmnet_data1").addressWithoutRoute)
+        assertTrue(shapes.getValue("tun1").addressWithoutRoute)
+    }
+
+    @Test
+    fun `a link-local-only network with no v6 route says nothing either way`() {
+        // Plain IPv4-only wifi: no IPv6 offered at all. That is v6.not_offered's business, and
+        // reporting it here as well would double up on a network that is merely legacy, not broken.
+        val v4only = net(
+            "4", Transport.WIFI, "wlan0",
+            addrs = listOf("fe80::1", "192.168.1.5"),
+            routes = listOf("0.0.0.0/0" to "wlan0"),
+        )
+        val s = V6Analysis.classify(listOf(v4only)).single()
+        assertFalse(s.routeWithoutAddress)
+        assertFalse(s.addressWithoutRoute)
+    }
+
+    @Test
+    fun `a zone index does not hide a link-local address`() {
+        val zoned = net(
+            "z", Transport.WIFI, "wlan0",
+            addrs = listOf("fe80::1%wlan0"),
+            routes = listOf("::/0" to "wlan0"),
+        )
+        assertTrue(V6Analysis.classify(listOf(zoned)).single().routeWithoutAddress)
+    }
+}

echolot-app/core-privacy/src/main/kotlin/app/echo_lot/privacy/Classification.kt

@@ -40,6 +40,10 @@ object Classification {
         listOf(
             "addr", "address", "gateway", "dst", "src", "servers", "server", "resolver",
             "next_hop", "via", "public_ip", "observed_ip",
+            // Who sent each passive-discovery announcement (SSDP / LLMNR / NetBIOS / WS-Discovery).
+            // Family-agnostic on purpose: the same field carries a dotted quad from a v4 group and
+            // a link-local from ff02::c, and the v6 transform hands dotted quads to the v4 path.
+            "source_ip",
         ).forEach { put(it, LogicalType.IP6) }
 
         listOf("mac", "hw_addr", "gateway_mac", "router_mac", "sender_mac", "peer_mac")
@@ -52,13 +56,28 @@ object Classification {
             "friendly_name", "server_name", "sni", "cname", "search_domain", "device_name",
             // Plural and prefixed variants the models actually use.
             "search_domains", "private_dns_hostname", "domains", "hostnames",
+            // Names a device shouts at the whole segment. An LLMNR question and a NetBIOS
+            // registration are hostnames in every sense that matters here — they name a machine on
+            // somebody's home network — so they get the same per-label treatment as any other.
+            "netbios_name",
         ).forEach { put(it, LogicalType.FQDN) }
 
-        listOf("session_id", "credential", "token", "device_id", "android_id", "serial", "imsi", "iccid")
-            .forEach { put(it, LogicalType.OPAQUE_ID) }
+        listOf(
+            "session_id", "credential", "token", "device_id", "android_id", "serial", "imsi", "iccid",
+            // Discovery identities. A UPnP USN and a WS-Discovery endpoint UUID are stable,
+            // globally unique per device and frequently derived from a serial number — exactly the
+            // thing that lets two uploads be recognised as the same household.
+            "usn", "device_uuid",
+        ).forEach { put(it, LogicalType.OPAQUE_ID) }
 
-        listOf("notes", "detail", "raw", "excerpt", "location", "model_description")
-            .forEach { put(it, LogicalType.FREETEXT) }
+        listOf(
+            "notes", "detail", "raw", "excerpt", "location", "model_description",
+            // The make/model a device volunteers, and the URLs it points at. `server_banner` is
+            // deliberately not named `server`, which the family-agnostic address block already
+            // claims — a SERVER header run through the address transform would be mangled into
+            // nonsense while protecting nothing.
+            "server_banner", "product_hint", "wsd_types", "wsd_xaddrs",
+        ).forEach { put(it, LogicalType.FREETEXT) }
     }
 
     /**
@@ -79,6 +98,13 @@ object Classification {
     private val droppedKeys = setOf(
         "ssdp_responders", "upnp", "neighbors", "arp_table", "scan_results",
         "nearby_networks", "peers", "raw_dump", "dumpsys",
+        // The long run's passive-discovery inventories. Same argument as `ssdp_responders`, only
+        // more so: these are minutes of everything the segment said about itself — device models,
+        // hostnames, printers, who is looking for whom. Even fully pseudonymized the *shape* of a
+        // household is a fingerprint, no metric depends on the list (the counts live in `metrics`,
+        // which survives), and the collectors' own status fields stay behind to say the capture
+        // worked. Dropping beats mangling.
+        "ssdp_devices", "llmnr_queries", "netbios_names", "wsd_devices",
     )
 
     fun typeOf(key: String, path: List<String>): LogicalType? {

echolot-app/core-probe/build.gradle.kts

@@ -28,4 +28,9 @@ dependencies {
     implementation(project(":core-measurement"))
     implementation(libs.kotlinx.serialization.json)
     implementation(libs.kotlinx.coroutines.android)
+    // JVM unit tests for the pure wire-format decoders (DiscoveryParsers.kt) against realistic and
+    // deliberately malformed payloads — no device, no Android runtime. Same setup as core-shizuku's
+    // dump-parser tests: JUnit 4, because that is what AGP's unit-test source set runs.
+    testImplementation(libs.kotlin.test.junit)
+    testImplementation(libs.junit4)
 }

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/Collector.kt

@@ -0,0 +1,78 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.Tier
+
+/**
+ * A measurement that watches, rather than one that asks — the long-run counterpart to [Probe].
+ *
+ * The difference is not duration but what is observable at all. A [Probe] describes the network
+ * during its own two seconds, so anything intermittent is invisible to the whole battery unless it
+ * happens to coincide with a probe: a wifi link that drops for four seconds every two minutes is
+ * reported as perfectly healthy by every one-shot test, both before and after the gap. A collector
+ * starts at t=0, keeps sampling while the battery runs beside it and after it finishes, and yields
+ * one [Test] when the window closes.
+ *
+ * Contract, and all of it is load-bearing for a run that can be cancelled at any second:
+ *  - [start] must return promptly, having launched whatever it needs on its own scope. The battery
+ *    runs concurrently and must not wait for a listener.
+ *  - [stop] must be callable after a failed [start], must never throw, and must return whatever was
+ *    gathered so far. A cancelled long run still owes the user the two minutes it did watch.
+ *  - Neither may throw to the caller; a collector that could not register its listener reports that
+ *    as an `unsupported` Test, which is a result rather than an absence.
+ */
+interface Collector {
+    /** A TestType registry id — collectors do not get their own namespace. */
+    val type: String
+    val tier: Tier get() = Tier.APP
+
+    suspend fun start(ctx: Context, ids: ProbeIds)
+
+    suspend fun stop(): Test
+}
+
+/**
+ * Shared plumbing: the ids and the [TestBuilder] a collector needs in [Collector.stop], captured in
+ * [Collector.start] before anything that can fail.
+ *
+ * Assigned first thing on purpose. A collector whose registration throws still has to produce a
+ * Test saying so, and it cannot do that without a UUID source and a start timestamp — so acquiring
+ * them is never allowed to be the step that failed.
+ */
+abstract class BaseCollector : Collector {
+
+    protected var ids: ProbeIds? = null
+        private set
+    private var builder: TestBuilder? = null
+
+    /** Call at the top of [Collector.start], before any platform call. */
+    protected fun begin(ids: ProbeIds, networkRef: String? = null) {
+        this.ids = ids
+        builder = TestBuilder(type, tier, ids, networkRef = networkRef)
+    }
+
+    /**
+     * Builds this collector's Test, or — when [begin] never ran, so the collector was stopped
+     * without ever being started — a `skipped` one saying exactly that. It reports rather than
+     * throws for the same reason probes do: the caller is assembling a document, and an exception
+     * there costs every other collector's data too.
+     */
+    protected fun build(
+        status: TestStatus,
+        evidence: kotlinx.serialization.json.JsonObject? = null,
+        metrics: kotlinx.serialization.json.JsonObject? = null,
+        error: TestError? = null,
+        params: kotlinx.serialization.json.JsonObject? = null,
+    ): Test = builder?.build(status, evidence, metrics, error, params)
+        ?: Test(
+            id = "00000000-0000-7000-8000-000000000000", type = type, tier = tier,
+            startedMonoNs = 0, endedMonoNs = 0, status = TestStatus.SKIPPED,
+            error = TestError("not_started", "the collector was stopped before it was started"),
+        )
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/ConstraintDetector.kt

@@ -0,0 +1,74 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import android.net.ConnectivityManager
+import android.net.NetworkCapabilities
+import android.system.ErrnoException
+import android.system.OsConstants
+import app.echo_lot.measurement.Constraints
+import app.echo_lot.measurement.Transport
+import java.net.DatagramSocket
+
+/**
+ * Detects what will prevent this run from measuring (measurement-schema.md §3 `constraints`),
+ * before any probe runs and independently of all of them.
+ *
+ * The known case: while a VPN holds the default route, Android refuses `Network.bindSocket()` on
+ * the underlying networks (EPERM) so apps cannot leak around the tunnel. Every per-network test
+ * then silently measures the tunnel or nothing, and the run comes out shaped exactly like a clean
+ * run of a healthy network. Detecting that here — one throwaway bind per network — is what lets
+ * the document say "these networks went unmeasured" instead of leaving the reader to infer it
+ * from a pattern of `attempted: false` scattered across the tests.
+ */
+object ConstraintDetector {
+
+    fun detect(ctx: Context, entries: List<NetworkInventory.Entry>): Constraints {
+        val cm = ctx.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
+        // "A VPN holds the default route" is judged from the ACTIVE network, not from a VPN
+        // network merely existing in the list: a tunnel that was just disconnected lingers in
+        // allNetworks while it tears down, and counting it kept the app claiming "measured
+        // through a VPN" after the VPN was gone.
+        val vpnActive = runCatching {
+            cm.getNetworkCapabilities(cm.activeNetwork)
+                ?.hasTransport(NetworkCapabilities.TRANSPORT_VPN) == true
+        }.getOrDefault(false)
+
+        val refused = ArrayList<String>()
+        for (e in entries) {
+            // The tunnel itself stays bindable — it is the underlying networks the OS walls off.
+            if (e.model.transport == Transport.VPN) continue
+            // Networks an app may never bind (carrier IMS/VoLTE, MMS, XCAP — no INTERNET, no
+            // NOT_RESTRICTED) refuse with EPERM permanently, VPN or no VPN. Counting them as a
+            // constraint is what made a phone with VoLTE report "measurement blocked" forever
+            // and forced every run INCONCLUSIVE. They are recorded in networks[] as
+            // app_usable:false; they are not something a run failed to do.
+            if (e.model.appUsable == false) continue
+            val err = try {
+                DatagramSocket().use { s -> e.handle.bindSocket(s) }
+                null
+            } catch (t: Throwable) {
+                t
+            }
+            // Only the OS *refusing* counts as blocked (EPERM: the VPN wall). A network that
+            // happens to die mid-snapshot fails its bind too, but with a different errno, and
+            // calling that "per-network probing blocked" would flip a whole healthy run to
+            // INCONCLUSIVE over one network going away — the probes already record
+            // attempted:false for that case.
+            if (err != null && isPermissionRefusal(err)) refused.add(e.model.id)
+        }
+        return Constraints(
+            vpnActive = vpnActive,
+            perNetworkBlocked = refused.isNotEmpty(),
+            unmeasuredNetworks = refused,
+        )
+    }
+
+    private fun isPermissionRefusal(t: Throwable): Boolean =
+        generateSequence(t) { it.cause }.any {
+            (it is ErrnoException && it.errno == OsConstants.EPERM) ||
+                (it.message?.contains("EPERM") == true)
+        }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/DiscoveryParsers.kt

@@ -0,0 +1,360 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+/**
+ * Wire-format decoders for the passive discovery collectors (SSDP, LLMNR, NetBIOS-NS, WS-Discovery).
+ *
+ * No Android imports on purpose: every byte these see was broadcast by an unidentified device on
+ * someone else's network, so they are the part of the collectors that most needs to be exercised
+ * against malformed input — and that is only cheap to do if it runs on a plain JVM. See
+ * DiscoveryParsersTest.
+ *
+ * The universal contract here is **return null, never throw**. A collector that dies on one
+ * malformed datagram loses the whole window's inventory, and a device that emits garbage is a
+ * device we still want counted. Every decoder therefore bounds-checks by hand rather than relying
+ * on an exception, and treats "this is not the protocol I parse" and "this is the protocol but it
+ * is broken" as the same answer: nothing to record.
+ */
+
+// ---- shared -------------------------------------------------------------------------------
+
+/**
+ * Makes a decoded string safe to embed in a JSON document.
+ *
+ * Names arrive as arbitrary bytes. Control characters would survive JSON encoding as escapes and
+ * turn up in a terminal that interprets them, and an unbounded length is a memory cost decided by
+ * whoever is shouting on the segment — so both are capped here rather than at each call site.
+ */
+internal fun sanitizeText(s: String, max: Int = 255): String {
+    val sb = StringBuilder(minOf(s.length, max))
+    for (c in s) {
+        if (sb.length >= max) break
+        sb.append(if (c.isISOControl() || c == '�') '?' else c)
+    }
+    return sb.toString()
+}
+
+private fun u8(b: ByteArray, i: Int) = b[i].toInt() and 0xFF
+private fun u16(b: ByteArray, i: Int) = (u8(b, i) shl 8) or u8(b, i + 1)
+
+// ---- SSDP ---------------------------------------------------------------------------------
+
+enum class SsdpKind { ALIVE, BYEBYE, UPDATE, RESPONSE, SEARCH, OTHER }
+
+/**
+ * One SSDP message. [target] is NT for announcements and ST for search responses — they name the
+ * same thing (which service is being talked about) from the two sides of the conversation, so they
+ * collapse into one field.
+ */
+data class SsdpMessage(
+    val kind: SsdpKind,
+    val target: String?,
+    val usn: String?,
+    val serverBanner: String?,
+    val location: String?,
+)
+
+object SsdpParser {
+
+    /**
+     * SSDP is HTTP-shaped but is not HTTP: there is no framing, no content length, and vendors
+     * disagree about line endings. Parsing it as "a start line plus colon-separated headers, be
+     * liberal about the rest" is the whole job — running it through an HTTP client would reject
+     * messages that real devices send and that we want to count.
+     *
+     * ISO-8859-1 decoding because the headers are byte-oriented and this mapping is total: no byte
+     * sequence can fail to decode, so a device with a Latin-1 model name in its SERVER banner is
+     * recorded rather than replaced by question marks.
+     */
+    fun parse(bytes: ByteArray, len: Int): SsdpMessage? {
+        if (len <= 0 || len > bytes.size) return null
+        val text = String(bytes, 0, len, Charsets.ISO_8859_1)
+        val lines = text.split('\n')
+        val start = lines.firstOrNull()?.trim().orEmpty()
+        if (start.isEmpty()) return null
+
+        val headers = HashMap<String, String>()
+        for (i in 1 until lines.size) {
+            val line = lines[i].trimEnd('\r')
+            if (line.isBlank()) break
+            val c = line.indexOf(':')
+            if (c <= 0) continue
+            val key = line.substring(0, c).trim().uppercase()
+            // First occurrence wins: a duplicated header is a device bug, and taking the first
+            // matches what every SSDP implementation in the wild does.
+            if (key !in headers) headers[key] = sanitizeText(line.substring(c + 1).trim(), 512)
+        }
+
+        val kind = when {
+            start.startsWith("NOTIFY", ignoreCase = true) -> when (headers["NTS"]?.lowercase()) {
+                "ssdp:alive" -> SsdpKind.ALIVE
+                "ssdp:byebye" -> SsdpKind.BYEBYE
+                "ssdp:update" -> SsdpKind.UPDATE
+                else -> SsdpKind.OTHER
+            }
+            start.startsWith("M-SEARCH", ignoreCase = true) -> SsdpKind.SEARCH
+            start.startsWith("HTTP/", ignoreCase = true) -> SsdpKind.RESPONSE
+            else -> return null // not SSDP at all
+        }
+
+        return SsdpMessage(
+            kind = kind,
+            target = headers["NT"] ?: headers["ST"],
+            usn = headers["USN"],
+            serverBanner = headers["SERVER"],
+            location = headers["LOCATION"],
+        )
+    }
+
+    /**
+     * The make/model inside a SERVER banner, as a hint.
+     *
+     * A banner reads `Linux/4.4 UPnP/1.0 Synology/DSM-7.3` or `FRITZ!Box 7590 UPnP/1.0`: the
+     * interesting token is whichever one is not the OS and not the protocol version, and there is
+     * no grammar that says which. Dropping the known-boilerplate tokens and keeping the rest is
+     * therefore a heuristic and is reported as such — [SsdpMessage.serverBanner] is kept verbatim
+     * beside it so nobody has to trust this to read the evidence.
+     */
+    fun productHint(serverBanner: String?): String? {
+        val banner = serverBanner?.trim().orEmpty()
+        if (banner.isEmpty()) return null
+        val kept = banner.split(' ', '\t')
+            .map { it.trim() }
+            .filter { it.isNotEmpty() && it.substringBefore('/').lowercase() !in BOILERPLATE }
+            .distinct()
+        return kept.joinToString(" ").takeIf { it.isNotEmpty() }
+    }
+
+    private val BOILERPLATE = setOf(
+        "upnp", "http", "dlnadoc", "linux", "unix", "windows", "darwin", "posix", "sdk",
+        "upnp-device-host", "microsoft-windows", "mono.upnp", "webos", "android",
+    )
+}
+
+// ---- DNS-format questions (LLMNR, and the shape NetBIOS-NS borrows) -------------------------
+
+/** One question from a DNS-format packet. [isQuery] separates "who is asking" from "who answered". */
+data class DnsQuestion(
+    val id: Int,
+    val name: String,
+    val qtype: Int,
+    val qclass: Int,
+    val isQuery: Boolean,
+    val opcode: Int,
+)
+
+object LlmnrParser {
+
+    /**
+     * Decodes the first question of an LLMNR packet, which is DNS wire format with a different
+     * transport.
+     *
+     * Name compression is rejected rather than followed. RFC 4795 forbids it in LLMNR, so a pointer
+     * here is either a broken sender or someone hoping the parser will chase it — and a pointer
+     * loop is the classic way to hang a DNS decoder. Refusing costs nothing real and removes the
+     * only unbounded loop this decoder could have had.
+     */
+    fun parse(bytes: ByteArray, len: Int): DnsQuestion? {
+        if (len < HEADER + 5 || len > bytes.size) return null
+        val flags = u16(bytes, 2)
+        if (u16(bytes, 4) < 1) return null // no question section
+
+        val sb = StringBuilder()
+        var i = HEADER
+        var labels = 0
+        while (true) {
+            if (i >= len) return null
+            val l = u8(bytes, i)
+            if (l == 0) { i++; break }
+            if (l and 0xC0 != 0) return null // compression pointer / reserved length
+            i++
+            if (i + l > len) return null
+            if (++labels > MAX_LABELS || sb.length + l > MAX_NAME) return null
+            if (sb.isNotEmpty()) sb.append('.')
+            sb.append(String(bytes, i, l, Charsets.UTF_8))
+            i += l
+        }
+        if (sb.isEmpty()) return null
+        if (i + 4 > len) return null
+
+        return DnsQuestion(
+            id = u16(bytes, 0),
+            name = sanitizeText(sb.toString()),
+            qtype = u16(bytes, i),
+            qclass = u16(bytes, i + 2),
+            isQuery = (flags and 0x8000) == 0,
+            opcode = (flags shr 11) and 0x0F,
+        )
+    }
+
+    /** The record types worth naming in evidence; anything else is reported as its number. */
+    fun qtypeName(qtype: Int): String = when (qtype) {
+        1 -> "A"
+        28 -> "AAAA"
+        12 -> "PTR"
+        33 -> "SRV"
+        255 -> "ANY"
+        else -> qtype.toString()
+    }
+
+    private const val HEADER = 12
+    private const val MAX_LABELS = 64
+    private const val MAX_NAME = 255
+}
+
+// ---- NetBIOS name service ------------------------------------------------------------------
+
+/**
+ * A decoded NetBIOS name-service question.
+ *
+ * [suffix] is the sixteenth byte of the name and is the part an engineer reads first: it says what
+ * the announcement is *for* (a workstation, a file server, a browser election) rather than who is
+ * making it.
+ */
+data class NetbiosName(
+    val name: String,
+    val suffix: Int,
+    val role: String,
+    val isResponse: Boolean,
+    val opcode: Int,
+)
+
+object NetbiosParser {
+
+    /**
+     * Decodes the question name from an NBNS packet (RFC 1002 §4.2).
+     *
+     * The header is DNS-shaped, but the name is not: NetBIOS first-level encoding splits each of
+     * the 16 name bytes into two nibbles and adds 'A' to each, so a 16-byte name is always exactly
+     * 32 characters drawn from A-P. That fixed shape is also the validity check — anything outside
+     * A-P means this is not an NBNS name, and it is cheaper and safer to reject the packet than to
+     * guess at what a half-decodable name was supposed to say.
+     */
+    fun parse(bytes: ByteArray, len: Int): NetbiosName? {
+        if (len < HEADER + 34 || len > bytes.size) return null
+        if (u16(bytes, 4) < 1) return null // no question section
+        if (u8(bytes, HEADER) != ENCODED_LEN) return null
+
+        val raw = ByteArray(16)
+        for (j in 0 until 16) {
+            val hi = u8(bytes, HEADER + 1 + j * 2) - 'A'.code
+            val lo = u8(bytes, HEADER + 2 + j * 2) - 'A'.code
+            if (hi !in 0..15 || lo !in 0..15) return null
+            raw[j] = ((hi shl 4) or lo).toByte()
+        }
+
+        // The first 15 bytes are the name, space-padded; the 16th is the suffix.
+        val padded = String(raw, 0, 15, Charsets.ISO_8859_1)
+        val name = sanitizeText(padded.trimEnd { it == ' ' || it.isISOControl() }, 15)
+        if (name.isEmpty()) return null
+        val suffix = raw[15].toInt() and 0xFF
+        val flags = u16(bytes, 2)
+        return NetbiosName(
+            name = name,
+            suffix = suffix,
+            role = roleOf(suffix),
+            isResponse = (flags and 0x8000) != 0,
+            opcode = (flags shr 11) and 0x0F,
+        )
+    }
+
+    /** RFC 1001 §15 / the Microsoft suffix assignments people actually see on a LAN. */
+    fun roleOf(suffix: Int): String = when (suffix) {
+        0x00 -> "workstation"
+        0x03 -> "messenger"
+        0x1B -> "domain_master_browser"
+        0x1C -> "domain_controllers"
+        0x1D -> "master_browser"
+        0x1E -> "browser_elections"
+        0x20 -> "file_server"
+        else -> "suffix_0x%02X".format(suffix)
+    }
+
+    /** NBNS opcodes: what the sender is doing, not just that it is talking. */
+    fun opcodeName(opcode: Int): String = when (opcode) {
+        0 -> "query"
+        5 -> "registration"
+        6 -> "release"
+        7 -> "wack"
+        8 -> "refresh"
+        else -> "opcode_$opcode"
+    }
+
+    private const val HEADER = 12
+    private const val ENCODED_LEN = 32
+}
+
+// ---- WS-Discovery --------------------------------------------------------------------------
+
+/** The four things a WS-Discovery datagram is worth reading for. */
+data class WsdMessage(
+    val action: String?,
+    val deviceUuid: String?,
+    val types: String?,
+    val xaddrs: String?,
+)
+
+object WsdParser {
+
+    /**
+     * Pulls four leaf values out of SOAP-over-UDP by targeted matching, deliberately **without an
+     * XML parser**.
+     *
+     * The input is unauthenticated, unsolicited, and written by whatever is on the segment. Handing
+     * that to a real XML parser buys namespace correctness and pays for it with the whole XML
+     * attack surface — entity expansion (a 700-byte datagram that allocates gigabytes), DTDs that
+     * fetch external resources, and nesting deep enough to exhaust the stack — all inside a probe
+     * whose contract is that it never throws. None of that surface is needed to read four leaf
+     * elements out of a message we are only ever going to count and quote.
+     *
+     * So: cap the text, then match `<[prefix:]Tag ...>value<` with a character class that cannot
+     * backtrack. The worst case is a value we fail to extract, which is recorded as an absence.
+     */
+    fun parse(bytes: ByteArray, len: Int): WsdMessage? {
+        if (len <= 0 || len > bytes.size) return null
+        val text = String(bytes, 0, minOf(len, MAX_TEXT), Charsets.UTF_8)
+        if (!text.contains("Envelope", ignoreCase = true)) return null
+
+        // The action tail is the message type — Hello, Bye, Probe, ProbeMatches, ResolveMatches.
+        val action = leaf(text, "Action")?.substringAfterLast('/')?.takeIf { it.isNotEmpty() }
+        // The device's stable identity is an EndpointReference/Address holding a urn:uuid. Other
+        // Address elements exist (wsa:To names the discovery group), so the uuid shape picks the
+        // right one rather than the first one.
+        val uuid = leaves(text, "Address").firstOrNull { it.contains("uuid:", ignoreCase = true) }
+        val msg = WsdMessage(
+            action = action?.let { sanitizeText(it, 64) },
+            deviceUuid = uuid?.let { sanitizeText(it, 128) },
+            types = leaf(text, "Types")?.let { sanitizeText(it, 200) },
+            xaddrs = leaf(text, "XAddrs")?.let { sanitizeText(it, 300) },
+        )
+        val empty = msg.action == null && msg.deviceUuid == null &&
+            msg.types == null && msg.xaddrs == null
+        return if (empty) null else msg
+    }
+
+    private fun leaf(xml: String, tag: String): String? = leaves(xml, tag).firstOrNull()
+
+    private fun leaves(xml: String, tag: String): List<String> {
+        val re = TAGS[tag] ?: return emptyList()
+        return re.findAll(xml).map { it.groupValues[1].trim() }.filter { it.isNotEmpty() }.toList()
+    }
+
+    /**
+     * `[^<]{0,512}` rather than a lazy `.*?`: it can only ever match forward, so there is no input
+     * that makes this regex expensive. WS-Discovery leaves hold no markup, so nothing is lost.
+     *
+     * Built once, eagerly, because the alternative is a memoizing map touched from the capture
+     * thread — a data race for the sake of four Regex allocations.
+     */
+    private val TAGS: Map<String, Regex> =
+        listOf("Action", "Address", "Types", "XAddrs").associateWith { tag ->
+            Regex(
+                """<(?:[A-Za-z0-9_.\-]{1,32}:)?$tag\b[^>]{0,256}>([^<]{0,512})<""",
+                RegexOption.IGNORE_CASE,
+            )
+        }
+
+    private const val MAX_TEXT = 16 * 1024
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/DnsResolverProbe.kt

@@ -0,0 +1,227 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import java.net.DatagramPacket
+import java.net.DatagramSocket
+import java.net.InetAddress
+import java.net.InetSocketAddress
+import java.util.Random
+
+/**
+ * Asks the network's own DNS servers directly, then asks Android to resolve the same name, and
+ * compares.
+ *
+ * The comparison is the point. A name that fails to resolve looks the same to a user whatever the
+ * cause, but the causes want opposite responses: if the server does not answer, the network is
+ * broken and the router is the thing to look at; if the server answers a raw query while the
+ * platform still cannot resolve, the device's own resolver has wedged and toggling wifi fixes it in
+ * seconds. Nothing else on a phone will tell you which of those you have.
+ *
+ * This is deliberately not a general DNS test — no recursion checks, no DNSSEC, no rewriting
+ * detection; [DnsCanaryProbe] covers interception. This one answers a single question: is the
+ * resolver on this device doing its job.
+ */
+class DnsResolverProbe(
+    private val entries: List<NetworkInventory.Entry>,
+    /** Resolved directly rather than through any cache; any name with a stable answer will do. */
+    private val probeName: String = "one.one.one.one",
+) : Probe {
+    override val type = TestType.DNS_RESOLVER
+    override val tier = Tier.APP
+    // A query per server with a 3s ceiling, plus one getaddrinfo that may sit out its own timeout.
+    override val estimatedMs = 6_000L
+
+    override suspend fun run(ctx: Context, ids: ProbeIds): Test = withContext(Dispatchers.IO) {
+        val b = TestBuilder(type, tier, ids)
+        val perNetwork = LinkedHashMap<String, Pair<String, JsonObject>>()
+
+        for (e in entries) {
+            val servers = e.model.link.dns?.servers.orEmpty()
+            if (servers.isEmpty()) continue
+            val label = "${e.model.transport.name.lowercase()}:${e.model.id}"
+
+            // Directly: does the configured server answer at all?
+            var direct: Boolean? = null
+            var directDetail = "no server answered"
+            for (s in servers) {
+                val r = try {
+                    queryDirect(s, probeName)
+                } catch (e: DnsRefused) {
+                    // Distinguished deliberately: a server that replies with a failure is a
+                    // working server saying no, which points at the network rather than here.
+                    direct = false
+                    directDetail = "$s ${e.why}"
+                    break
+                }
+                if (r != null) {
+                    direct = true
+                    directDetail = "$s answered in ${r}ms"
+                    break
+                }
+                direct = false
+                directDetail = "$s did not answer"
+            }
+
+            // The search domains the network handed out, asked about separately.
+            //
+            // A resolver appends these to a lookup, so a search domain the server will not answer
+            // for stalls every name a client asks about — and it fails as silence, which is
+            // indistinguishable from packet loss, so clients retry rather than moving on. Asking
+            // about a name that cannot exist is deliberate: the answer wanted here is NXDOMAIN,
+            // and what matters is only whether anything comes back at all.
+            val searchDomains = e.model.link.dns?.searchDomains.orEmpty()
+            var searchAnswered: Boolean? = null
+            var searchDetail = ""
+            for (d in searchDomains) {
+                val nonce = "echolot-probe-" + java.util.UUID.randomUUID().toString().take(8)
+                val answered = servers.any { srv ->
+                    runCatching { queryDirect(srv, "$nonce.$d") != null }
+                        .getOrElse { it is DnsRefused } // a refusal is still an answer
+                }
+                if (!answered) {
+                    searchAnswered = false
+                    searchDetail = "$d is not answered at all — queries under it vanish"
+                    break
+                }
+                searchAnswered = true
+                searchDetail = "$d answers"
+            }
+
+            // Through the platform: what an app actually gets.
+            val viaSystem = runCatching {
+                e.handle.getAllByName(probeName).isNotEmpty()
+            }.getOrElse { false }
+
+            perNetwork[label] = e.model.id to buildJsonObject {
+                put("network_ref", e.model.id)
+                put("servers", servers.joinToString(","))
+                direct?.let { put("direct_answer", it) }
+                put("direct_detail", directDetail)
+                if (searchDomains.isNotEmpty()) {
+                    put("search_domains", searchDomains.joinToString(","))
+                    searchAnswered?.let { put("search_answered", it) }
+                    put("search_detail", searchDetail)
+                }
+                put("system_resolves", viaSystem)
+                // Named here rather than left for a finding to infer, because the pairing is the
+                // whole observation and splitting it across two places invites reading one alone.
+                put(
+                    "verdict",
+                    when {
+                        // Ordered by which component is at fault, most specific first. A search
+                        // domain that swallows queries explains a failure that would otherwise be
+                        // blamed on the device, so it has to be tested before that conclusion.
+                        searchAnswered == false -> "search domain swallows queries"
+                        viaSystem -> "resolver working"
+                        direct == true -> "server answers, device resolver does not"
+                        direct == false -> "server does not answer"
+                        else -> "not determined"
+                    },
+                )
+            }
+        }
+
+        if (perNetwork.isEmpty()) {
+            return@withContext b.build(
+                TestStatus.SKIPPED,
+                evidence = buildJsonObject { put("reason", "no network advertised a DNS server") },
+            )
+        }
+        val evidence = buildJsonObject {
+            put("name", probeName)
+            for ((label, v) in perNetwork) put(label, v.second)
+        }
+        // OK means the measurement ran, not that DNS is healthy — the finding says that.
+        b.build(TestStatus.OK, evidence = evidence)
+    }
+
+    /**
+     * Sends one A query straight to [server] over UDP. Returns the round trip in ms, or null.
+     *
+     * Hand-rolled rather than via any resolver API on purpose: the entire point is to bypass the
+     * component under suspicion. Anything that goes through the platform resolver would inherit
+     * exactly the fault this is trying to detect.
+     */
+    private fun queryDirect(server: String, name: String): Long? {
+        return try {
+            queryDirectOrThrow(server, name)
+        } catch (e: DnsRefused) {
+            throw e
+        } catch (t: Throwable) {
+            null
+        }
+    }
+
+    private fun queryDirectOrThrow(server: String, name: String): Long? = run {
+        val id = Random().nextInt(0xFFFF)
+        val query = buildQuery(id, name)
+        DatagramSocket().use { sock ->
+            sock.soTimeout = 3000
+            val addr = InetAddress.getByName(server) // a literal from DHCP; no lookup happens
+            val t0 = System.nanoTime()
+            sock.send(DatagramPacket(query, query.size, InetSocketAddress(addr, 53)))
+            val buf = ByteArray(512)
+            val reply = DatagramPacket(buf, buf.size)
+            sock.receive(reply)
+            val ms = (System.nanoTime() - t0) / 1_000_000
+            // A reply is not an answer. Counting any packet as success would let a REFUSED or
+            // SERVFAIL — both perfectly well-formed responses — be reported as "the server
+            // answers", and this probe's whole output is the claim that the server is fine and
+            // the device is not. That would be an accusation pointed at the wrong component,
+            // stated with confidence.
+            val replyId = ((buf[0].toInt() and 0xFF) shl 8) or (buf[1].toInt() and 0xFF)
+            val rcode = if (reply.length >= 4) buf[3].toInt() and 0x0F else -1
+            val answers = if (reply.length >= 8) {
+                ((buf[6].toInt() and 0xFF) shl 8) or (buf[7].toInt() and 0xFF)
+            } else 0
+            when {
+                replyId != id || reply.length < 12 -> null
+                rcode != 0 -> throw DnsRefused(rcodeName(rcode))
+                answers == 0 -> throw DnsRefused("answered with no records")
+                else -> ms
+            }
+        }
+    }
+
+    /** The server replied, but with a failure — which is a network fault, not a device one. */
+    private class DnsRefused(val why: String) : Exception(why)
+
+    private fun rcodeName(rcode: Int): String = when (rcode) {
+        1 -> "rejected the query as malformed"
+        2 -> "reported its own failure (SERVFAIL)"
+        3 -> "said the name does not exist (NXDOMAIN)"
+        4 -> "does not implement this query"
+        5 -> "refused the query (REFUSED)"
+        else -> "returned rcode $rcode"
+    }
+
+    /** A minimal DNS query: one question, class IN, type A, recursion desired. */
+    private fun buildQuery(id: Int, name: String): ByteArray {
+        val labels = name.split('.').filter { it.isNotEmpty() }
+        val out = ArrayList<Byte>(32)
+        out.add((id shr 8).toByte()); out.add(id.toByte())
+        out.add(0x01); out.add(0x00)   // recursion desired
+        out.add(0x00); out.add(0x01)   // one question
+        repeat(6) { out.add(0x00) }    // no answers, authority or additional
+        for (l in labels) {
+            out.add(l.length.toByte())
+            for (c in l.toByteArray(Charsets.US_ASCII)) out.add(c)
+        }
+        out.add(0x00)                  // root label
+        out.add(0x00); out.add(0x01)   // type A
+        out.add(0x00); out.add(0x01)   // class IN
+        return out.toByteArray()
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/IcmpEcho.kt

@@ -0,0 +1,113 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.net.Network
+import android.system.Os
+import android.system.OsConstants
+import android.system.StructTimeval
+import java.io.FileDescriptor
+import java.net.InetAddress
+import java.nio.ByteBuffer
+import java.util.Locale
+
+/**
+ * One echo exchange over the unprivileged ICMP datagram socket.
+ *
+ * Extracted from [IcmpProbe] when the long-run [PingSeriesCollector] needed the same exchange a
+ * few hundred times instead of once. The two differ only in how often they call this; a second
+ * copy of the checksum and the sent/not-sent bookkeeping would only be a second place for them to
+ * drift apart.
+ *
+ * Works without root because Android ships an open `ping_group_range` — validated on hardware by
+ * the prober, and the reason this probe family exists at app tier at all.
+ */
+internal object IcmpEcho {
+
+    /**
+     * One attempt's result.
+     *
+     * [attempted] separates "we sent an echo request and heard nothing" from "we never got as far
+     * as sending one". Both leave [ok] false, and collapsing them is how a probe ends up asserting
+     * something about a network it never touched: binding to a non-default network can fail with
+     * EPERM, and reporting that as ICMP silence blames the network for the app's own inability to
+     * use the interface. For a series it is also the difference between a lost packet and a socket
+     * that was never usable — one is loss, the other is not.
+     */
+    data class Result(
+        val ok: Boolean,
+        val attempted: Boolean,
+        val detail: String,
+        val rttMs: Double?,
+    )
+
+    fun ping(
+        network: Network?,
+        target: String,
+        v6: Boolean,
+        timeoutMs: Int,
+        seq: Int = 1,
+    ): Result {
+        var fd: FileDescriptor? = null
+        var sent = false
+        return try {
+            val proto = if (v6) OsConstants.IPPROTO_ICMPV6 else OsConstants.IPPROTO_ICMP
+            val family = if (v6) OsConstants.AF_INET6 else OsConstants.AF_INET
+            fd = Os.socket(family, OsConstants.SOCK_DGRAM, proto)
+            // Everything up to and including sendto is setup. A failure here means the test did
+            // not run on this network — not that the network stayed silent.
+            network?.bindSocket(fd)
+            Os.setsockoptTimeval(
+                fd, OsConstants.SOL_SOCKET, OsConstants.SO_RCVTIMEO,
+                StructTimeval.fromMillis(timeoutMs.toLong()),
+            )
+            val addr = network?.getByName(target) ?: InetAddress.getByName(target)
+
+            val ident = (Os.getpid() and 0xFFFF)
+            val packet = buildEchoRequest(v6, ident.toShort(), seq.toShort())
+            val t0 = System.nanoTime()
+            Os.sendto(fd, packet, 0, packet.size, 0, addr, 0)
+            sent = true
+            val buf = ByteBuffer.allocate(1500)
+            val received = Os.recvfrom(fd, buf, 0, null)
+            val rttMs = (System.nanoTime() - t0) / 1_000_000.0
+            val replyType = if (received > 0) buf.get(0).toInt() and 0xFF else -1
+            val ok = replyType == (if (v6) 129 else 0)
+            Result(
+                ok, true,
+                "reply type=$replyType rtt_ms=${"%.1f".format(Locale.ROOT, rttMs)} bytes=$received",
+                if (ok) rttMs else null,
+            )
+        } catch (e: Throwable) {
+            // A timeout after a successful send is a real "no reply"; anything before it is not.
+            Result(false, sent, "error: ${e.message ?: e.javaClass.simpleName}", null)
+        } finally {
+            fd?.let { runCatching { Os.close(it) } }
+        }
+    }
+
+    private fun buildEchoRequest(v6: Boolean, ident: Short, seq: Short): ByteArray {
+        val type = if (v6) 128 else 8
+        val payload = "echolot".toByteArray()
+        val pkt = ByteBuffer.allocate(8 + payload.size)
+        pkt.put(type.toByte()); pkt.put(0); pkt.putShort(0)
+        pkt.putShort(ident); pkt.putShort(seq); pkt.put(payload)
+        val bytes = pkt.array()
+        // The v6 checksum is computed by the kernel over a pseudo-header the socket owns; filling
+        // it in here would be wrong, not merely redundant.
+        if (!v6) {
+            val cs = checksum(bytes)
+            bytes[2] = (cs.toInt() shr 8).toByte(); bytes[3] = (cs.toInt() and 0xFF).toByte()
+        }
+        return bytes
+    }
+
+    private fun checksum(b: ByteArray): Short {
+        var sum = 0; var i = 0
+        while (i < b.size - 1) { sum += ((b[i].toInt() and 0xFF) shl 8) or (b[i + 1].toInt() and 0xFF); i += 2 }
+        if (i < b.size) sum += (b[i].toInt() and 0xFF) shl 8
+        while (sum shr 16 != 0) sum = (sum and 0xFFFF) + (sum shr 16)
+        return sum.inv().toShort()
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/IcmpProbe.kt

@@ -5,9 +5,6 @@ package app.echo_lot.probe
 
 import android.content.Context
 import android.net.Network
-import android.system.Os
-import android.system.OsConstants
-import android.system.StructTimeval
 import app.echo_lot.measurement.Test
 import app.echo_lot.measurement.TestStatus
 import app.echo_lot.measurement.TestType
@@ -17,10 +14,6 @@ import kotlinx.coroutines.withContext
 import kotlinx.serialization.json.JsonObject
 import kotlinx.serialization.json.buildJsonObject
 import kotlinx.serialization.json.put
-import java.io.FileDescriptor
-import java.net.InetAddress
-import java.nio.ByteBuffer
-import java.util.Locale
 
 /**
  * icmp.ping4 / icmp.ping6 via the unprivileged ICMP datagram socket, per active network
@@ -40,24 +33,37 @@ class IcmpProbe(
 
     override suspend fun run(ctx: Context, ids: ProbeIds): Test = withContext(Dispatchers.IO) {
         val b = TestBuilder(type, tier, ids)
-        val perNetwork = LinkedHashMap<String, String>()
+        val perNetwork = LinkedHashMap<String, Pair<String?, IcmpEcho.Result>>()
         var anyOk = false
         val rtts = ArrayList<Double>()
 
         // Default network first, then each active network explicitly.
-        attempt(null).let { (ok, detail, rtt) ->
-            perNetwork["default"] = detail; if (ok) { anyOk = true; rtt?.let(rtts::add) }
+        attempt(null).let { a ->
+            perNetwork["default"] = null to a
+            if (a.ok) { anyOk = true; a.rttMs?.let(rtts::add) }
         }
         for (e in entries) {
             val label = "${e.model.transport.name.lowercase()}:${e.model.id}"
-            val (ok, detail, rtt) = attempt(e.handle)
-            perNetwork[label] = detail
-            if (ok) { anyOk = true; rtt?.let(rtts::add) }
+            val a = attempt(e.handle)
+            perNetwork[label] = e.model.id to a
+            if (a.ok) { anyOk = true; a.rttMs?.let(rtts::add) }
         }
 
+        // Per-network results are recorded structurally, not just as prose. The aggregate status
+        // can only say "some network answered"; a finding needs to know *which* network failed,
+        // and recovering that by parsing a human-readable detail string would be a trap waiting to
+        // spring the first time the wording changes.
         val evidence: JsonObject = buildJsonObject {
             put("target", target)
-            for ((k, v) in perNetwork) put(k, v)
+            for ((label, r) in perNetwork) {
+                val (netId, a) = r
+                put(label, buildJsonObject {
+                    netId?.let { put("network_ref", it) }
+                    put("ok", a.ok)
+                    put("attempted", a.attempted)
+                    put("detail", a.detail)
+                })
+            }
         }
         val metrics: JsonObject = buildJsonObject {
             put("networks_ok", rtts.size)
@@ -69,56 +75,9 @@ class IcmpProbe(
         b.build(status, evidence = evidence, metrics = metrics)
     }
 
-    private data class Attempt(val ok: Boolean, val detail: String, val rttMs: Double?)
-
-    private fun attempt(network: Network?): Attempt {
-        var fd: FileDescriptor? = null
-        return try {
-            val proto = if (v6) OsConstants.IPPROTO_ICMPV6 else OsConstants.IPPROTO_ICMP
-            val family = if (v6) OsConstants.AF_INET6 else OsConstants.AF_INET
-            fd = Os.socket(family, OsConstants.SOCK_DGRAM, proto)
-            network?.bindSocket(fd)
-            Os.setsockoptTimeval(fd, OsConstants.SOL_SOCKET, OsConstants.SO_RCVTIMEO, StructTimeval.fromMillis(3000))
-            val addr = network?.getByName(target) ?: InetAddress.getByName(target)
-
-            val ident = (Os.getpid() and 0xFFFF)
-            val packet = buildEchoRequest(v6, ident.toShort(), 1)
-            val t0 = System.nanoTime()
-            Os.sendto(fd, packet, 0, packet.size, 0, addr, 0)
-            val buf = ByteBuffer.allocate(1500)
-            val received = Os.recvfrom(fd, buf, 0, null)
-            val rttMs = (System.nanoTime() - t0) / 1_000_000.0
-            val replyType = if (received > 0) buf.get(0).toInt() and 0xFF else -1
-            val ok = replyType == (if (v6) 129 else 0)
-            Attempt(ok, "reply type=$replyType rtt_ms=${"%.1f".format(Locale.ROOT, rttMs)} bytes=$received", if (ok) rttMs else null)
-        } catch (e: Throwable) {
-            Attempt(false, "error: ${e.message ?: e.javaClass.simpleName}", null)
-        } finally {
-            fd?.let { runCatching { Os.close(it) } }
-        }
-    }
-
-    private fun buildEchoRequest(v6: Boolean, ident: Short, seq: Short): ByteArray {
-        val type = if (v6) 128 else 8
-        val payload = "echolot".toByteArray()
-        val pkt = ByteBuffer.allocate(8 + payload.size)
-        pkt.put(type.toByte()); pkt.put(0); pkt.putShort(0)
-        pkt.putShort(ident); pkt.putShort(seq); pkt.put(payload)
-        val bytes = pkt.array()
-        if (!v6) {
-            val cs = checksum(bytes)
-            bytes[2] = (cs.toInt() shr 8).toByte(); bytes[3] = (cs.toInt() and 0xFF).toByte()
-        }
-        return bytes
-    }
-
-    private fun checksum(b: ByteArray): Short {
-        var sum = 0; var i = 0
-        while (i < b.size - 1) { sum += ((b[i].toInt() and 0xFF) shl 8) or (b[i + 1].toInt() and 0xFF); i += 2 }
-        if (i < b.size) sum += (b[i].toInt() and 0xFF) shl 8
-        while (sum shr 16 != 0) sum = (sum and 0xFFFF) + (sum shr 16)
-        return sum.inv().toShort()
-    }
+    /** The echo exchange itself lives in [IcmpEcho], shared with the long-run ping series. */
+    private fun attempt(network: Network?): IcmpEcho.Result =
+        IcmpEcho.ping(network, target, v6, timeoutMs = 3000)
 
     private companion object {
         fun round1(v: Double) = Math.round(v * 10.0) / 10.0

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/LlmnrCollector.kt

@@ -0,0 +1,124 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+
+/**
+ * local.llmnr_inventory — who is resolving names with LLMNR on this segment, and what for.
+ *
+ * The measurement is twofold, and the second half is the one people underestimate:
+ *
+ *  1. **Which hostnames are being looked up.** An LLMNR query is a device saying out loud, to
+ *     everyone, the name of something it wants to reach. Over a window that is a map of who talks
+ *     to whom — and, when the names are things like `wpad` or a server that no longer exists, a map
+ *     of what is failing to resolve through DNS and falling back.
+ *  2. **That LLMNR is in use at all.** LLMNR (and its NetBIOS sibling) is a name-resolution
+ *     fallback that trusts whoever answers first, which is the mechanism behind the standard
+ *     credential-relay attack on Windows networks. Its mere presence on a segment is a finding
+ *     independent of any individual query — which is why this earns a test id rather than folding
+ *     into the mDNS inventory.
+ *
+ * Purely passive: queries are broadcast to the group, so listening is the entire measurement, and
+ * answering or querying would make this device a participant in exactly the trust relationship the
+ * measurement is about.
+ */
+class LlmnrCollector : BaseCollector() {
+
+    override val type = TestType.LOCAL_LLMNR_INVENTORY
+    override val tier = Tier.APP
+
+    private val capture = MulticastCapture(
+        label = "llmnr",
+        port = PORT,
+        group4 = GROUP4,
+        // ff02::1:3 is the IPv6 LLMNR group. Joined where IPv6 exists; a v4-only network simply
+        // records an empty joined_v6 rather than an error, because that is not one.
+        group6 = GROUP6,
+    )
+
+    private var startedAtMonoNs = 0L
+
+    override suspend fun start(ctx: Context, ids: ProbeIds) {
+        begin(ids)
+        startedAtMonoNs = ids.monoNs()
+        capture.acquireLock(ctx)
+        capture.start(ids)
+    }
+
+    override suspend fun stop(): Test {
+        val packets = capture.stop()
+
+        val table = DiscoveryTable()
+        var queries = 0
+        var responses = 0
+        var undecodable = 0
+
+        for (p in packets) {
+            val q = LlmnrParser.parse(p.data, p.data.size)
+            if (q == null) {
+                undecodable++
+                continue
+            }
+            if (q.isQuery) queries++ else responses++
+            // Responses are normally unicast back to the querier, so what lands here is
+            // overwhelmingly queries — but a response that does reach the group is still a device
+            // claiming a name, which is worth the same row.
+            table.observe(p.sourceIp, "${q.name}/${q.qtype}", p.atMonoNs) {
+                buildJsonObject {
+                    put("query_name", q.name)
+                    put("qtype", LlmnrParser.qtypeName(q.qtype))
+                    put("kind", if (q.isQuery) "query" else "response")
+                }
+            }
+        }
+
+        val evidence: JsonObject = buildJsonObject {
+            put("capture", capture.statusJson())
+            put("llmnr_queries", table.toJson())
+            put("evidence_truncated", capture.truncated || table.overflowed)
+        }
+        val metrics: JsonObject = buildJsonObject {
+            put("distinct_sources", table.distinctSources)
+            put("distinct_names", table.size)
+            put("packets", capture.packetsSeen)
+            put("queries", queries)
+            put("responses", responses)
+            put("undecodable_packets", undecodable)
+            // The headline: whether this protocol is live here at all. A boolean rather than an
+            // inference from a count, so a reader (or a future finding rule) never has to decide
+            // what "zero packets" meant — the capture's own status says whether zero is trustworthy.
+            put("llmnr_in_use", table.distinctSources > 0)
+            put("truncated", capture.truncated || table.overflowed)
+        }
+        val saw = !table.isEmpty
+        return build(
+            capture.outcome(saw),
+            evidence = evidence,
+            metrics = metrics,
+            params = params(),
+            error = capture.reason(saw)?.let { TestError("listen_incomplete", it) },
+        )
+    }
+
+    private fun params(): JsonObject = buildJsonObject {
+        put("mode", "passive")
+        put("group_v4", "$GROUP4:$PORT")
+        put("group_v6", "[$GROUP6]:$PORT")
+        put("started_mono_ns", startedAtMonoNs)
+    }
+
+    private companion object {
+        const val PORT = 5355
+        const val GROUP4 = "224.0.0.252"
+        const val GROUP6 = "ff02::1:3"
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/MdnsInventoryProbe.kt

@@ -0,0 +1,115 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import android.net.nsd.NsdManager
+import android.net.nsd.NsdServiceInfo
+import android.net.wifi.WifiManager
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import kotlinx.serialization.json.putJsonObject
+import java.util.Collections
+
+/**
+ * local.mdns_inventory — what answers mDNS on this network (MulticastLock + NSD discovery).
+ * The service inventory doubles as the VLAN-leakage detector: a chromecast answering on the
+ * guest wifi is a segmentation fault made visible. Folded from the prober, validated on both
+ * known devices (4 services each).
+ *
+ * Two hardware-bought lessons are load-bearing here:
+ *  - The `_services._dns-sd._udp.` meta-query returned 0 on BOTH devices while concrete types
+ *    found live services — NsdManager's meta-query support is unreliable across builds, so the
+ *    concrete types are the measurement and the meta-query result is itself evidence.
+ *  - 4 s of listening missed services that 10 s catches; mDNS answers straggle.
+ *
+ * That last lesson is why [listenMs] is a parameter. 10 s is the short-mode default because it is
+ * the shortest window that was not demonstrably lossy; a long run hands it the whole measurement
+ * window, since the curve does not stop at ten seconds — devices announce on their own schedule,
+ * and a printer that is asleep answers when something else wakes it.
+ */
+class MdnsInventoryProbe(private val listenMs: Long = 10_000) : Probe {
+    override val type = TestType.LOCAL_MDNS_INVENTORY
+    override val tier = Tier.APP
+    override val estimatedMs = listenMs + 500
+
+    /** Meta-query + common concrete types (HTTP covers HA/printers/NAS; googlecast is ubiquitous). */
+    private val queries = listOf(
+        "meta" to "_services._dns-sd._udp.",
+        "http" to "_http._tcp.",
+        "googlecast" to "_googlecast._tcp.",
+    )
+
+    private class Recorder : NsdManager.DiscoveryListener {
+        val names: MutableList<String> = Collections.synchronizedList(mutableListOf())
+        @Volatile var started = false
+        @Volatile var startFailCode: Int? = null
+        override fun onStartDiscoveryFailed(t: String?, code: Int) { startFailCode = code }
+        override fun onStopDiscoveryFailed(t: String?, code: Int) {}
+        override fun onDiscoveryStarted(t: String?) { started = true }
+        override fun onDiscoveryStopped(t: String?) {}
+        override fun onServiceFound(s: NsdServiceInfo?) { s?.serviceName?.let { names.add(it) } }
+        override fun onServiceLost(s: NsdServiceInfo?) {}
+    }
+
+    override suspend fun run(ctx: Context, ids: ProbeIds): Test = withContext(Dispatchers.IO) {
+        val b = TestBuilder(type, tier, ids)
+        val wifi = ctx.getSystemService(WifiManager::class.java)
+        val lock = wifi?.createMulticastLock("echolot")?.apply {
+            setReferenceCounted(false)
+            runCatching { acquire() }
+        }
+        val nsd = ctx.getSystemService(NsdManager::class.java)
+            ?: return@withContext b.build(
+                TestStatus.UNSUPPORTED,
+                evidence = buildJsonObject { put("reason", "NsdManager unavailable") },
+            )
+
+        val recorders = queries.map { (label, type) ->
+            val r = Recorder()
+            runCatching { nsd.discoverServices(type, NsdManager.PROTOCOL_DNS_SD, r) }
+                .onFailure { r.startFailCode = -1 }
+            Triple(label, type, r)
+        }
+        try {
+            delay(listenMs)
+            var total = 0
+            var anyStarted = false
+            val evidence = buildJsonObject {
+                put("multicast_lock", lock?.isHeld == true)
+                for ((label, type, r) in recorders) {
+                    runCatching { nsd.stopServiceDiscovery(r) }
+                    anyStarted = anyStarted || r.started
+                    val names = r.names.distinct()
+                    total += names.size
+                    putJsonObject(label) {
+                        put("query", type)
+                        put("started", r.started)
+                        r.startFailCode?.let { put("start_fail_code", it) }
+                        put("found", names.size)
+                        if (names.isNotEmpty()) put("names", names.joinToString(", ").take(300))
+                    }
+                }
+            }
+            val metrics = buildJsonObject { put("services_found", total) }
+            // How long it listened belongs in params: "4 services" means something different after
+            // ten seconds than after five minutes, and the number alone cannot say which it was.
+            val params = buildJsonObject { put("listen_ms", listenMs) }
+            // Zero services on a started discovery is a legitimate result (an empty or properly
+            // isolated network), not a failure — only discovery refusing to start is one.
+            b.build(if (anyStarted) TestStatus.OK else TestStatus.FAILED,
+                evidence = evidence, metrics = metrics, params = params)
+        } finally {
+            recorders.forEach { (_, _, r) -> runCatching { nsd.stopServiceDiscovery(r) } }
+            runCatching { lock?.release() }
+        }
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/MulticastCapture.kt

@@ -0,0 +1,420 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import android.net.wifi.WifiManager
+import app.echo_lot.measurement.TestStatus
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import kotlinx.serialization.json.putJsonArray
+import kotlinx.serialization.json.add
+import java.net.DatagramPacket
+import java.net.Inet4Address
+import java.net.Inet6Address
+import java.net.InetAddress
+import java.net.InetSocketAddress
+import java.net.MulticastSocket
+import java.net.NetworkInterface
+import java.net.SocketAddress
+import java.net.SocketTimeoutException
+
+/**
+ * The listening half of every passive-discovery collector: hold a multicast lock, bind a
+ * well-known UDP port, join a group on every interface that will take it, and retain the datagrams
+ * that arrive until the window closes.
+ *
+ * Four things here are the difference between a working listener and one that silently reports an
+ * empty network, and each of them has cost somebody a day:
+ *
+ *  - **The MulticastLock.** Android's wifi stack filters out frames not addressed to this device
+ *    unless an app holds one. Without it every collector built on this returns "nothing on this
+ *    network" on a network full of chatter — the single most common reason a listener like this
+ *    appears to work and measures nothing. Whether it was actually held is therefore reported, not
+ *    assumed: an unheld lock plus silence is not a clean result and [outcome] refuses to call it one.
+ *  - **SO_REUSEADDR before bind.** The well-known discovery ports are shared by construction — the
+ *    system's own mDNS/SSDP responders and any other app doing this are already there — so binding
+ *    exclusively fails on exactly the networks worth measuring.
+ *  - **Joining per interface.** The group must be joined on the interface the traffic arrives on,
+ *    which is not necessarily the default route: a phone with wifi plus a VPN plus cellular has
+ *    three, and the LAN chatter is on the one that is not carrying the default route.
+ *  - **A bound buffer, bounded per source too.** A chatty network must not decide how much memory
+ *    this uses, and one device announcing every two seconds must not be able to fill the buffer and
+ *    hide the twenty quieter devices behind it. Both caps set [truncated] rather than being silent.
+ *
+ * Nothing here throws. Every failure lands in [failure] (the capture is dead) or [degraded] (it is
+ * running but cannot see everything), which the owning collector turns into a recorded status.
+ */
+internal class MulticastCapture(
+    /** Names the MulticastLock, so a `dumpsys wifi` during a run says which listener holds what. */
+    private val label: String,
+    private val port: Int,
+    private val group4: String? = null,
+    private val group6: String? = null,
+    private val maxPackets: Int = 400,
+    private val maxBytesRetained: Int = 128 * 1024,
+    private val maxPerSource: Int = 24,
+    /**
+     * Whether to fall back to an ephemeral port when the well-known one cannot be bound.
+     *
+     * Only useful for a protocol with an active half: replies to our own searches come back to
+     * whatever port we sent from, so an ephemeral socket still collects those — but it can never
+     * see the unsolicited announcements, which is why it is [degraded] and not normal operation.
+     */
+    private val allowEphemeralFallback: Boolean = false,
+) {
+
+    /** One retained datagram. Not a data class: the payload is a ByteArray, and structural equality
+     *  over it would be both wrong and expensive. */
+    class Packet(val sourceIp: String, val atMonoNs: Long, val data: ByteArray)
+
+    /** Set when the capture could not be brought up at all; the collector reports `unsupported`. */
+    var failure: String? = null
+        private set
+
+    /** Set when the capture is running but blind to part of what it exists to see. */
+    var degraded: String? = null
+        private set
+
+    var lockHeld: Boolean = false
+        private set
+
+    var boundPort: Int = 0
+        private set
+
+    var packetsSeen: Int = 0
+        private set
+
+    var truncated: Boolean = false
+        private set
+
+    val joined4 = ArrayList<String>()
+    val joined6 = ArrayList<String>()
+    private val joinErrors = ArrayList<String>()
+
+    /** Whether this protocol needs a group join at all — NetBIOS is broadcast, not multicast. */
+    private val expectsGroup = group4 != null || group6 != null
+
+    private val packets = ArrayList<Packet>()
+    private val perSource = HashMap<String, Int>()
+    private var retainedBytes = 0
+
+    @Volatile private var running = false
+    private var socket: MulticastSocket? = null
+    private var lock: WifiManager.MulticastLock? = null
+    private var scope: CoroutineScope? = null
+
+    /**
+     * Brings the listener up and returns whether it is capturing. Setup is a handful of syscalls,
+     * so it finishes in milliseconds and the [Collector.start] promptness contract holds; only the
+     * receive loop is handed to a background scope.
+     */
+    suspend fun start(ids: ProbeIds): Boolean = withContext(Dispatchers.IO) {
+        val s = bind() ?: return@withContext false
+        socket = s
+        running = true
+        // A degraded (ephemeral-port) socket is deliberately not joined to the group: it would be
+        // joining for a port nothing sends to, and the resulting "joined wlan0" in the evidence
+        // would claim a capability the capture does not have.
+        if (expectsGroup && degraded == null) joinGroups(s)
+        scope = CoroutineScope(SupervisorJob() + Dispatchers.IO).also { it.launch { pump(s, ids) } }
+        true
+    }
+
+    /** Acquires the multicast lock. Separate from [start] because it needs a Context and the rest
+     *  does not, and because whether it succeeded is itself evidence. */
+    fun acquireLock(ctx: Context) {
+        val wifi = runCatching { ctx.applicationContext.getSystemService(WifiManager::class.java) }
+            .getOrNull()
+        lock = runCatching {
+            wifi?.createMulticastLock("echolot-$label")?.apply {
+                setReferenceCounted(false)
+                acquire()
+            }
+        }.getOrNull()
+        lockHeld = runCatching { lock?.isHeld == true }.getOrDefault(false)
+    }
+
+    /** Sends from the capture socket, so replies land back in this capture rather than on a second
+     *  socket nobody is reading. Returns whether the datagram left the device. */
+    fun send(payload: ByteArray, host: String, toPort: Int): Boolean = runCatching {
+        val s = socket ?: return false
+        s.send(DatagramPacket(payload, payload.size, InetSocketAddress(host, toPort)))
+        true
+    }.getOrDefault(false)
+
+    /** Stops listening and hands back what was retained. Safe after a failed [start], and never
+     *  throws — a cancelled run still owes the caller the packets it did see. */
+    fun stop(): List<Packet> {
+        running = false
+        // Closed before the coroutine is cancelled: a blocking receive() does not notice
+        // cancellation, and closing the socket is what makes it return.
+        runCatching { socket?.close() }
+        socket = null
+        scope?.coroutineContext?.get(Job)?.cancel()
+        scope = null
+        runCatching { lock?.release() }
+        lock = null
+        // lockHeld deliberately survives the release: it records whether the capture *could* hear
+        // multicast while it ran, which is what [outcome] needs to decide whether silence is a
+        // fact about the network. Clearing it here would make every quiet network report that the
+        // lock was missing.
+        return synchronized(packets) { packets.toList() }
+    }
+
+    // ---- status ------------------------------------------------------------------------------
+
+    /**
+     * The status this capture's Test deserves, given whether anything was decoded.
+     *
+     * The interesting case is the last one. Silence on a network is a legitimate and useful
+     * finding — but only when we know the listener could have heard something. Without the
+     * multicast lock, or without a single successful group join, "nothing was seen" describes this
+     * app and not the network, and reporting it as `ok` would be the collector lying by omission.
+     */
+    fun outcome(sawAnything: Boolean): TestStatus = when {
+        failure != null -> TestStatus.UNSUPPORTED
+        degraded != null -> TestStatus.PARTIAL
+        sawAnything -> TestStatus.OK
+        expectsGroup && joined4.isEmpty() && joined6.isEmpty() -> TestStatus.PARTIAL
+        !lockHeld -> TestStatus.PARTIAL
+        else -> TestStatus.OK
+    }
+
+    /** Why [outcome] was not OK, in words, or null when it was. */
+    fun reason(sawAnything: Boolean): String? = when {
+        failure != null -> failure
+        degraded != null -> degraded
+        sawAnything -> null
+        expectsGroup && joined4.isEmpty() && joined6.isEmpty() ->
+            "no interface accepted the group join, so silence here says nothing about the network"
+        !lockHeld ->
+            "the wifi multicast lock was not held, so silence here says nothing about the network"
+        else -> null
+    }
+
+    /** The capture's own facts, for the collector's evidence. Every collector reports these
+     *  identically so that "saw nothing" can always be told apart from "could not listen". */
+    fun statusJson(): JsonObject = buildJsonObject {
+        put("multicast_lock", lockHeld)
+        put("bound_port", boundPort)
+        putJsonArray("joined_v4") { for (n in joined4) add(n) }
+        putJsonArray("joined_v6") { for (n in joined6) add(n) }
+        if (joinErrors.isNotEmpty()) {
+            put("join_errors", joinErrors.take(6).joinToString("; ").take(400))
+        }
+        degraded?.let { put("degraded", it) }
+        failure?.let { put("failure", it) }
+        put("packets_seen", packetsSeen)
+        put("packets_retained", synchronized(packets) { packets.size })
+        put("evidence_truncated", truncated)
+    }
+
+    // ---- internals ---------------------------------------------------------------------------
+
+    private fun bind(): MulticastSocket? {
+        // Unbound first, so SO_REUSEADDR is set *before* bind — setting it afterwards has no
+        // effect, and these ports are always already in use by something.
+        runCatching {
+            val s = MulticastSocket(null as SocketAddress?)
+            s.reuseAddress = true
+            s.bind(InetSocketAddress(port))
+            s.soTimeout = SO_TIMEOUT_MS
+            boundPort = port
+            return s
+        }.onFailure { first ->
+            val why = describe(first)
+            if (!allowEphemeralFallback) {
+                // Ports below 1024 are privileged on Android as on any Linux, so this is the
+                // expected outcome for NetBIOS and is a finding rather than a bug — see
+                // NetbiosCollector.
+                failure = "could not bind UDP $port: $why"
+                return null
+            }
+            runCatching {
+                val s = MulticastSocket(null as SocketAddress?)
+                s.reuseAddress = true
+                s.bind(InetSocketAddress(0))
+                s.soTimeout = SO_TIMEOUT_MS
+                boundPort = s.localPort
+                degraded = "UDP $port could not be bound ($why); listening on an ephemeral port " +
+                    "instead, so only replies to our own searches are visible and unsolicited " +
+                    "announcements are not"
+                return s
+            }.onFailure { failure = "could not bind UDP $port ($why) or any ephemeral port" }
+        }
+        return null
+    }
+
+    private fun joinGroups(s: MulticastSocket) {
+        val ifaces = runCatching { NetworkInterface.getNetworkInterfaces()?.toList() }
+            .getOrNull().orEmpty()
+            .filter {
+                runCatching { it.isUp && !it.isLoopback && it.supportsMulticast() }
+                    .getOrDefault(false)
+            }
+        val g4 = group4?.let { runCatching { InetAddress.getByName(it) }.getOrNull() }
+        val g6 = group6?.let { runCatching { InetAddress.getByName(it) }.getOrNull() }
+
+        for (ni in ifaces) {
+            val addrs = runCatching { ni.inetAddresses.toList() }.getOrNull().orEmpty()
+            if (g4 != null && addrs.any { it is Inet4Address }) {
+                join(s, g4, ni)?.let { joined4.add(it) }
+            }
+            // A network with no IPv6 address is not a failure to report as an error — it is a
+            // v4-only network, which is most of them. Only interfaces that could have joined are
+            // asked to.
+            if (g6 != null && addrs.any { it is Inet6Address }) {
+                join(s, g6, ni)?.let { joined6.add(it) }
+            }
+        }
+
+        // Last resort: let the kernel pick the interface. Some vendor builds refuse the explicit
+        // form on the very interface that carries the traffic, and a default-interface join is
+        // better than no listener at all.
+        if (joined4.isEmpty() && joined6.isEmpty()) {
+            @Suppress("DEPRECATION")
+            (g4 ?: g6)?.let { g ->
+                runCatching { s.joinGroup(g) }
+                    .onSuccess { (if (g is Inet4Address) joined4 else joined6).add("(default)") }
+                    .onFailure { joinErrors.add("default: ${describe(it)}") }
+            }
+        }
+    }
+
+    private fun join(s: MulticastSocket, group: InetAddress, ni: NetworkInterface): String? =
+        runCatching {
+            s.joinGroup(InetSocketAddress(group, boundPort), ni)
+            ni.name
+        }.onFailure {
+            joinErrors.add("${ni.name}/${if (group is Inet4Address) "v4" else "v6"}: ${describe(it)}")
+        }.getOrNull()
+
+    private fun pump(s: MulticastSocket, ids: ProbeIds) {
+        val buf = ByteArray(READ_BUFFER)
+        while (running) {
+            val p = DatagramPacket(buf, buf.size)
+            try {
+                s.receive(p)
+            } catch (t: SocketTimeoutException) {
+                // The timeout exists only so this loop notices `running` going false if the socket
+                // close somehow does not wake it. Nothing to record.
+                continue
+            } catch (t: Throwable) {
+                // The normal exit: stop() closed the socket underneath us. It is also what a
+                // vanishing interface looks like, and neither is worth a status of its own — the
+                // packets gathered so far are still the measurement.
+                return
+            }
+            packetsSeen++
+            val ip = p.address?.hostAddress ?: continue
+            val len = p.length
+            if (len <= 0) continue
+            synchronized(packets) {
+                val fromThis = perSource[ip] ?: 0
+                if (packets.size >= maxPackets ||
+                    retainedBytes + len > maxBytesRetained ||
+                    fromThis >= maxPerSource
+                ) {
+                    truncated = true
+                } else {
+                    packets.add(Packet(ip, ids.monoNs(), p.data.copyOf(len)))
+                    perSource[ip] = fromThis + 1
+                    retainedBytes += len
+                }
+            }
+        }
+    }
+
+    private companion object {
+        const val SO_TIMEOUT_MS = 1_000
+
+
+        /** Larger than any discovery datagram anyone sends; oversized ones are truncated by the
+         *  kernel, which the parsers survive by design. */
+        const val READ_BUFFER = 4_096
+
+        fun describe(t: Throwable): String =
+            (t.message ?: t.javaClass.simpleName).take(160)
+    }
+}
+
+/**
+ * The other half of what every discovery collector does: fold a stream of decoded messages into a
+ * deduplicated inventory of *things*, not packets.
+ *
+ * Deduplication is by source **and** identity, never by identity alone. Two devices announcing the
+ * same UPnP service type are two devices, and collapsing them would turn the one measurement worth
+ * having (how many things are on this segment) into a count of protocols. Conversely one device
+ * re-announcing every thirty seconds must not appear ten times — that is what [count] is for, and
+ * the repetition rate is itself readable from count over the window length.
+ *
+ * First-seen is kept on the monotonic clock per the two-clock rule: it answers "was this device
+ * here from the start, or did it appear four minutes in", which is exactly the question a long run
+ * exists to answer and the one a wall-clock stamp cannot be trusted for.
+ */
+internal class DiscoveryTable(private val maxEntries: Int = MAX_ENTRIES) {
+
+    private class Row(val firstSeenMonoNs: Long, val fields: JsonObject) {
+        var count = 0
+    }
+
+    private val rows = LinkedHashMap<Pair<String, String>, Row>()
+    private val sources = HashSet<String>()
+
+    /** True when a network was busy enough that entries had to be dropped — reported, never hidden. */
+    var overflowed = false
+        private set
+
+    /**
+     * [fields] is a lambda so the JSON for a repeat sighting is never built: on a chatty segment
+     * the overwhelming majority of packets are the same device saying the same thing again.
+     */
+    fun observe(sourceIp: String, identity: String, atMonoNs: Long, fields: () -> JsonObject) {
+        sources.add(sourceIp)
+        val key = sourceIp to identity
+        val existing = rows[key]
+        if (existing != null) {
+            existing.count++
+            return
+        }
+        if (rows.size >= maxEntries) {
+            overflowed = true
+            return
+        }
+        val built = buildJsonObject {
+            put("source_ip", sourceIp)
+            for ((k, v) in fields()) put(k, v)
+        }
+        rows[key] = Row(atMonoNs, built).also { it.count = 1 }
+    }
+
+    val distinctSources: Int get() = sources.size
+    val size: Int get() = rows.size
+    val isEmpty: Boolean get() = rows.isEmpty()
+
+    fun toJson(): kotlinx.serialization.json.JsonArray = kotlinx.serialization.json.JsonArray(
+        rows.values.map { r ->
+            JsonObject(
+                r.fields + mapOf(
+                    "first_seen_mono_ns" to kotlinx.serialization.json.JsonPrimitive(r.firstSeenMonoNs),
+                    "count" to kotlinx.serialization.json.JsonPrimitive(r.count),
+                )
+            )
+        }
+    )
+
+    private companion object {
+        /** Generous enough for any real segment, small enough that a broadcast storm cannot make
+         *  one test dominate the document. */
+        const val MAX_ENTRIES = 200
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/NetbiosCollector.kt

@@ -0,0 +1,131 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+
+/**
+ * local.netbios_inventory — NetBIOS name-service chatter (UDP 137) on this segment.
+ *
+ * NetBIOS name registration and query traffic is broadcast, not multicast, so there is no group to
+ * join: a socket bound to 137 sees it by being on the segment. Every packet carries a
+ * first-level-encoded name plus a suffix byte saying what the name is *for* — a workstation, a file
+ * server, a master browser — which makes a passive window over it a Windows-side inventory of the
+ * LAN, and, like LLMNR, a security observation in its own right: NBT-NS is the other half of the
+ * classic name-resolution spoofing surface.
+ *
+ * **Expect this to report `unsupported` on the app tier, and read that as a result rather than a
+ * bug.** 137 is below 1024, and Linux — Android included — reserves those ports for privileged
+ * processes; an unprivileged app UID cannot bind one. So the honest measurement here is usually
+ * "this tier cannot observe NetBIOS on this device", recorded with the exact bind error, rather
+ * than a silent absence that reads as a quiet network. The observation belongs to the Shizuku tier,
+ * whose shell UID can bind it; the collector is written now so that the decoder, the evidence shape
+ * and the registry id are settled and tested by the time that lands.
+ *
+ * An active alternative exists — send an NBSTAT query from an ephemeral port and read the unicast
+ * replies — and is deliberately not taken: it is a host sweep, which is scanning rather than
+ * measuring, and it would change what the run does to the network it is observing.
+ */
+class NetbiosCollector : BaseCollector() {
+
+    override val type = TestType.LOCAL_NETBIOS_INVENTORY
+    override val tier = Tier.APP
+
+    private val capture = MulticastCapture(
+        label = "netbios",
+        port = PORT,
+        // No group: NBT-NS is subnet broadcast. The multicast lock is still taken, because
+        // Android's wifi firmware filters broadcast as well as multicast under power save.
+        group4 = null,
+        group6 = null,
+        // Registration bursts repeat the same name several times a second; the per-source cap is
+        // what keeps one noisy Windows box from filling the buffer.
+        maxPerSource = 12,
+    )
+
+    private var startedAtMonoNs = 0L
+
+    override suspend fun start(ctx: Context, ids: ProbeIds) {
+        begin(ids)
+        startedAtMonoNs = ids.monoNs()
+        capture.acquireLock(ctx)
+        capture.start(ids)
+    }
+
+    override suspend fun stop(): Test {
+        val packets = capture.stop()
+
+        val table = DiscoveryTable()
+        var queries = 0
+        var registrations = 0
+        var undecodable = 0
+
+        for (p in packets) {
+            val n = NetbiosParser.parse(p.data, p.data.size)
+            if (n == null) {
+                undecodable++
+                continue
+            }
+            when (n.opcode) {
+                0 -> queries++
+                5, 8 -> registrations++
+            }
+            // Identity is name + suffix, not the name alone: one host registers the same name
+            // several times with different suffixes, and those are different facts about it.
+            table.observe(p.sourceIp, n.name + "#" + "%02X".format(n.suffix), p.atMonoNs) {
+                buildJsonObject {
+                    put("netbios_name", n.name)
+                    put("suffix", "0x%02X".format(n.suffix))
+                    put("role", n.role)
+                    put("operation", NetbiosParser.opcodeName(n.opcode))
+                    put("kind", if (n.isResponse) "response" else "request")
+                }
+            }
+        }
+
+        val evidence: JsonObject = buildJsonObject {
+            put("capture", capture.statusJson())
+            put("netbios_names", table.toJson())
+            put("evidence_truncated", capture.truncated || table.overflowed)
+        }
+        val metrics: JsonObject = buildJsonObject {
+            put("distinct_sources", table.distinctSources)
+            put("distinct_names", table.size)
+            put("packets", capture.packetsSeen)
+            put("name_queries", queries)
+            put("name_registrations", registrations)
+            put("undecodable_packets", undecodable)
+            put("netbios_in_use", table.distinctSources > 0)
+            put("truncated", capture.truncated || table.overflowed)
+        }
+        val saw = !table.isEmpty
+        return build(
+            capture.outcome(saw),
+            evidence = evidence,
+            metrics = metrics,
+            params = params(),
+            error = capture.reason(saw)?.let {
+                TestError(if (capture.failure != null) "port_unavailable" else "listen_incomplete", it)
+            },
+        )
+    }
+
+    private fun params(): JsonObject = buildJsonObject {
+        put("mode", "passive")
+        put("port", PORT)
+        put("transport", "udp broadcast")
+        put("started_mono_ns", startedAtMonoNs)
+    }
+
+    private companion object {
+        const val PORT = 137
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/NetworkChangeCollector.kt

@@ -0,0 +1,274 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import android.net.ConnectivityManager
+import android.net.LinkProperties
+import android.net.Network
+import android.net.NetworkCapabilities
+import android.net.NetworkRequest
+import app.echo_lot.measurement.NetworkChange
+import app.echo_lot.measurement.NetworkChanges
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import kotlinx.serialization.json.putJsonArray
+import kotlinx.serialization.json.addJsonObject
+import java.util.Collections
+
+/**
+ * Watches every network for the whole run and fills `networks[].changes[]` (measurement-schema §4).
+ *
+ * That array has been in the schema since the first draft and has never been populated, because
+ * nothing in a battery of one-shot probes is in a position to fill it. It is the single most
+ * valuable thing a long run adds: a wifi link that drops and returns mid-window is invisible to
+ * every probe — the ones before and after the gap both succeed — and it is exactly the fault people
+ * open a network diagnostic to chase.
+ *
+ * Reported as [TestType.LINK_IP_MONITOR] at app tier. The registry lists that type as Shizuku's
+ * (`ip monitor`), and this is deliberately the same observation from a tier that does not need it:
+ * link state as it changes over time. A document may therefore carry two `link.ip_monitor` tests,
+ * told apart by `tier` — which is what `tier` is for.
+ */
+class NetworkChangeCollector(
+    private val entries: List<NetworkInventory.Entry>,
+) : BaseCollector() {
+
+    override val type = TestType.LINK_IP_MONITOR
+    override val tier = Tier.APP
+
+    private data class Change(
+        val atMonoNs: Long,
+        val kind: String,
+        val event: String,
+        val iface: String,
+        val detail: String,
+    )
+
+    private val changes: MutableList<Change> = Collections.synchronizedList(mutableListOf())
+    private var cm: ConnectivityManager? = null
+    private var callback: ConnectivityManager.NetworkCallback? = null
+    private var registerError: String? = null
+
+    /**
+     * Last seen state per network, so only real changes are recorded.
+     *
+     * Both capability and link-property callbacks fire constantly on a live device — signal
+     * strength alone re-delivers capabilities every few seconds — and a five-minute window of that
+     * would bury the four events that matter under several hundred that do not. The first callback
+     * after a network appears is the baseline, not a change.
+     */
+    private val lastCaps = HashMap<String, String>()
+    private val lastLink = HashMap<String, String>()
+    /** Interface name per network handle, remembered because `onLost` can no longer look it up. */
+    private val ifaceOf = HashMap<String, String>()
+
+    /**
+     * The networks that were already up when the window opened.
+     *
+     * `registerNetworkCallback` replays `onAvailable` for every matching network the instant it is
+     * registered, so without this every run would open with three "the wifi appeared" events that
+     * describe the registration and not the network. A link that drops and returns comes back as a
+     * new handle, which is not in this set, so real re-appearances are still recorded.
+     */
+    private val seeded = HashSet<String>()
+
+    override suspend fun start(ctx: Context, ids: ProbeIds) {
+        begin(ids)
+        val manager = ctx.getSystemService(ConnectivityManager::class.java)
+        if (manager == null) {
+            registerError = "ConnectivityManager unavailable"
+            return
+        }
+        cm = manager
+        // Seed the interface names from the snapshot the run already took, so a network that is
+        // lost without ever having delivered a callback here is still attributable.
+        for (e in entries) {
+            e.model.iface?.let { ifaceOf[key(e.handle)] = it }
+            seeded.add(key(e.handle))
+        }
+
+        val cb = object : ConnectivityManager.NetworkCallback() {
+            override fun onAvailable(network: Network) {
+                val iface = resolveIface(network)
+                if (key(network) in seeded) return
+                record(ids, NetworkChanges.GAINED, "available", iface, "network became available")
+            }
+
+            override fun onLost(network: Network) {
+                val iface = ifaceOf[key(network)] ?: "(unknown)"
+                record(ids, NetworkChanges.LOST, "lost", iface, "network went away")
+                // Dropped so a returning link re-baselines instead of reporting every property it
+                // ever had as a change the moment it comes back.
+                lastCaps.remove(key(network)); lastLink.remove(key(network))
+            }
+
+            override fun onCapabilitiesChanged(network: Network, caps: NetworkCapabilities) {
+                val iface = resolveIface(network)
+                val print = capsFingerprint(caps)
+                val previous = lastCaps.put(key(network), print)
+                if (previous == null || previous == print) return
+                record(ids, NetworkChanges.LINK_CHANGED, "capabilities", iface, "$previous → $print")
+            }
+
+            override fun onLinkPropertiesChanged(network: Network, lp: LinkProperties) {
+                lp.interfaceName?.let { ifaceOf[key(network)] = it }
+                val print = linkFingerprint(lp)
+                val previous = lastLink.put(key(network), print)
+                if (previous == null || previous == print) return
+                record(ids, NetworkChanges.LINK_CHANGED, "link_properties", lp.interfaceName ?: "(unknown)",
+                    describeLinkDelta(previous, print))
+            }
+
+            override fun onLosing(network: Network, maxMsToLive: Int) {
+                val iface = ifaceOf[key(network)] ?: "(unknown)"
+                record(ids, NetworkChanges.LINK_CHANGED, "losing", iface, "about to be torn down in ${maxMsToLive} ms")
+            }
+        }
+        callback = cb
+        // clearCapabilities(), or the default request only matches INTERNET + NOT_RESTRICTED and
+        // the carrier's IMS/MMS networks — and, more importantly, a network in the middle of
+        // failing validation — never appear. The transports are named explicitly so this does not
+        // also follow whatever internal networks a vendor keeps in the list.
+        val request = NetworkRequest.Builder()
+            .clearCapabilities()
+            .addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
+            .addTransportType(NetworkCapabilities.TRANSPORT_CELLULAR)
+            .addTransportType(NetworkCapabilities.TRANSPORT_ETHERNET)
+            .addTransportType(NetworkCapabilities.TRANSPORT_VPN)
+            .build()
+        runCatching { manager.registerNetworkCallback(request, cb) }
+            .onFailure { registerError = it.message ?: it.javaClass.simpleName; callback = null }
+    }
+
+    override suspend fun stop(): Test {
+        callback?.let { cb -> runCatching { cm?.unregisterNetworkCallback(cb) } }
+        callback = null
+        val snapshot = synchronized(changes) { changes.toList() }
+
+        if (registerError != null) {
+            return build(
+                TestStatus.UNSUPPORTED,
+                error = TestError("callback_unavailable", registerError),
+            )
+        }
+
+        val evidence: JsonObject = buildJsonObject {
+            putJsonArray("changes") {
+                for (c in snapshot) addJsonObject {
+                    put("at_mono_ns", c.atMonoNs)
+                    put("kind", c.kind)
+                    put("event", c.event)
+                    put("interface", c.iface)
+                    put("detail", c.detail)
+                }
+            }
+        }
+        val perIface = snapshot.groupBy { it.iface }
+        val metrics: JsonObject = buildJsonObject {
+            put("changes_total", snapshot.size)
+            put("networks_lost", snapshot.count { it.kind == NetworkChanges.LOST })
+            put("networks_gained", snapshot.count { it.event == "available" })
+            put("link_changes", snapshot.count { it.kind == NetworkChanges.LINK_CHANGED })
+            // The number a reader actually wants: how many times a link went away and came back.
+            // Counted by the same function the flapping finding uses, so the metric and the
+            // finding can never tell different stories about one window.
+            put("flap_cycles", perIface.values.sumOf { NetworkChanges.flapCycles(it.map { c -> c.kind }) })
+        }
+        // Zero changes over the window is a real, useful result — a stable network — so it is OK
+        // rather than a failure. The window that produced it is what makes that mean anything, and
+        // it is recorded in run.mode plus the sibling collectors' params.
+        return build(TestStatus.OK, evidence = evidence, metrics = metrics)
+    }
+
+    /**
+     * The changes belonging to each network in `networks[]`, keyed by its model id.
+     *
+     * Matched by interface name rather than by Android's `Network` handle, because a link that
+     * drops and returns comes back as a *different* handle with the same interface — and the
+     * flapping case is precisely the one this must not lose. Changes on an interface that was not
+     * in the run's initial snapshot stay in the test evidence but have no `networks[]` entry to
+     * hang from.
+     */
+    fun changesByNetwork(): Map<String, List<NetworkChange>> {
+        val byIface = entries.mapNotNull { e -> e.model.iface?.let { it to e.model.id } }.toMap()
+        val out = LinkedHashMap<String, MutableList<NetworkChange>>()
+        for (c in synchronized(changes) { changes.toList() }) {
+            val id = byIface[c.iface] ?: continue
+            out.getOrPut(id) { mutableListOf() }.add(
+                NetworkChange(
+                    atMonoNs = c.atMonoNs,
+                    kind = c.kind,
+                    detail = buildJsonObject {
+                        put("event", c.event)
+                        put("interface", c.iface)
+                        put("detail", c.detail)
+                    },
+                )
+            )
+        }
+        return out
+    }
+
+    private fun record(ids: ProbeIds, kind: String, event: String, iface: String, detail: String) {
+        changes.add(Change(ids.monoNs(), kind, event, iface, detail))
+    }
+
+    private fun resolveIface(network: Network): String {
+        val known = ifaceOf[key(network)]
+        if (known != null) return known
+        val name = runCatching { cm?.getLinkProperties(network)?.interfaceName }.getOrNull()
+        if (name != null) ifaceOf[key(network)] = name
+        return name ?: "(unknown)"
+    }
+
+    private companion object {
+        /** Android's own network id, stable for the life of one Network object. */
+        private fun key(n: Network): String = n.toString()
+
+        /**
+         * Only the capabilities whose change means something diagnostically.
+         *
+         * Bandwidth estimates and signal strength are deliberately excluded: they change every few
+         * seconds on a moving device, and including them turns a change log into a sampling log.
+         * VALIDATED and CAPTIVE_PORTAL are the two that matter most — they are the moment Android
+         * decides a network does or does not carry the internet.
+         */
+        private fun capsFingerprint(c: NetworkCapabilities): String = buildString {
+            fun flag(name: String, cap: Int) {
+                if (runCatching { c.hasCapability(cap) }.getOrDefault(false)) append(name).append(' ')
+            }
+            flag("internet", NetworkCapabilities.NET_CAPABILITY_INTERNET)
+            flag("validated", NetworkCapabilities.NET_CAPABILITY_VALIDATED)
+            flag("captive", NetworkCapabilities.NET_CAPABILITY_CAPTIVE_PORTAL)
+            flag("not-metered", NetworkCapabilities.NET_CAPABILITY_NOT_METERED)
+            flag("not-suspended", NET_CAPABILITY_NOT_SUSPENDED)
+            flag("not-restricted", NetworkCapabilities.NET_CAPABILITY_NOT_RESTRICTED)
+        }.trim().ifEmpty { "(none)" }
+
+        /** NetworkCapabilities.NET_CAPABILITY_NOT_SUSPENDED, API 28+ (@SystemApi constant). */
+        private const val NET_CAPABILITY_NOT_SUSPENDED = 21
+
+        private fun linkFingerprint(lp: LinkProperties): String {
+            val addrs = lp.linkAddresses.map { it.toString() }.sorted().joinToString(",")
+            val routes = lp.routes.map { it.toString() }.sorted().joinToString(",")
+            val dns = lp.dnsServers.mapNotNull { it.hostAddress }.sorted().joinToString(",")
+            return "mtu=${lp.mtu}|addr=$addrs|route=$routes|dns=$dns"
+        }
+
+        /** Names which part of the link changed, so the detail is readable without a diff tool. */
+        private fun describeLinkDelta(before: String, after: String): String {
+            val b = before.split('|'); val a = after.split('|')
+            val changed = b.indices.filter { it < a.size && b[it] != a[it] }
+                .map { a[it].substringBefore('=') }
+            return if (changed.isEmpty()) "changed" else "changed: ${changed.joinToString(", ")}"
+        }
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/NetworkInventory.kt

@@ -39,6 +39,46 @@ object NetworkInventory {
         return out
     }
 
+    /**
+     * Android's own verdict on the network, read straight from the capabilities it already has.
+     *
+     * PARTIAL_CONNECTIVITY only exists from API 28 and CAPTIVE_PORTAL from 23, so both are read
+     * defensively: an older platform that cannot answer should leave the field null rather than
+     * assert a false.
+     */
+    private fun systemVerdict(caps: NetworkCapabilities): app.echo_lot.measurement.SystemVerdict =
+        app.echo_lot.measurement.SystemVerdict(
+            validated = caps.hasCapability(NetworkCapabilities.NET_CAPABILITY_VALIDATED),
+            captivePortal = runCatching {
+                caps.hasCapability(NetworkCapabilities.NET_CAPABILITY_CAPTIVE_PORTAL)
+            }.getOrNull(),
+            // NET_CAPABILITY_PARTIAL_CONNECTIVITY is @SystemApi, so the constant is not in the
+            // public SDK even though the platform sets it from API 28. The number is stable —
+            // changing it would break every system app that reads it — but this is a value the
+            // SDK does not promise us, so it is asked for defensively and reported as unknown
+            // rather than as false if anything about it is not as expected.
+            partialConnectivity = runCatching {
+                caps.hasCapability(NET_CAPABILITY_PARTIAL_CONNECTIVITY)
+            }.getOrNull(),
+        )
+
+    /** @SystemApi NetworkCapabilities.NET_CAPABILITY_PARTIAL_CONNECTIVITY, API 28+. */
+    private const val NET_CAPABILITY_PARTIAL_CONNECTIVITY = 24
+
+    /**
+     * Can an ordinary app send on this network?
+     *
+     * The carrier's special-purpose networks (IMS/VoLTE, MMS, XCAP) sit in `allNetworks` next to
+     * the real ones, carrying `IMS`/`MMS` but neither `INTERNET` nor `NOT_RESTRICTED`. Binding
+     * to them fails with EPERM forever, because it needs `CONNECTIVITY_USE_RESTRICTED_NETWORKS`
+     * — signature-level, unobtainable for this app. Asking the capabilities up front is what
+     * separates "the OS will never let us measure this" from "something is blocking us", which
+     * a bind attempt alone cannot distinguish and which the constraint logic must not confuse.
+     */
+    private fun appUsable(caps: NetworkCapabilities): Boolean =
+        caps.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET) &&
+            caps.hasCapability(NetworkCapabilities.NET_CAPABILITY_NOT_RESTRICTED)
+
     private fun toModel(id: String, caps: NetworkCapabilities, lp: LinkProperties): MNetwork {
         val transport = when {
             caps.hasTransport(NetworkCapabilities.TRANSPORT_WIFI) -> Transport.WIFI
@@ -72,6 +112,8 @@ object NetworkInventory {
         return MNetwork(
             id = id, transport = transport, iface = lp.interfaceName,
             link = Link(mtu = lp.mtu.takeIf { it > 0 }, addresses = addresses, routes = routes, dns = dns),
+            systemVerdict = systemVerdict(caps),
+            appUsable = appUsable(caps),
         )
     }
 }

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/OsAbi.kt

@@ -0,0 +1,70 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.system.Os
+import java.io.FileDescriptor
+
+/**
+ * Linux socket-option ABI numbers that android.system.OsConstants does NOT reliably expose.
+ * Stable across Android's supported ABIs at the IP/IPv6 protocol levels, which is why they can
+ * be hardcoded: if setsockoptInt with one of these succeeds, the kernel accepted the option; if
+ * it throws ErrnoException, it did not. Either outcome is data. Do not "fix" these to
+ * OsConstants names — they don't exist there (validated in the prober; see its OsAbi.kt).
+ *
+ * Measured fact worth keeping: `Os.getsockoptInt` is absent on both known devices (OnePlus 15
+ * A16, Lenovo TB330FU A15), so path-MTU values must be read from the errqueue (`ee_info`), never
+ * from getsockopt(IP_MTU).
+ */
+object OsAbi {
+    // IP level
+    const val IP_TTL = 2
+    const val IP_MTU_DISCOVER = 10
+    const val IP_MTU = 14
+    const val IP_RECVERR = 11
+    const val IP_PMTUDISC_DO = 2      // set DF, honor PMTU
+    const val IP_PMTUDISC_PROBE = 3   // set DF, ignore PMTU (for probing)
+
+    // IPv6 level
+    const val IPV6_MTU_DISCOVER = 23
+    const val IPV6_MTU = 24
+    const val IPV6_RECVERR = 25
+    const val IPV6_UNICAST_HOPS = 16
+    const val IPV6_PMTUDISC_PROBE = 3
+
+    // recv flags — not in OsConstants on any current API level
+    const val MSG_ERRQUEUE = 0x2000
+    const val MSG_DONTWAIT = 0x40
+
+    // struct sock_extended_err (uapi/linux/errqueue.h), fixed layout on all Android ABIs:
+    // u32 ee_errno; u8 ee_origin; u8 ee_type; u8 ee_code; u8 ee_pad; u32 ee_info; u32 ee_data;
+    // followed directly by the offender sockaddr (SO_EE_OFFENDER).
+    const val SOCK_EE_SIZE = 16
+    const val SO_EE_ORIGIN_ICMP = 2
+    const val ICMP_TIME_EXCEEDED = 11
+    const val ICMP_DEST_UNREACH = 3
+
+    /** Try setsockoptInt; return null on success, or the errno name on failure. */
+    fun trySetIntOpt(fd: FileDescriptor, level: Int, opt: Int, value: Int): String? =
+        try {
+            Os.setsockoptInt(fd, level, opt, value)
+            null
+        } catch (e: Throwable) {
+            e.message ?: e.javaClass.simpleName
+        }
+
+    /**
+     * getsockoptInt is not part of the stable public Os surface on every API level, so it is
+     * reached via reflection; callers must treat failure as "unreadable", not as an error.
+     */
+    fun tryGetIntOpt(fd: FileDescriptor, level: Int, opt: Int): Result<Int> = runCatching {
+        val m = Os::class.java.getMethod(
+            "getsockoptInt",
+            FileDescriptor::class.java,
+            Int::class.javaPrimitiveType,
+            Int::class.javaPrimitiveType,
+        )
+        m.invoke(null, fd, level, opt) as Int
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/PingSeriesCollector.kt

@@ -0,0 +1,158 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.isActive
+import kotlinx.coroutines.launch
+import kotlinx.serialization.json.JsonNull
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import kotlinx.serialization.json.putJsonArray
+import kotlinx.serialization.json.add
+import java.util.Collections
+
+/**
+ * icmp.ping4 sampled across the window — loss and jitter over minutes instead of one packet.
+ *
+ * The battery's [IcmpProbe] answers "does this network reply at all", which one echo can settle.
+ * It cannot answer "how often does it not", and that is the complaint people actually have:
+ * 2 % loss is invisible to a single ping and ruins a video call. A series over five minutes also
+ * catches loss that comes in bursts, which an average taken over ten packets in one second cannot
+ * distinguish from a clean link.
+ *
+ * Emitted as its own `icmp.ping4` test alongside the battery's. `params` carries the window and
+ * the interval precisely so the two are never mistaken for each other — a reader seeing 300 sent
+ * packets in one and 1 in the other must be able to tell which is which without guessing.
+ *
+ * Sustained loss here deliberately emits **no finding**. Every loss code in the registry is about
+ * the server path — `connectivity.udp_loss` and its directional siblings all say "UDP", and they
+ * mean the probe protocol's traffic, whose direction the server can attest to. ICMP echo to a
+ * public address is a different measurement with a different set of benign explanations (rate
+ * limiting at the target is the obvious one), and borrowing a code that claims otherwise would put
+ * two unrelated things under one dashboard entry — the exact failure the registry exists to
+ * prevent. The metrics say what was seen; a code for it can be added when it has been defined.
+ */
+class PingSeriesCollector(
+    private val target: String = "1.1.1.1",
+    private val intervalMs: Long = 2_000,
+    /** Deliberately below [intervalMs]: a reply that arrives after the next probe was due is lost
+     *  for any practical purpose, and waiting for it would make the series drift out of cadence. */
+    private val timeoutMs: Int = 1_500,
+) : BaseCollector() {
+
+    override val type = TestType.ICMP_PING4
+    override val tier = Tier.APP
+
+    private val txMonoNs: MutableList<Long> = Collections.synchronizedList(mutableListOf())
+    private val rttMs: MutableList<Double?> = Collections.synchronizedList(mutableListOf())
+    private var notSent = 0
+    private var scope: CoroutineScope? = null
+    private var startedAtMonoNs = 0L
+
+    override suspend fun start(ctx: Context, ids: ProbeIds) {
+        begin(ids)
+        startedAtMonoNs = ids.monoNs()
+        // The default network, and only the default network: this measures what the device's own
+        // traffic experiences over the window. Per-network binding is the battery's job, and doing
+        // it here would multiply the packet rate by the number of interfaces for no new answer.
+        val s = CoroutineScope(SupervisorJob() + Dispatchers.IO).also { scope = it }
+        s.launch {
+            var seq = 1
+            while (isActive) {
+                val t0 = ids.monoNs()
+                val r = IcmpEcho.ping(null, target, v6 = false, timeoutMs = timeoutMs, seq = seq)
+                if (r.attempted) {
+                    txMonoNs.add(t0)
+                    rttMs.add(r.rttMs)
+                } else {
+                    // Never left the device — a socket or bind failure is not packet loss, and
+                    // counting it as loss would blame the network for the app's own trouble.
+                    notSent++
+                }
+                seq = (seq + 1) and 0xFFFF
+                delay(intervalMs)
+            }
+        }
+    }
+
+    override suspend fun stop(): Test {
+        scope?.coroutineContext?.get(Job)?.cancel()
+        scope = null
+
+        val tx = synchronized(txMonoNs) { txMonoNs.toList() }
+        val rtt = synchronized(rttMs) { rttMs.toList() }
+        val received = rtt.filterNotNull()
+
+        val evidence: JsonObject = buildJsonObject {
+            putJsonArray("seq") { for (i in tx.indices) add(i) }
+            putJsonArray("t_tx_ns") { for (v in tx) add(v) }
+            // null at an index is a lost probe, per the §6.2 columnar convention.
+            putJsonArray("rtt_ms") {
+                for (v in rtt) add(v?.let { JsonPrimitive(round1(it)) } ?: JsonNull)
+            }
+        }
+        val metrics: JsonObject = buildJsonObject {
+            put("sent", tx.size)
+            put("received", received.size)
+            put("not_sent", notSent)
+            if (tx.isNotEmpty()) {
+                put("loss_pct", round1((tx.size - received.size) * 100.0 / tx.size))
+            }
+            if (received.isNotEmpty()) {
+                put("rtt_ms_min", round1(received.min()))
+                put("rtt_ms_avg", round1(received.average()))
+                put("rtt_ms_max", round1(received.max()))
+                put("jitter_ms", round1(meanDeviation(received)))
+            }
+        }
+        val status = when {
+            tx.isEmpty() -> TestStatus.UNSUPPORTED
+            received.isEmpty() -> TestStatus.FAILED
+            received.size < tx.size -> TestStatus.PARTIAL
+            else -> TestStatus.OK
+        }
+        return build(status, evidence = evidence, metrics = metrics, params = params())
+    }
+
+    private fun params(): JsonObject = buildJsonObject {
+        // What separates this from the battery's single ping, and what a reader needs to reproduce
+        // it. Without these two numbers "300 packets, 2 % loss" is a rate nobody can interpret.
+        put("mode", "series")
+        put("target", target)
+        put("interval_ms", intervalMs)
+        put("timeout_ms", timeoutMs)
+        put("started_mono_ns", startedAtMonoNs)
+        put("network", "default")
+    }
+
+    private companion object {
+        fun round1(v: Double) = Math.round(v * 10.0) / 10.0
+
+        /**
+         * Mean deviation between consecutive round trips — jitter as a stream experiences it.
+         *
+         * Not the spread around the average: a link that alternates 20 ms / 200 ms and one that
+         * drifts slowly from 20 ms to 200 ms have the same standard deviation, and only the first
+         * one breaks a call.
+         */
+        fun meanDeviation(values: List<Double>): Double {
+            if (values.size < 2) return 0.0
+            var sum = 0.0
+            for (i in 1 until values.size) sum += kotlin.math.abs(values[i] - values[i - 1])
+            return sum / (values.size - 1)
+        }
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/Probe.kt

@@ -55,9 +55,10 @@ class TestBuilder(
         evidence: JsonObject? = null,
         metrics: JsonObject? = null,
         error: TestError? = null,
+        params: JsonObject? = null,
     ): Test = Test(
         id = id, type = type, networkRef = networkRef, sessionRef = sessionRef, tier = tier,
         startedMonoNs = startedMonoNs, endedMonoNs = ids.monoNs(),
-        status = status, error = error, evidence = evidence, metrics = metrics,
+        status = status, error = error, params = params, evidence = evidence, metrics = metrics,
     )
 }

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/ProbeCollector.kt

@@ -0,0 +1,69 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestStatus
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Deferred
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.async
+import kotlinx.coroutines.withTimeoutOrNull
+
+/**
+ * Runs an ordinary [Probe] beside the battery instead of inside it.
+ *
+ * Some probes are already listeners with a fixed window — [MdnsInventoryProbe] does nothing but
+ * wait for answers — and in a long run their window should be the run's window. Running them in
+ * the sequential battery would then stall every probe behind them for five minutes, which is a
+ * scheduling problem and not a measurement one, so the fix is to move them rather than to shorten
+ * them.
+ *
+ * Durations are deliberately *not* fed back into the estimate learning: a probe that listens for
+ * the whole window would teach the short-mode progress bar that mDNS discovery takes five minutes.
+ */
+class ProbeCollector(private val probe: Probe) : BaseCollector() {
+
+    override val type get() = probe.type
+    override val tier get() = probe.tier
+
+    private var scope: CoroutineScope? = null
+    private var running: Deferred<Test>? = null
+
+    override suspend fun start(ctx: Context, ids: ProbeIds) {
+        begin(ids)
+        val s = CoroutineScope(SupervisorJob() + Dispatchers.IO).also { scope = it }
+        running = s.async { probe.run(ctx, ids) }
+    }
+
+    override suspend fun stop(): Test {
+        val job = running
+        running = null
+        val finished = job?.let {
+            // A short grace, not a long one. A probe timed to the window has already finished by
+            // the time this is called, so the normal path returns instantly; the grace only covers
+            // it being slightly late. It is deliberately kept to a second and a half because the
+            // other caller is the Cancel button, where every millisecond spent waiting for a
+            // listener that will not finish is a millisecond the user watches nothing happen.
+            withTimeoutOrNull(GRACE_MS) { runCatching { it.await() }.getOrNull() }
+        }
+        scope?.coroutineContext?.get(Job)?.cancel()
+        scope = null
+        return finished ?: build(
+            TestStatus.PARTIAL,
+            error = TestError(
+                "window_closed",
+                "the run's window ended before this listener finished",
+            ),
+        )
+    }
+
+    private companion object {
+        const val GRACE_MS = 1_500L
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/SsdpCollector.kt

@@ -0,0 +1,181 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.isActive
+import kotlinx.coroutines.launch
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+
+/**
+ * local.ssdp_inventory — what UPnP/SSDP devices are on this segment, gathered over the whole window.
+ *
+ * **Both halves are needed, and neither is sufficient.** Passive listening catches ssdp:alive and
+ * ssdp:byebye announcements, which is the only way to see a device that ignores searches (plenty
+ * do, deliberately) and the only way to see one leave. But announcements are periodic and sparse —
+ * a device re-announces on its own cache-control interval, commonly 30 minutes — so a five-minute
+ * passive window silently misses most of the segment. An M-SEARCH provokes an immediate reply from
+ * everything that is listening, which is most things, and catches the quiet ones. Running only the
+ * active half is what [RouterIdentityProbe] already does in the battery, and it is why that probe
+ * cannot tell you that a device disappeared halfway through the run.
+ *
+ * The searches are paced, not flooded: [maxSearches] of them spread [searchIntervalMs] apart. A
+ * repeat catches devices that joined the network after the run started or were asleep at t=0, while
+ * staying orders of magnitude below a rate that would itself perturb the network being measured —
+ * the tool must not become the fault it is looking for. `upnp:rootdevice` rather than `ssdp:all`
+ * for the same reason: one reply per device instead of one per service.
+ *
+ * The searches go out from the capture socket bound to 1900, so unicast replies land in the same
+ * capture as the multicast announcements rather than needing a second socket nobody is reading.
+ */
+class SsdpCollector(
+    private val searchIntervalMs: Long = 60_000,
+    private val maxSearches: Int = 5,
+) : BaseCollector() {
+
+    override val type = TestType.LOCAL_SSDP_INVENTORY
+    override val tier = Tier.APP
+
+    private val capture = MulticastCapture(
+        label = "ssdp",
+        port = PORT,
+        group4 = GROUP4,
+        // The IPv6 link-local SSDP group. Free to join where IPv6 exists and skipped where it does
+        // not, so a v4-only network costs nothing and a v6-only device is not invisible.
+        group6 = GROUP6,
+        // SSDP is the chattiest of the four; a device announcing every service it hosts can emit a
+        // dozen NOTIFYs per cycle, so the per-source cap does most of the work here.
+        maxPackets = 600,
+        // The only one of the four with an active half worth keeping when 1900 is taken.
+        allowEphemeralFallback = true,
+    )
+
+    private var scope: CoroutineScope? = null
+    private var searchesSent = 0
+    private var startedAtMonoNs = 0L
+
+    override suspend fun start(ctx: Context, ids: ProbeIds) {
+        begin(ids)
+        startedAtMonoNs = ids.monoNs()
+        capture.acquireLock(ctx)
+        if (!capture.start(ids)) return
+
+        val s = CoroutineScope(SupervisorJob() + Dispatchers.IO).also { scope = it }
+        s.launch {
+            while (isActive && searchesSent < maxSearches) {
+                if (capture.send(MSEARCH, GROUP4, PORT)) searchesSent++ else break
+                delay(searchIntervalMs)
+            }
+        }
+    }
+
+    override suspend fun stop(): Test {
+        scope?.coroutineContext?.get(Job)?.cancel()
+        scope = null
+        val packets = capture.stop()
+
+        val table = DiscoveryTable()
+        var alive = 0
+        var byebye = 0
+        var responses = 0
+        var undecodable = 0
+
+        for (p in packets) {
+            val msg = SsdpParser.parse(p.data, p.data.size)
+            if (msg == null) {
+                undecodable++
+                continue
+            }
+            when (msg.kind) {
+                SsdpKind.ALIVE -> alive++
+                SsdpKind.BYEBYE -> byebye++
+                SsdpKind.RESPONSE -> responses++
+                // Our own M-SEARCH comes back to us through the group; counting it as a device
+                // would inventory the phone doing the measuring.
+                SsdpKind.SEARCH -> continue
+                else -> Unit
+            }
+            // USN is the device+service identity SSDP itself uses; NT/ST is the fallback for
+            // devices that omit it, and the source IP already separates two devices offering the
+            // same service type.
+            val identity = msg.usn ?: msg.target ?: "(unidentified)"
+            table.observe(p.sourceIp, identity, p.atMonoNs) {
+                buildJsonObject {
+                    put("usn", identity)
+                    msg.target?.let { put("target", it) }
+                    msg.serverBanner?.let { put("server_banner", it) }
+                    SsdpParser.productHint(msg.serverBanner)?.let { put("product_hint", it) }
+                    msg.location?.let { put("location", it) }
+                    put("kind", msg.kind.name.lowercase())
+                }
+            }
+        }
+
+        val evidence: JsonObject = buildJsonObject {
+            put("capture", capture.statusJson())
+            put("ssdp_devices", table.toJson())
+            // Two truncation sources, reported apart: the capture dropping datagrams and the
+            // inventory dropping distinct entries mean different things about the network.
+            put("evidence_truncated", capture.truncated || table.overflowed)
+        }
+        val metrics: JsonObject = buildJsonObject {
+            put("distinct_sources", table.distinctSources)
+            put("distinct_advertisements", table.size)
+            put("packets", capture.packetsSeen)
+            put("alive", alive)
+            put("byebye", byebye)
+            put("search_responses", responses)
+            put("undecodable_packets", undecodable)
+            put("searches_sent", searchesSent)
+            put("truncated", capture.truncated || table.overflowed)
+        }
+        val status = capture.outcome(sawAnything = !table.isEmpty)
+        val reason = capture.reason(sawAnything = !table.isEmpty)
+        return build(
+            status,
+            evidence = evidence,
+            metrics = metrics,
+            params = params(),
+            error = reason?.let { TestError("listen_incomplete", it) },
+        )
+    }
+
+    private fun params(): JsonObject = buildJsonObject {
+        put("mode", "passive+msearch")
+        put("group_v4", "$GROUP4:$PORT")
+        put("group_v6", "[$GROUP6]:$PORT")
+        put("search_target", SEARCH_TARGET)
+        put("search_interval_ms", searchIntervalMs)
+        put("max_searches", maxSearches)
+        put("started_mono_ns", startedAtMonoNs)
+    }
+
+    private companion object {
+        const val PORT = 1900
+        const val GROUP4 = "239.255.255.250"
+        const val GROUP6 = "ff02::c"
+        const val SEARCH_TARGET = "upnp:rootdevice"
+
+        /** MX is the maximum random delay a responder waits, in seconds. 3 spreads the replies
+         *  enough that a segment full of devices does not answer in one burst we then drop. */
+        val MSEARCH: ByteArray = (
+            "M-SEARCH * HTTP/1.1\r\n" +
+                "HOST: $GROUP4:$PORT\r\n" +
+                "MAN: \"ssdp:discover\"\r\n" +
+                "MX: 3\r\n" +
+                "ST: $SEARCH_TARGET\r\n\r\n"
+            ).toByteArray(Charsets.ISO_8859_1)
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/StunProbe.kt

@@ -60,6 +60,15 @@ class StunProbe(
 
     override suspend fun run(ctx: Context, ids: ProbeIds): Test = withContext(Dispatchers.IO) {
         val b = TestBuilder(type, tier, ids)
+        // Without a server there is nothing to ask. Skipped rather than failed: "the STUN test
+        // failed" reads as a finding about the network, when the truth is that this device is
+        // not enrolled anywhere and no packet was ever sent.
+        if (serverHost.isBlank()) {
+            return@withContext b.build(
+                TestStatus.SKIPPED,
+                evidence = buildJsonObject { put("reason", "no server configured to ask") },
+            )
+        }
         DatagramSocket().use { sock ->
             sock.soTimeout = 3000
             val localPort = sock.localPort

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/TracerouteProbe.kt

@@ -0,0 +1,255 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import android.system.Os
+import android.system.OsConstants
+import app.echo_lot.measurement.Flow
+import app.echo_lot.measurement.Hop
+import app.echo_lot.measurement.HopProbe
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import app.echo_lot.measurement.TracerouteEvidence
+import app.echo_lot.measurement.toEvidence
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import java.io.FileDescriptor
+import java.net.InetAddress
+import java.net.InetSocketAddress
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
+
+/**
+ * traceroute.udp4 — UDP traceroute reading ICMP time-exceeded off the socket error queue via
+ * Os.recvmsg(MSG_ERRQUEUE): no root, no raw socket, no native code. Folded from the prober,
+ * which validated real hop addresses on both known devices (6 hops on the OnePlus 15, 5 on the
+ * Lenovo) and thereby retired the planned C-over-JNI errqueue shim.
+ *
+ * StructMsghdr/StructCmsghdr/recvmsg are reached via reflection (repo convention for uncertain
+ * OS paths): present since roughly API 34, absent before, and the probe must run — and report —
+ * on both. An absent API is UNSUPPORTED with the reason, never a crash.
+ */
+class TracerouteProbe(
+    private val targetHost: String = "1.1.1.1",
+    private val maxHops: Int = 6,
+) : Probe {
+    override val type = TestType.TRACEROUTE_UDP4
+    override val tier = Tier.APP
+    // Validated wall clock is ~250 ms on a healthy path; the ceiling is maxHops silent hops at
+    // 900 ms each, which only a blackholing path produces.
+    override val estimatedMs = 1_500L
+
+    private companion object {
+        const val BASE_PORT = 33434
+        /** ICMP errors take one RTT to surface on the errqueue; poll briefly, never block. */
+        const val HOP_DEADLINE_NS = 900_000_000L
+        const val POLL_INTERVAL_MS = 40L
+    }
+
+    override suspend fun run(ctx: Context, ids: ProbeIds): Test = withContext(Dispatchers.IO) {
+        val b = TestBuilder(type, tier, ids)
+        val params = buildJsonObject {
+            put("target", targetHost); put("max_hops", maxHops); put("base_port", BASE_PORT)
+        }
+
+        val api = ErrqueueApi.resolve()
+            ?: return@withContext b.build(
+                TestStatus.UNSUPPORTED,
+                params = params,
+                error = TestError(
+                    "no_recvmsg",
+                    "StructMsghdr/Os.recvmsg not on this API level — errqueue unreadable",
+                ),
+            )
+
+        var fd: FileDescriptor? = null
+        try {
+            fd = Os.socket(OsConstants.AF_INET, OsConstants.SOCK_DGRAM, OsConstants.IPPROTO_UDP)
+            OsAbi.trySetIntOpt(fd, OsConstants.IPPROTO_IP, OsAbi.IP_RECVERR, 1)?.let {
+                return@withContext b.build(
+                    TestStatus.UNSUPPORTED,
+                    params = params,
+                    error = TestError("ip_recverr_rejected", it),
+                )
+            }
+            val target = InetAddress.getByName(targetHost)
+
+            val hops = ArrayList<Hop>(maxHops)
+            var hopsSeen = 0
+            var reachedTarget = false
+            var srcPort = 0
+            for (ttl in 1..maxHops) {
+                OsAbi.trySetIntOpt(fd, OsConstants.IPPROTO_IP, OsAbi.IP_TTL, ttl)
+                val t0 = System.nanoTime()
+                val sent = runCatching {
+                    Os.sendto(fd, ByteArray(32), 0, 32, 0, target, BASE_PORT + ttl)
+                }
+                if (sent.isFailure) {
+                    hops.add(Hop(ttl, listOf(HopProbe(icmp = "sendto failed: " +
+                        (sent.exceptionOrNull()?.message ?: "?")))))
+                    continue
+                }
+                if (srcPort == 0) {
+                    // Only readable after the implicit bind the first send performs.
+                    srcPort = runCatching {
+                        (Os.getsockname(fd) as? InetSocketAddress)?.port ?: 0
+                    }.getOrDefault(0)
+                }
+
+                var hop: ErrqueueApi.ErrEvent? = null
+                val deadline = System.nanoTime() + HOP_DEADLINE_NS
+                while (hop == null && System.nanoTime() < deadline) {
+                    hop = api.pollErrqueue(fd)
+                    if (hop == null) delay(POLL_INTERVAL_MS)
+                }
+                val rttNs = System.nanoTime() - t0
+                when {
+                    hop == null -> hops.add(Hop(ttl, listOf(HopProbe()))) // silent hop: all null
+                    hop.parseError != null ->
+                        hops.add(Hop(ttl, listOf(HopProbe(icmp = "unparsed: ${hop.parseError}"))))
+                    else -> {
+                        hopsSeen++
+                        hops.add(Hop(ttl, listOf(HopProbe(
+                            replyFrom = hop.offender,
+                            rttNs = rttNs,
+                            icmp = when (hop.icmpType) {
+                                OsAbi.ICMP_TIME_EXCEEDED -> "time_exceeded"
+                                OsAbi.ICMP_DEST_UNREACH -> "dest_unreachable"
+                                else -> "type_${hop.icmpType}"
+                            },
+                        ))))
+                        if (hop.icmpType == OsAbi.ICMP_DEST_UNREACH) reachedTarget = true
+                    }
+                }
+                if (reachedTarget) break
+            }
+
+            // dst_port varies per TTL (classic traceroute, and what was validated on hardware),
+            // so this flow is explicitly NOT fixed-tuple; base_port is in params.
+            val evidence = TracerouteEvidence(
+                flow = Flow(srcPort = srcPort, dstPort = BASE_PORT, fixedTuple = false),
+                hops = hops,
+            ).toEvidence()
+            val metrics = buildJsonObject {
+                put("hops_seen", hopsSeen)
+                put("reached_target", reachedTarget)
+            }
+            val status = when {
+                hopsSeen > 0 -> TestStatus.OK
+                // API present, sends succeeded, nothing surfaced: a fact about this path or
+                // kernel, not proof the mechanism is missing.
+                else -> TestStatus.PARTIAL
+            }
+            b.build(status, params = params, evidence = evidence, metrics = metrics)
+        } catch (e: Throwable) {
+            b.build(
+                TestStatus.FAILED,
+                params = params,
+                error = TestError("uncaught", e.message ?: e.javaClass.simpleName),
+            )
+        } finally {
+            fd?.let { runCatching { Os.close(it) } }
+        }
+    }
+}
+
+/**
+ * Reflection facade over android.system.{StructMsghdr, StructCmsghdr, Os.recvmsg}.
+ * Resolved once; null if any piece is missing on this API level.
+ */
+internal class ErrqueueApi private constructor(
+    private val msghdrCtor: java.lang.reflect.Constructor<*>,
+    private val recvmsg: java.lang.reflect.Method,
+    private val cmsgLevel: java.lang.reflect.Field,
+    private val cmsgType: java.lang.reflect.Field,
+    private val cmsgData: java.lang.reflect.Field,
+    private val msgControl: java.lang.reflect.Field,
+) {
+    class ErrEvent(
+        val offender: String?,
+        val icmpType: Int,
+        val origin: Int,
+        val parseError: String? = null,
+    )
+
+    /** One non-blocking MSG_ERRQUEUE read; null when the queue is empty. */
+    fun pollErrqueue(fd: FileDescriptor): ErrEvent? {
+        return try {
+            val iov = arrayOf(ByteBuffer.allocate(512))
+            // (SocketAddress msg_name, ByteBuffer[] msg_iov, StructCmsghdr[] msg_control, flags)
+            val msghdr = msghdrCtor.newInstance(
+                InetSocketAddress(0), iov, null, 0,
+            )
+            recvmsg.invoke(null, fd, msghdr, OsAbi.MSG_ERRQUEUE or OsAbi.MSG_DONTWAIT)
+            val control = msgControl.get(msghdr) as? Array<*>
+                ?: return ErrEvent(null, -1, -1, "msg_control empty after recvmsg")
+            for (cmsg in control.filterNotNull()) {
+                val level = cmsgLevel.getInt(cmsg)
+                val type = cmsgType.getInt(cmsg)
+                if (level == OsConstants.IPPROTO_IP && type == OsAbi.IP_RECVERR) {
+                    return parseSockExtendedErr(cmsgData.get(cmsg))
+                }
+            }
+            ErrEvent(null, -1, -1, "no IP_RECVERR cmsg among ${control.size}")
+        } catch (e: Throwable) {
+            // The single most load-bearing line: reflection wraps errno in
+            // InvocationTargetException, and EAGAIN there means "queue empty", not failure.
+            val cause = (e as? java.lang.reflect.InvocationTargetException)?.cause ?: e
+            val msg = cause.message ?: cause.javaClass.simpleName
+            if ("EAGAIN" in msg || "EWOULDBLOCK" in msg) null
+            else ErrEvent(null, -1, -1, msg)
+        }
+    }
+
+    /** cmsg_data = struct sock_extended_err + offender sockaddr_in (see OsAbi). */
+    private fun parseSockExtendedErr(data: Any?): ErrEvent {
+        val bytes: ByteArray = when (data) {
+            is ByteArray -> data
+            is ByteBuffer -> ByteArray(data.remaining()).also { data.duplicate().get(it) }
+            else -> return ErrEvent(null, -1, -1, "cmsg_data is ${data?.javaClass?.name}")
+        }
+        if (bytes.size < OsAbi.SOCK_EE_SIZE) {
+            return ErrEvent(null, -1, -1, "cmsg_data too short: ${bytes.size}")
+        }
+        val origin = bytes[4].toInt() and 0xFF
+        val icmpType = bytes[5].toInt() and 0xFF
+        // SO_EE_OFFENDER: sockaddr_in directly after the fixed struct; family is in native
+        // byte order, sin_addr at offset +4 within the sockaddr.
+        val offender = if (bytes.size >= OsAbi.SOCK_EE_SIZE + 8) {
+            val family = ByteBuffer.wrap(bytes, OsAbi.SOCK_EE_SIZE, 2)
+                .order(ByteOrder.nativeOrder()).short.toInt()
+            if (family == OsConstants.AF_INET) {
+                val a = bytes.copyOfRange(OsAbi.SOCK_EE_SIZE + 4, OsAbi.SOCK_EE_SIZE + 8)
+                InetAddress.getByAddress(a).hostAddress
+            } else null
+        } else null
+        return ErrEvent(offender, icmpType, origin)
+    }
+
+    companion object {
+        fun resolve(): ErrqueueApi? = runCatching {
+            val msghdrCls = Class.forName("android.system.StructMsghdr")
+            val cmsghdrCls = Class.forName("android.system.StructCmsghdr")
+            ErrqueueApi(
+                // Picked by shape, not by position: the 4-arg form is
+                // (SocketAddress, ByteBuffer[], StructCmsghdr[], int) on every level that has it.
+                msghdrCtor = msghdrCls.constructors.first { it.parameterCount == 4 },
+                recvmsg = Os::class.java.getMethod(
+                    "recvmsg", FileDescriptor::class.java, msghdrCls, Int::class.javaPrimitiveType,
+                ),
+                cmsgLevel = cmsghdrCls.getField("cmsg_level"),
+                cmsgType = cmsghdrCls.getField("cmsg_type"),
+                cmsgData = cmsghdrCls.getField("cmsg_data"),
+                msgControl = msghdrCls.getField("msg_control"),
+            )
+        }.getOrNull()
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/V6ConnectProbe.kt

@@ -0,0 +1,131 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import app.echo_lot.measurement.Network as MNetwork
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import java.net.Inet6Address
+import java.net.InetSocketAddress
+import java.util.Locale
+
+/**
+ * v6.brokenness — does IPv6 actually carry traffic, asked with a real TCP connection.
+ *
+ * This exists to corroborate (or refute) the ICMPv6 silence that icmp.ping6 observes. ICMPv6 echo
+ * is widely filtered on networks where IPv6 works fine, so silence alone cannot distinguish
+ * "IPv6 is broken" from "ping is filtered" — a phone that reported v6.broken while happily
+ * loading IPv6-only sites is what proved the point. A TCP connect over IPv6 to the configured
+ * server settles it: if it succeeds, IPv6 works and the ICMP silence is filtering; if it fails
+ * too, on a network that advertises IPv6, the brokenness claim finally has evidence behind it.
+ *
+ * Only networks that claim to offer IPv6 (a global address or a v6 default route) are attempted:
+ * connecting over v6 on an IPv4-only network fails by design, and recording that as evidence
+ * would manufacture the exact false positive this probe exists to kill.
+ */
+class V6ConnectProbe(
+    private val entries: List<NetworkInventory.Entry>,
+    private val serverHost: String,
+    private val port: Int = 443,
+) : Probe {
+    override val type = TestType.V6_BROKENNESS
+    override val tier = Tier.APP
+    // One 3s connect timeout per v6-provisioned network, at most.
+    override val estimatedMs = 4_000L
+
+    override suspend fun run(ctx: Context, ids: ProbeIds): Test = withContext(Dispatchers.IO) {
+        val b = TestBuilder(type, tier, ids)
+        // Same rule as the STUN and canary probes: with no server there is no target, and
+        // borrowing someone else's infrastructure to get one is not this app's call to make.
+        if (serverHost.isBlank()) {
+            return@withContext b.build(
+                TestStatus.SKIPPED,
+                evidence = buildJsonObject { put("reason", "no server configured to connect to") },
+            )
+        }
+        val candidates = entries.filter { ipv6Provisioned(it.model) }
+        if (candidates.isEmpty()) {
+            return@withContext b.build(
+                TestStatus.SKIPPED,
+                evidence = buildJsonObject {
+                    put("reason", "no active network claims to offer IPv6")
+                },
+            )
+        }
+
+        var okCount = 0
+        var attemptedCount = 0
+        val evidence: JsonObject = buildJsonObject {
+            put("target", "$serverHost:$port")
+            for (e in candidates) {
+                val label = "${e.model.transport.name.lowercase()}:${e.model.id}"
+                val a = attempt(e)
+                if (a.attempted) attemptedCount++
+                if (a.ok) okCount++
+                put(label, buildJsonObject {
+                    put("network_ref", e.model.id)
+                    put("ok", a.ok)
+                    put("attempted", a.attempted)
+                    put("detail", a.detail)
+                })
+            }
+        }
+        val status = when {
+            attemptedCount == 0 -> TestStatus.SKIPPED // resolution/binding never got that far
+            okCount == attemptedCount -> TestStatus.OK
+            okCount > 0 -> TestStatus.PARTIAL
+            else -> TestStatus.FAILED
+        }
+        b.build(status, evidence = evidence)
+    }
+
+    /** Same attempted/ok separation as IcmpProbe: a connect we never sent proves nothing. */
+    private data class Attempt(val ok: Boolean, val attempted: Boolean, val detail: String)
+
+    private fun attempt(e: NetworkInventory.Entry): Attempt {
+        // Resolved through this network's own resolver; a v6 address obtained over another
+        // network would still be connected to over this one, which is what matters.
+        val addr = runCatching {
+            e.handle.getAllByName(serverHost).filterIsInstance<Inet6Address>().firstOrNull()
+        }.getOrNull()
+            ?: return Attempt(false, false, "no AAAA answer for $serverHost via this network")
+
+        // createSocket() binds to the network at creation; failing here means the app could not
+        // use the interface at all (e.g. EPERM under a VPN) — nothing was sent, nothing is known.
+        val socket = try {
+            e.handle.socketFactory.createSocket()
+        } catch (t: Throwable) {
+            return Attempt(false, false, "socket unavailable: ${t.message ?: t.javaClass.simpleName}")
+        }
+        return try {
+            val t0 = System.nanoTime()
+            socket.connect(InetSocketAddress(addr, port), 3000)
+            val rttMs = (System.nanoTime() - t0) / 1_000_000.0
+            Attempt(true, true, "connected to [${addr.hostAddress}]:$port " +
+                "rtt_ms=${"%.1f".format(Locale.ROOT, rttMs)}")
+        } catch (t: Throwable) {
+            // A refused connection would still prove the path forwards IPv6, but against our own
+            // server's 443 the realistic failures are timeout and unreachable — both silence.
+            Attempt(false, true, "error: ${t.message ?: t.javaClass.simpleName}")
+        } finally {
+            runCatching { socket.close() }
+        }
+    }
+
+    /** The network claims IPv6: a global (non-link-local) address or a v6 default route. */
+    private fun ipv6Provisioned(n: MNetwork): Boolean =
+        n.link.addresses.any { a ->
+            a.addr.contains(':') &&
+                !a.addr.startsWith("fe80", ignoreCase = true) &&
+                !a.addr.startsWith("::1")
+        } || n.link.routes.any { it.dst == "::/0" }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/WifiSignalCollector.kt

@@ -0,0 +1,165 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import android.net.wifi.WifiManager
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import app.echo_lot.measurement.Transport
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.isActive
+import kotlinx.coroutines.launch
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import kotlinx.serialization.json.putJsonArray
+import kotlinx.serialization.json.add
+import java.util.Collections
+
+/**
+ * wifi.signal_log — RSSI, link speed and frequency sampled across the whole window.
+ *
+ * One reading of the signal strength says almost nothing: -67 dBm is fine, and -67 dBm that was
+ * -45 dBm ninety seconds ago is somebody walking away from the AP, or an AP whose power is being
+ * managed, or a band steer about to happen. The series is the measurement; the snapshot in
+ * `networks[].wifi` is only its first sample.
+ *
+ * Evidence is columnar (measurement-schema §6.2 conventions): parallel arrays keep a five-minute
+ * log at 2 s intervals in a few kB.
+ */
+class WifiSignalCollector(
+    private val entries: List<NetworkInventory.Entry>,
+    private val intervalMs: Long = 2_000,
+) : BaseCollector() {
+
+    override val type = TestType.WIFI_SIGNAL_LOG
+    override val tier = Tier.APP
+
+    private val atMonoNs: MutableList<Long> = Collections.synchronizedList(mutableListOf())
+    private val rssi: MutableList<Int> = Collections.synchronizedList(mutableListOf())
+    private val speed: MutableList<Int> = Collections.synchronizedList(mutableListOf())
+    private val freq: MutableList<Int> = Collections.synchronizedList(mutableListOf())
+    /** Only the count of distinct BSSIDs leaves this class — a roam is the fact worth reporting,
+     *  and the addresses themselves are neighbours' hardware identifiers. */
+    private val bssids = Collections.synchronizedSet(HashSet<String>())
+
+    private var scope: CoroutineScope? = null
+    private var unsupported: String? = null
+    private var startedAtMonoNs = 0L
+
+    override suspend fun start(ctx: Context, ids: ProbeIds) {
+        // network_ref up front: this samples the wifi link, and a signal log with nothing to
+        // attach it to is a series of numbers about an unnamed thing.
+        val wifiNet = entries.firstOrNull { it.model.transport == Transport.WIFI }
+        begin(ids, networkRef = wifiNet?.model?.id)
+        startedAtMonoNs = ids.monoNs()
+
+        val wifi = ctx.applicationContext.getSystemService(WifiManager::class.java)
+        if (wifi == null) {
+            unsupported = "WifiManager unavailable"
+            return
+        }
+        if (wifiNet == null) {
+            unsupported = "no wifi network is connected"
+            return
+        }
+        // Own scope, not the caller's: the run job is cancelled the instant the user taps Cancel,
+        // and the samples taken up to that point are exactly what a cancelled long run still owes
+        // them. stop() ends this scope.
+        val s = CoroutineScope(SupervisorJob() + Dispatchers.IO).also { scope = it }
+        s.launch {
+            while (isActive) {
+                sample(ids, wifi)
+                delay(intervalMs)
+            }
+        }
+    }
+
+    @Suppress("DEPRECATION")
+    private fun sample(ids: ProbeIds, wifi: WifiManager) {
+        // WifiManager.getConnectionInfo is deprecated in favour of the NetworkCallback's
+        // TransportInfo, which delivers a WifiInfo only when the capabilities change — i.e. at the
+        // platform's cadence, not ours, and with no way to ask for a sample. For a fixed-interval
+        // log the deprecated call is the one that answers the question, and it still works.
+        val info = runCatching { wifi.connectionInfo }.getOrNull() ?: return
+        val r = info.rssi
+        // -127 and 0 are the "no reading" sentinels; recording them would drag every average down
+        // and invent a signal cliff that never happened.
+        if (r == 0 || r <= -127) return
+        atMonoNs.add(ids.monoNs())
+        rssi.add(r)
+        speed.add(info.linkSpeed)
+        freq.add(runCatching { info.frequency }.getOrDefault(0))
+        runCatching { info.bssid }.getOrNull()
+            ?.takeIf { it.isNotBlank() && it != "02:00:00:00:00:00" }
+            ?.let { bssids.add(it) }
+    }
+
+    override suspend fun stop(): Test {
+        scope?.coroutineContext?.get(Job)?.cancel()
+        scope = null
+
+        unsupported?.let {
+            return build(
+                TestStatus.UNSUPPORTED,
+                params = params(),
+                error = TestError("no_wifi", it),
+            )
+        }
+
+        val t = synchronized(atMonoNs) { atMonoNs.toList() }
+        val r = synchronized(rssi) { rssi.toList() }
+        val sp = synchronized(speed) { speed.toList() }
+        val f = synchronized(freq) { freq.toList() }
+
+        val evidence: JsonObject = buildJsonObject {
+            putJsonArray("at_mono_ns") { for (v in t) add(v) }
+            putJsonArray("rssi_dbm") { for (v in r) add(v) }
+            putJsonArray("link_speed_mbps") { for (v in sp) add(v) }
+            putJsonArray("frequency_mhz") { for (v in f) add(v) }
+        }
+        val metrics: JsonObject = buildJsonObject {
+            put("samples", r.size)
+            if (r.isNotEmpty()) {
+                put("rssi_dbm_min", r.min())
+                put("rssi_dbm_avg", round1(r.average()))
+                put("rssi_dbm_max", r.max())
+                put("rssi_dbm_range", r.max() - r.min())
+            }
+            sp.filter { it > 0 }.let { valid ->
+                if (valid.isNotEmpty()) {
+                    put("link_speed_mbps_min", valid.min())
+                    put("link_speed_mbps_avg", round1(valid.average()))
+                    put("link_speed_mbps_max", valid.max())
+                }
+            }
+            // Distinct BSSIDs minus the one we started on: how often the phone changed AP without
+            // the network ever going down — invisible to any one-shot probe, and a common cause of
+            // "the call drops when I walk into the kitchen".
+            put("roams", (bssids.size - 1).coerceAtLeast(0))
+        }
+        return build(
+            if (r.isEmpty()) TestStatus.PARTIAL else TestStatus.OK,
+            evidence = evidence, metrics = metrics, params = params(),
+        )
+    }
+
+    private fun params(): JsonObject = buildJsonObject {
+        put("interval_ms", intervalMs)
+        put("started_mono_ns", startedAtMonoNs)
+        put("source", "WifiManager.connectionInfo")
+    }
+
+    private companion object {
+        fun round1(v: Double) = Math.round(v * 10.0) / 10.0
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/WsdCollector.kt

@@ -0,0 +1,133 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+
+/**
+ * local.wsd_inventory — WS-Discovery (SOAP-over-UDP, 3702) Hello / Bye / Probe / ProbeMatches.
+ *
+ * This is the protocol Windows and modern printers use to find each other, and it inventories a
+ * class of device the other three miss: network printers, scanners and IP cameras announce here and
+ * frequently nowhere else. A `Hello` is a device arriving, a `Bye` is one leaving, and a `Probe`
+ * from a workstation names what it is hunting for — so a window over 3702 shows both the equipment
+ * on the segment and which machines are looking for it.
+ *
+ * Passive only. WS-Discovery's active half is a Probe multicast, which would make this app a
+ * participant announcing itself to every device on the segment; SSDP's M-SEARCH is a single small
+ * request that devices expect constantly, whereas a WSD Probe from an unknown host is the kind of
+ * thing that shows up in someone's security log. Listening costs the network nothing.
+ *
+ * Payloads are decoded by [WsdParser], which does targeted extraction rather than XML parsing —
+ * see its documentation for why that is the right call for unauthenticated broadcast input.
+ */
+class WsdCollector : BaseCollector() {
+
+    override val type = TestType.LOCAL_WSD_INVENTORY
+    override val tier = Tier.APP
+
+    private val capture = MulticastCapture(
+        label = "wsd",
+        port = PORT,
+        group4 = GROUP4,
+        group6 = GROUP6,
+        // SOAP envelopes are an order of magnitude larger than the other three protocols'
+        // datagrams, so the byte ceiling binds before the packet count does. Both are set
+        // explicitly rather than left to the default, which was chosen for 200-byte packets.
+        maxPackets = 250,
+        maxBytesRetained = 192 * 1024,
+    )
+
+    private var startedAtMonoNs = 0L
+
+    override suspend fun start(ctx: Context, ids: ProbeIds) {
+        begin(ids)
+        startedAtMonoNs = ids.monoNs()
+        capture.acquireLock(ctx)
+        capture.start(ids)
+    }
+
+    override suspend fun stop(): Test {
+        val packets = capture.stop()
+
+        val table = DiscoveryTable()
+        var hello = 0
+        var bye = 0
+        var probes = 0
+        var matches = 0
+        var undecodable = 0
+
+        for (p in packets) {
+            val m = WsdParser.parse(p.data, p.data.size)
+            if (m == null) {
+                undecodable++
+                continue
+            }
+            when (m.action?.lowercase()) {
+                "hello" -> hello++
+                "bye" -> bye++
+                "probe" -> probes++
+                "probematches", "resolvematches" -> matches++
+            }
+            // The device UUID is WS-Discovery's own stable identity and survives address changes,
+            // so it is the identity where present; a Probe carries none (it names what it wants,
+            // not who it is), and there the action plus the types is what distinguishes one
+            // observation from a repeat of it.
+            val identity = m.deviceUuid ?: (m.action.orEmpty() + "/" + m.types.orEmpty())
+            table.observe(p.sourceIp, identity.ifEmpty { "(unidentified)" }, p.atMonoNs) {
+                buildJsonObject {
+                    m.deviceUuid?.let { put("device_uuid", it) }
+                    m.action?.let { put("action", it) }
+                    m.types?.let { put("wsd_types", it) }
+                    m.xaddrs?.let { put("wsd_xaddrs", it) }
+                }
+            }
+        }
+
+        val evidence: JsonObject = buildJsonObject {
+            put("capture", capture.statusJson())
+            put("wsd_devices", table.toJson())
+            put("evidence_truncated", capture.truncated || table.overflowed)
+        }
+        val metrics: JsonObject = buildJsonObject {
+            put("distinct_sources", table.distinctSources)
+            put("distinct_devices", table.size)
+            put("packets", capture.packetsSeen)
+            put("hello", hello)
+            put("bye", bye)
+            put("probes", probes)
+            put("probe_matches", matches)
+            put("undecodable_packets", undecodable)
+            put("truncated", capture.truncated || table.overflowed)
+        }
+        val saw = !table.isEmpty
+        return build(
+            capture.outcome(saw),
+            evidence = evidence,
+            metrics = metrics,
+            params = params(),
+            error = capture.reason(saw)?.let { TestError("listen_incomplete", it) },
+        )
+    }
+
+    private fun params(): JsonObject = buildJsonObject {
+        put("mode", "passive")
+        put("group_v4", "$GROUP4:$PORT")
+        put("group_v6", "[$GROUP6]:$PORT")
+        put("started_mono_ns", startedAtMonoNs)
+    }
+
+    private companion object {
+        const val PORT = 3702
+        const val GROUP4 = "239.255.255.250"
+        const val GROUP6 = "ff02::c"
+    }
+}

echolot-app/core-probe/src/test/kotlin/app/echo_lot/probe/DiscoveryParsersTest.kt

@@ -0,0 +1,386 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertNotNull
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+/**
+ * The decoders in DiscoveryParsers.kt, against payloads shaped like the ones real devices emit and
+ * against the ones a broken or hostile device emits.
+ *
+ * The malformed cases are the point. These four decoders are the only place in the app where bytes
+ * from an unidentified third party on the local segment are interpreted; they run inside a
+ * collector whose contract is that it never throws, and every one of them is reachable by anyone
+ * who can put a frame on the wire. So each protocol is fed truncation, junk, and the specific abuse
+ * its format invites — a DNS compression pointer, a NetBIOS name outside the A-P alphabet, an XML
+ * entity bomb — and the assertion is always the same pair: no exception, and no invented data.
+ */
+class DiscoveryParsersTest {
+
+    private fun bytes(s: String) = s.toByteArray(Charsets.ISO_8859_1)
+
+    // ---- SSDP --------------------------------------------------------------------------------
+
+    private val notifyAlive = bytes(
+        "NOTIFY * HTTP/1.1\r\n" +
+            "HOST: 239.255.255.250:1900\r\n" +
+            "CACHE-CONTROL: max-age=1800\r\n" +
+            "LOCATION: http://192.168.1.44:8060/\r\n" +
+            "NT: upnp:rootdevice\r\n" +
+            "NTS: ssdp:alive\r\n" +
+            "SERVER: Roku/12.5.5 UPnP/1.0 Roku/12.5.5\r\n" +
+            "USN: uuid:roku:ecp:YH00E1234567::upnp:rootdevice\r\n\r\n"
+    )
+
+    private val searchResponse = bytes(
+        "HTTP/1.1 200 OK\r\n" +
+            "CACHE-CONTROL: max-age=1800\r\n" +
+            "EXT:\r\n" +
+            "LOCATION: http://192.168.1.1:49000/rootDesc.xml\r\n" +
+            "SERVER: FRITZ!Box 7590 UPnP/1.0 AVM FRITZ!Box 7590 154.07.57\r\n" +
+            "ST: upnp:rootdevice\r\n" +
+            "USN: uuid:75802409-bccb-40e7-8e6c-c0ff33445566::upnp:rootdevice\r\n\r\n"
+    )
+
+    @Test
+    fun ssdpAliveAnnouncementYieldsIdentityAndLocation() {
+        val m = assertNotNull(SsdpParser.parse(notifyAlive, notifyAlive.size))
+        assertEquals(SsdpKind.ALIVE, m.kind)
+        assertEquals("upnp:rootdevice", m.target)
+        assertEquals("uuid:roku:ecp:YH00E1234567::upnp:rootdevice", m.usn)
+        assertEquals("http://192.168.1.44:8060/", m.location)
+        assertEquals("Roku/12.5.5 UPnP/1.0 Roku/12.5.5", m.serverBanner)
+    }
+
+    @Test
+    fun ssdpByebyeIsDistinguishedFromAlive() {
+        val byebye = bytes(
+            "NOTIFY * HTTP/1.1\r\nHOST: 239.255.255.250:1900\r\n" +
+                "NT: urn:schemas-upnp-org:device:MediaRenderer:1\r\nNTS: ssdp:byebye\r\n" +
+                "USN: uuid:aabbccdd::urn:schemas-upnp-org:device:MediaRenderer:1\r\n\r\n"
+        )
+        val m = assertNotNull(SsdpParser.parse(byebye, byebye.size))
+        assertEquals(SsdpKind.BYEBYE, m.kind)
+        assertEquals("urn:schemas-upnp-org:device:MediaRenderer:1", m.target)
+        assertNull(m.location)
+    }
+
+    @Test
+    fun ssdpSearchResponseReadsStAsTheTarget() {
+        val m = assertNotNull(SsdpParser.parse(searchResponse, searchResponse.size))
+        assertEquals(SsdpKind.RESPONSE, m.kind)
+        assertEquals("upnp:rootdevice", m.target)
+        assertEquals("http://192.168.1.1:49000/rootDesc.xml", m.location)
+    }
+
+    /** Our own M-SEARCH comes back through the group; it must be recognisable so the collector
+     *  does not inventory the phone doing the measuring. */
+    @Test
+    fun ssdpOwnSearchIsRecognisable() {
+        val search = bytes(
+            "M-SEARCH * HTTP/1.1\r\nHOST: 239.255.255.250:1900\r\n" +
+                "MAN: \"ssdp:discover\"\r\nMX: 3\r\nST: upnp:rootdevice\r\n\r\n"
+        )
+        assertEquals(SsdpKind.SEARCH, assertNotNull(SsdpParser.parse(search, search.size)).kind)
+    }
+
+    @Test
+    fun ssdpProductHintDropsBoilerplateAndKeepsTheModel() {
+        assertEquals("Roku/12.5.5", SsdpParser.productHint("Roku/12.5.5 UPnP/1.0 Roku/12.5.5"))
+        assertEquals("Synology/DSM-7.3", SsdpParser.productHint("Linux/4.4 UPnP/1.0 Synology/DSM-7.3"))
+        val fritz = assertNotNull(SsdpParser.productHint("FRITZ!Box 7590 UPnP/1.0 AVM FRITZ!Box 7590"))
+        assertTrue(fritz.contains("FRITZ!Box"))
+        assertFalse(fritz.contains("UPnP"), "protocol boilerplate leaked into the model hint")
+        assertNull(SsdpParser.productHint(null))
+        assertNull(SsdpParser.productHint("   "))
+        // A banner that is nothing but boilerplate reveals no model and must say so, rather than
+        // returning an empty string that reads as a name nobody could see.
+        assertNull(SsdpParser.productHint("Linux/4.4 UPnP/1.0"))
+    }
+
+    @Test
+    fun ssdpMalformedIsRejectedWithoutThrowing() {
+        // Truncated mid-header: the headers that did arrive are still usable, and the missing NTS
+        // makes the kind unknown rather than making the packet a lie.
+        val cut = notifyAlive.copyOf(70)
+        assertEquals(SsdpKind.OTHER, assertNotNull(SsdpParser.parse(cut, cut.size)).kind)
+
+        assertNull(SsdpParser.parse(ByteArray(0), 0))
+        val blank = bytes("\r\n\r\n")
+        assertNull(SsdpParser.parse(blank, blank.size))
+        val http = bytes("GET / HTTP/1.0\r\n\r\n")
+        assertNull(SsdpParser.parse(http, http.size), "not an SSDP verb")
+        // Arbitrary binary, including the high bytes ISO-8859-1 must not choke on.
+        val junk = ByteArray(256) { it.toByte() }
+        assertNull(SsdpParser.parse(junk, junk.size))
+        // A declared length longer than the buffer must be refused, not read past.
+        assertNull(SsdpParser.parse(notifyAlive, notifyAlive.size + 100))
+        // Header lines with no colon are skipped rather than fatal.
+        val noColon = bytes("NOTIFY * HTTP/1.1\r\ngarbage line\r\nNTS: ssdp:alive\r\n\r\n")
+        assertEquals(SsdpKind.ALIVE, assertNotNull(SsdpParser.parse(noColon, noColon.size)).kind)
+    }
+
+    // ---- LLMNR -------------------------------------------------------------------------------
+
+    /** Builds a DNS-format packet: header, one question, nothing else. */
+    private fun dnsQuery(
+        name: String,
+        qtype: Int = 1,
+        id: Int = 0x1234,
+        flags: Int = 0x0000,
+        qdcount: Int = 1,
+    ): ByteArray {
+        val out = ArrayList<Byte>()
+        fun u16(v: Int) { out.add((v shr 8).toByte()); out.add((v and 0xFF).toByte()) }
+        u16(id); u16(flags); u16(qdcount); u16(0); u16(0); u16(0)
+        for (label in name.split('.')) {
+            val b = label.toByteArray(Charsets.UTF_8)
+            out.add(b.size.toByte())
+            b.forEach { out.add(it) }
+        }
+        out.add(0)
+        u16(qtype); u16(1)
+        return out.toByteArray()
+    }
+
+    @Test
+    fun llmnrQueryYieldsTheNameAWorkstationIsHuntingFor() {
+        val p = dnsQuery("wpad")
+        val q = assertNotNull(LlmnrParser.parse(p, p.size))
+        assertEquals("wpad", q.name)
+        assertEquals(1, q.qtype)
+        assertEquals("A", LlmnrParser.qtypeName(q.qtype))
+        assertTrue(q.isQuery)
+        assertEquals(0, q.opcode)
+    }
+
+    @Test
+    fun llmnrMultiLabelNamesAndAaaaSurviveIntact() {
+        val p = dnsQuery("nas-backup.local", qtype = 28)
+        val q = assertNotNull(LlmnrParser.parse(p, p.size))
+        assertEquals("nas-backup.local", q.name)
+        assertEquals("AAAA", LlmnrParser.qtypeName(q.qtype))
+    }
+
+    @Test
+    fun llmnrResponsesAreSeparatedFromQueries() {
+        val p = dnsQuery("DESKTOP-A1B2C3", flags = 0x8000)
+        assertFalse(assertNotNull(LlmnrParser.parse(p, p.size)).isQuery)
+    }
+
+    @Test
+    fun llmnrMalformedIsRejectedWithoutThrowing() {
+        val good = dnsQuery("printer")
+
+        assertNull(LlmnrParser.parse(ByteArray(0), 0))
+        assertNull(LlmnrParser.parse(good, 8), "a header-length prefix is not a question")
+        assertNull(LlmnrParser.parse(good, good.size + 50), "declared length past the buffer")
+
+        val noQuestion = dnsQuery("x", qdcount = 0)
+        assertNull(LlmnrParser.parse(noQuestion, noQuestion.size))
+
+        // A label length that runs off the end of the datagram — the classic truncation.
+        val overrun = good.copyOf(good.size - 6)
+        assertNull(LlmnrParser.parse(overrun, overrun.size))
+
+        // A compression pointer: legal DNS, forbidden in LLMNR, and the shape that makes a naive
+        // decoder loop forever. It must be refused rather than followed.
+        val pointer = good.copyOf(20)
+        pointer[12] = 0xC0.toByte()
+        pointer[13] = 0x0C
+        assertNull(LlmnrParser.parse(pointer, pointer.size))
+
+        // Random bytes behind a plausible header: whatever comes back, it is not an exception.
+        val junk = ByteArray(64) { (it * 37).toByte() }
+        junk[4] = 0; junk[5] = 1
+        LlmnrParser.parse(junk, junk.size)
+    }
+
+    // ---- NetBIOS -----------------------------------------------------------------------------
+
+    /** First-level encoding, the same transform the decoder has to undo. */
+    private fun nbnsPacket(name: String, suffix: Int, flags: Int = 0x2810): ByteArray {
+        val raw = ByteArray(16) { ' '.code.toByte() }
+        name.forEachIndexed { i, c -> if (i < 15) raw[i] = c.code.toByte() }
+        raw[15] = suffix.toByte()
+
+        val out = ArrayList<Byte>()
+        fun u16(v: Int) { out.add((v shr 8).toByte()); out.add((v and 0xFF).toByte()) }
+        u16(0x8001); u16(flags); u16(1); u16(0); u16(0); u16(1)
+        out.add(32)
+        for (b in raw) {
+            val v = b.toInt() and 0xFF
+            out.add(('A'.code + (v shr 4)).toByte())
+            out.add(('A'.code + (v and 0x0F)).toByte())
+        }
+        out.add(0)
+        u16(0x0020); u16(0x0001)
+        return out.toByteArray()
+    }
+
+    @Test
+    fun netbiosNameDecodesWithItsSuffixAndRole() {
+        val p = nbnsPacket("DESKTOP-A1B2C3", 0x20)
+        val n = assertNotNull(NetbiosParser.parse(p, p.size))
+        assertEquals("DESKTOP-A1B2C3", n.name)
+        assertEquals(0x20, n.suffix)
+        assertEquals("file_server", n.role)
+        assertFalse(n.isResponse)
+        assertEquals("registration", NetbiosParser.opcodeName(n.opcode))
+    }
+
+    @Test
+    fun netbiosPaddingIsStrippedAndSuffixesAreNamed() {
+        val p = nbnsPacket("WORKGROUP", 0x1E)
+        val n = assertNotNull(NetbiosParser.parse(p, p.size))
+        assertEquals("WORKGROUP", n.name, "the 15-byte space padding leaked into the name")
+        assertEquals("browser_elections", n.role)
+        assertEquals("workstation", NetbiosParser.roleOf(0x00))
+        assertEquals("suffix_0xAB", NetbiosParser.roleOf(0xAB))
+    }
+
+    @Test
+    fun netbiosResponsesAreSeparatedFromRequests() {
+        val p = nbnsPacket("FILESRV", 0x20, flags = 0x8500)
+        assertTrue(assertNotNull(NetbiosParser.parse(p, p.size)).isResponse)
+    }
+
+    @Test
+    fun netbiosMalformedIsRejectedWithoutThrowing() {
+        val good = nbnsPacket("PRINTER", 0x00)
+
+        assertNull(NetbiosParser.parse(ByteArray(0), 0))
+        assertNull(NetbiosParser.parse(good, 20), "truncated before the encoded name ends")
+        assertNull(NetbiosParser.parse(good, good.size + 40), "declared length past the buffer")
+
+        // A character outside A-P cannot be half of an encoded byte. Guessing at the rest would
+        // fabricate a hostname, so the whole packet is refused.
+        val badAlphabet = good.copyOf()
+        badAlphabet[15] = 'Z'.code.toByte()
+        assertNull(NetbiosParser.parse(badAlphabet, badAlphabet.size))
+
+        // The length byte must be exactly 32; anything else is a different protocol on this port.
+        val badLen = good.copyOf()
+        badLen[12] = 16
+        assertNull(NetbiosParser.parse(badLen, badLen.size))
+
+        // A name that decodes to nothing but padding is not a name.
+        val blank = nbnsPacket("", 0x00)
+        assertNull(NetbiosParser.parse(blank, blank.size))
+
+        val junk = ByteArray(80) { (it * 13).toByte() }
+        NetbiosParser.parse(junk, junk.size)
+    }
+
+    @Test
+    fun netbiosControlCharactersInANameAreNeutralised() {
+        // Legal first-level encoding, illegal content: these bytes decode cleanly and would
+        // otherwise reach a JSON document, and from there somebody's terminal.
+        val p = nbnsPacket("A\u0001B\u0002C", 0x00)
+        assertEquals("A?B?C", assertNotNull(NetbiosParser.parse(p, p.size)).name)
+    }
+
+    // ---- WS-Discovery ------------------------------------------------------------------------
+
+    private val wsdHello = bytes(
+        """<?xml version="1.0" encoding="utf-8"?>
+        <soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope"
+                       xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing"
+                       xmlns:wsd="http://schemas.xmlsoap.org/ws/2005/04/discovery"
+                       xmlns:wsdp="http://schemas.xmlsoap.org/ws/2006/02/devprof">
+          <soap:Header>
+            <wsa:To>urn:schemas-xmlsoap-org:ws:2005:04:discovery</wsa:To>
+            <wsa:Action>http://schemas.xmlsoap.org/ws/2005/04/discovery/Hello</wsa:Action>
+            <wsa:MessageID>urn:uuid:0a7e6d1b-0000-4000-8000-000000000001</wsa:MessageID>
+          </soap:Header>
+          <soap:Body>
+            <wsd:Hello>
+              <wsa:EndpointReference>
+                <wsa:Address>urn:uuid:9f8e7d6c-1111-4222-8333-444455556666</wsa:Address>
+              </wsa:EndpointReference>
+              <wsd:Types>wsdp:Device pub:Computer</wsd:Types>
+              <wsd:XAddrs>http://192.168.1.77:5357/8f2c-4b1a/</wsd:XAddrs>
+              <wsd:MetadataVersion>1</wsd:MetadataVersion>
+            </wsd:Hello>
+          </soap:Body>
+        </soap:Envelope>"""
+    )
+
+    @Test
+    fun wsdHelloYieldsActionUuidTypesAndXaddrs() {
+        val m = assertNotNull(WsdParser.parse(wsdHello, wsdHello.size))
+        assertEquals("Hello", m.action)
+        assertEquals(
+            "urn:uuid:9f8e7d6c-1111-4222-8333-444455556666", m.deviceUuid,
+            "the EndpointReference address is the device identity, not the header MessageID",
+        )
+        assertEquals("wsdp:Device pub:Computer", m.types)
+        assertEquals("http://192.168.1.77:5357/8f2c-4b1a/", m.xaddrs)
+    }
+
+    @Test
+    fun wsdProbeCarriesNoDeviceIdentityAndIsStillRecorded() {
+        val probe = bytes(
+            """<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope"
+                             xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing"
+                             xmlns:wsd="http://schemas.xmlsoap.org/ws/2005/04/discovery">
+              <soap:Header>
+                <wsa:Action>http://schemas.xmlsoap.org/ws/2005/04/discovery/Probe</wsa:Action>
+              </soap:Header>
+              <soap:Body><wsd:Probe><wsd:Types>wsdp:Device</wsd:Types></wsd:Probe></soap:Body>
+            </soap:Envelope>"""
+        )
+        val m = assertNotNull(WsdParser.parse(probe, probe.size))
+        assertEquals("Probe", m.action)
+        assertNull(m.deviceUuid)
+        assertEquals("wsdp:Device", m.types)
+    }
+
+    @Test
+    fun wsdMalformedIsRejectedWithoutThrowing() {
+        assertNull(WsdParser.parse(ByteArray(0), 0))
+        assertNull(WsdParser.parse(wsdHello, wsdHello.size + 100), "declared length past the buffer")
+        val prose = bytes("hello world")
+        assertNull(WsdParser.parse(prose, prose.size), "not a SOAP envelope")
+        // An envelope with no leaf worth reading is an absence, not an empty device.
+        val bare = bytes("<soap:Envelope></soap:Envelope>")
+        assertNull(WsdParser.parse(bare, bare.size))
+
+        // Cut mid-element: whatever was complete is extracted, the rest is simply absent.
+        val cut = wsdHello.copyOf(wsdHello.size / 2)
+        WsdParser.parse(cut, cut.size)?.let { assertNull(it.xaddrs, "an unterminated element was invented") }
+
+        val junk = ByteArray(512) { (it * 7).toByte() }
+        assertNull(WsdParser.parse(junk, junk.size))
+    }
+
+    @Test
+    fun wsdHostileXmlCostsNothingBecauseNothingParsesItAsXml() {
+        // A billion-laughs entity bomb. Against a real XML parser this expands to gigabytes; here
+        // the entities are never resolved, which is the entire reason for not using one.
+        val bomb = bytes(
+            "<!DOCTYPE lolz [<!ENTITY lol \"lol\">" +
+                (0..8).joinToString("") { i ->
+                    val prev = if (i == 0) "" else (i - 1).toString()
+                    "<!ENTITY lol$i \"&lol$prev;&lol$prev;\">"
+                } +
+                "]><soap:Envelope><wsa:Action>x/Bye</wsa:Action><body>&lol8;</body></soap:Envelope>"
+        )
+        assertEquals("Bye", assertNotNull(WsdParser.parse(bomb, bomb.size)).action)
+
+        // Nesting deep enough to blow a recursive-descent parser's stack.
+        val deep = bytes("<soap:Envelope>" + "<a>".repeat(20_000) + "</soap:Envelope>")
+        WsdParser.parse(deep, deep.size)
+
+        // A payload far larger than any real datagram, pinning that the text cap is applied before
+        // the matching rather than after it.
+        val huge = bytes("<soap:Envelope><wsa:Action>x/Hello</wsa:Action>" + "z".repeat(200_000))
+        assertEquals("Hello", assertNotNull(WsdParser.parse(huge, huge.size)).action)
+    }
+}

echolot-app/core-protocol/src/main/kotlin/app/echo_lot/protocol/ControlClient.kt

@@ -35,13 +35,57 @@ class ControlClient(
     private val controlUrl: String,
     pins: Set<String>,
     private val appVersion: String = "",
+    /**
+     * Addresses to fall back to when the server's name will not resolve, learned from its profile.
+     *
+     * A measurement tool that cannot report from a broken network is useless exactly when it
+     * matters, and a wedged resolver is one of the faults it is built to find — it should not also
+     * be the thing that stops the finding being delivered.
+     *
+     * Safe because the pin is the trust and the name is not part of it: the server presents the
+     * same certificate whether it was reached by name or by address, and a wrong address fails the
+     * pin like anything else would.
+     */
+    private val fallbackAddrs: List<String> = emptyList(),
 ) {
 
     private val json = Json { ignoreUnknownKeys = true }
     private val socketFactory = Pinning.sslContext(pins).socketFactory
 
+    /**
+     * The base URL to use, substituting a cached address only when the name genuinely fails.
+     *
+     * Resolved once per client and only on failure, so a working network pays nothing and never
+     * silently drifts onto an address that may be stale.
+     */
+    private val base: String by lazy { resolveBase() }
+
+    private fun resolveBase(): String {
+        if (fallbackAddrs.isEmpty()) return controlUrl
+        val uri = runCatching { java.net.URI(controlUrl) }.getOrNull() ?: return controlUrl
+        val host = uri.host ?: return controlUrl
+        if (runCatching { java.net.InetAddress.getByName(host) }.isSuccess) return controlUrl
+
+        val port = if (uri.port > 0) uri.port else 443
+        for (ip in fallbackAddrs) {
+            // Checked rather than assumed: on a v4-only network a v6 address would otherwise be
+            // chosen and fail slowly, which is the wrong answer delivered late.
+            val reachable = runCatching {
+                java.net.Socket().use { sock ->
+                    sock.connect(java.net.InetSocketAddress(ip, port), 4000)
+                    true
+                }
+            }.getOrDefault(false)
+            if (reachable) {
+                val literal = if (ip.contains(':')) "[$ip]" else ip
+                return uri.scheme + "://" + literal + ":" + port
+            }
+        }
+        return controlUrl
+    }
+
     private fun open(path: String, method: String, credential: String?): HttpsURLConnection {
-        val conn = URL(controlUrl.trimEnd('/') + path).openConnection() as HttpsURLConnection
+        val conn = URL(base.trimEnd('/') + path).openConnection() as HttpsURLConnection
         conn.sslSocketFactory = socketFactory
         conn.setHostnameVerifier { _, _ -> true } // pin is the trust, not the name
         conn.requestMethod = method
@@ -165,6 +209,36 @@ class ControlClient(
         }
     }
 
+    /**
+     * Reports where adbd's wireless-debug listener can be reached on this device's LAN.
+     *
+     * Dev scaffolding, not a measurement: it exists because mDNS does not cross subnets, so a
+     * developer working from a different network cannot discover the port that rotates every few
+     * minutes. A device sitting on the test LAN can see it and say so. Deliberately not part of
+     * the probe protocol's capability set — the server documents it as a dev relay.
+     */
+    fun reportAdbEndpoint(
+        credential: String,
+        host: String,
+        port: Int,
+        deviceName: String? = null,
+        note: String? = null,
+    ): String {
+        val conn = open("/v1/devtools/adb-endpoint", "POST", credential)
+        val fields = buildString {
+            append("""{"host":${jstr(host)},"port":$port""")
+            deviceName?.let { append(""","device_name":${jstr(it)}""") }
+            note?.let { append(""","note":${jstr(it)}""") }
+            append("}")
+        }
+        writeJson(conn, fields)
+        val body = body(conn)
+        check(conn.responseCode in 200..299) {
+            "adb endpoint report failed: ${conn.responseCode} $body"
+        }
+        return body
+    }
+
     /** Lists this device's runs stored on the server. */
     fun listRuns(credential: String): String {
         val conn = open("/v1/runs", "GET", credential)

echolot-app/core-protocol/src/main/kotlin/app/echo_lot/protocol/Enrollment.kt

@@ -45,11 +45,22 @@ data class EnrollmentLink(
      * the reason the pin travels in the link at all.
      */
     fun redeem(deviceName: String? = null, appVersion: String = ""): Enrolled {
-        val client = ControlClient(controlUrl, setOf(pin), appVersion)
+        // The link may name the server's public address rather than its control endpoint, so that
+        // a person is handed a name they recognise. Ask where to actually connect.
+        //
+        // Only the address comes from here. The pin still comes from the link, because a pin
+        // fetched over an ordinary TLS connection would be worth exactly what the certificate
+        // authorities are worth — and pinning exists to survive one the operator does not
+        // control, such as a root injected by corporate device management. An intercepted
+        // discovery can therefore send this device to the wrong host, where the pin will not
+        // match: an outage, not a compromise.
+        val endpoint = discover(controlUrl) ?: controlUrl
+        val client = ControlClient(endpoint, setOf(pin), appVersion)
         val response = client.enroll(token, deviceName)
         val profile = client.profile(response.credential)
         return Enrolled(
-            controlUrl = controlUrl,
+            controlUrl = endpoint,
+            publicUrl = controlUrl,
             pin = pin,
             credential = response.credential,
             deviceId = response.deviceId,
@@ -57,6 +68,29 @@ data class EnrollmentLink(
         )
     }
 
+    /**
+     * Asks a server where its control plane lives. Null when it does not say, or cannot be asked.
+     *
+     * Deliberately forgiving: a server that predates this, or one whose link already names the
+     * control endpoint directly, simply answers nothing and the link's own URL is used. Enrollment
+     * must not start failing because an optional lookup did.
+     */
+    private fun discover(publicUrl: String): String? = runCatching {
+        val conn = (java.net.URL(publicUrl.trimEnd('/') + "/v1/discover").openConnection()
+            as java.net.HttpURLConnection).apply {
+            connectTimeout = 8_000
+            readTimeout = 8_000
+            setRequestProperty("Accept", "application/json")
+        }
+        if (conn.responseCode !in 200..299) return null
+        val body = conn.inputStream.bufferedReader().use { it.readText() }
+        kotlinx.serialization.json.Json { ignoreUnknownKeys = true }
+            .parseToJsonElement(body)
+            .let { (it as kotlinx.serialization.json.JsonObject)["control_url"] }
+            ?.let { (it as kotlinx.serialization.json.JsonPrimitive).content }
+            ?.takeIf { it.isNotBlank() }
+    }.getOrNull()
+
     companion object {
         const val SCHEME = "echolot"
         const val HOST = "enroll"
@@ -111,7 +145,15 @@ data class EnrollmentLink(
 
 /** A server this device is now enrolled with, ready to be stored in settings. */
 data class Enrolled(
+    /** Where this device connects: the endpoint whose certificate the pin matches. */
     val controlUrl: String,
+    /**
+     * The address a person was given, kept for display.
+     *
+     * Shown instead of [controlUrl] because the endpoint is plumbing — it exists to select a
+     * certificate — while this is the name the operator handed out and would recognise.
+     */
+    val publicUrl: String,
     val pin: String,
     val credential: String,
     val deviceId: String,

echolot-app/core-protocol/src/main/kotlin/app/echo_lot/protocol/Model.kt

@@ -29,6 +29,15 @@ data class Target(
     val id: String,
     val ip4: String? = null,
     val ip6: String? = null,
+    /**
+     * The second address, which RFC 5780 behaviour discovery redirects to.
+     *
+     * Worth surfacing rather than treating as an implementation detail: a report that says "the
+     * server did not answer" means something different depending on which of its addresses was
+     * asked, and an operator reading one needs to be able to tell.
+     */
+    @SerialName("ip4_alt") val ip4Alt: String? = null,
+    @SerialName("ip6_alt") val ip6Alt: String? = null,
     @SerialName("udp_port") val udpPort: Int = 0,
     @SerialName("tcp_port") val tcpPort: Int = 0,
     @SerialName("stun_port") val stunPort: Int = 0,

echolot-app/core-protocol/src/main/kotlin/app/echo_lot/protocol/ProbeSession.kt

@@ -152,6 +152,149 @@ class ProbeSession(
     /** What one upstream run put on the wire locally. */
     data class Sent(val packets: Int, val bytes: Long, val durationMs: Long, val kbps: Int)
 
+    // ---- upstream trains (spec §3.2, types 0x03-0x05) --------------------------------------
+
+    /** One TRAIN_DATA packet as sent: its wire seq, local tx time and size. */
+    data class TrainPacket(val seq: Int, val tTxNs: Long, val sizeBytes: Int)
+
+    /** One row of the server's received view. 255 in ttl/dscp/ecn means "not observed". */
+    data class TrainRow(
+        val seq: Int, val tRxNs: Long, val sizeBytes: Int,
+        val ttl: Int, val dscp: Int, val ecn: Int,
+    )
+
+    /**
+     * The server's account of one train. [received] counts every packet that arrived, buffered
+     * or not; [truncated] mirrors the wire flag (rows beyond the server's cap were counted but
+     * not kept). [partsExpected]/[partsReceived] make a lossy report path visible instead of
+     * letting missing rows masquerade as train loss.
+     */
+    data class TrainReport(
+        val trainId: Int,
+        val received: Int,
+        val truncated: Boolean,
+        val rows: List<TrainRow>,
+        val partsExpected: Int,
+        val partsReceived: Int,
+    )
+
+    /**
+     * Sends one paced upstream train. Nothing comes back per packet by design; pair with
+     * [trainReport] to learn what arrived. The absolute schedule (not sleep-per-packet) is the
+     * same anti-drift choice as [sendThroughput].
+     */
+    fun sendTrain(trainId: Int, count: Int, sizeBytes: Int = 200, interPacketMs: Long = 5): List<TrainPacket> {
+        val size = sizeBytes.coerceIn(Wire.HEADER_SIZE + 4, 1472)
+        val out = ArrayList<TrainPacket>(count)
+        val start = System.nanoTime()
+        var next = start
+        for (i in 0 until count) {
+            val payload = ByteArray(size - Wire.HEADER_SIZE)
+            payload[0] = (trainId ushr 24).toByte(); payload[1] = (trainId ushr 16).toByte()
+            payload[2] = (trainId ushr 8).toByte(); payload[3] = trainId.toByte()
+            val tTx = nowNs()
+            val pkt = Wire.build(Wire.TYPE_TRAIN_DATA, prefix, ++seq, tTx, key, payload)
+            try {
+                socket.send(DatagramPacket(pkt, pkt.size, server))
+            } catch (e: java.io.IOException) {
+                // A local send failure is our condition, not the path's: report what actually
+                // left rather than letting the server's report read as loss.
+                break
+            }
+            out.add(TrainPacket(seq, tTx, pkt.size))
+            next += interPacketMs * 1_000_000
+            val sleepNs = next - System.nanoTime()
+            if (sleepNs > 0) Thread.sleep(sleepNs / 1_000_000, (sleepNs % 1_000_000).toInt())
+        }
+        return out
+    }
+
+    /**
+     * Fetches the server's received view of a train (one REPORT_REQ, N REPORT datagrams).
+     *
+     * Returns null when no report arrives at all — indistinguishable between "report lost" and
+     * "server predates trains", and the caller must say so rather than choose. Missing parts of
+     * a multi-part report are tolerated and visible via partsReceived < partsExpected.
+     */
+    fun trainReport(trainId: Int, timeoutMs: Long = 3_000): TrainReport? {
+        val req = ByteArray(4)
+        req[0] = (trainId ushr 24).toByte(); req[1] = (trainId ushr 16).toByte()
+        req[2] = (trainId ushr 8).toByte(); req[3] = trainId.toByte()
+        val pkt = Wire.build(Wire.TYPE_TRAIN_REPORT_REQ, prefix, ++seq, nowNs(), key, req)
+        socket.send(DatagramPacket(pkt, pkt.size, server))
+
+        var received = 0
+        var truncated = false
+        var partsExpected = -1
+        val seenParts = HashSet<Int>()
+        val rows = ArrayList<TrainRow>()
+        val deadline = System.nanoTime() + timeoutMs * 1_000_000
+        val buf = ByteArray(2048)
+        val prevTimeout = socket.soTimeout
+        try {
+            while (partsExpected < 0 || seenParts.size < partsExpected) {
+                val remainMs = ((deadline - System.nanoTime()) / 1_000_000).toInt()
+                if (remainMs <= 0) break
+                socket.soTimeout = remainMs.coerceAtMost(1000)
+                val dp = DatagramPacket(buf, buf.size)
+                try {
+                    socket.receive(dp)
+                } catch (e: java.net.SocketTimeoutException) {
+                    continue
+                }
+                val p = Wire.parseVerified(buf, dp.length, key) ?: continue
+                if (p.type != Wire.TYPE_TRAIN_REPORT) continue
+                val part = parseReportPart(p.payload, trainId) ?: continue
+                if (!seenParts.add(part.part)) continue
+                received = part.received
+                truncated = truncated || part.truncated
+                partsExpected = part.parts
+                rows.addAll(part.rows)
+            }
+        } finally {
+            socket.soTimeout = prevTimeout
+        }
+        if (seenParts.isEmpty()) return null
+        rows.sortBy { it.seq }
+        return TrainReport(trainId, received, truncated, rows, partsExpected, seenParts.size)
+    }
+
+    private class ReportPart(
+        val part: Int, val parts: Int, val received: Int,
+        val truncated: Boolean, val rows: List<TrainRow>,
+    )
+
+    /** Mirrors the server's columnar layout (dataplane/train.go buildTrainReport). */
+    private fun parseReportPart(b: ByteArray, wantId: Int): ReportPart? {
+        if (b.size < 16) return null
+        fun u16(off: Int) = ((b[off].toInt() and 0xFF) shl 8) or (b[off + 1].toInt() and 0xFF)
+        fun u32(off: Int) = ((b[off].toLong() and 0xFF) shl 24) or ((b[off + 1].toLong() and 0xFF) shl 16) or
+            ((b[off + 2].toLong() and 0xFF) shl 8) or (b[off + 3].toLong() and 0xFF)
+        if (u32(0).toInt() != wantId) return null
+        val received = u32(4).toInt()
+        val part = u16(8)
+        val parts = u16(10)
+        val truncated = (b[12].toInt() and 0x01) != 0
+        val n = u16(14)
+        if (b.size < 16 + n * 17) return null
+        val rows = ArrayList<TrainRow>(n)
+        var off = 16
+        val seqs = IntArray(n) { u32(off + it * 4).toInt() }; off += n * 4
+        val tRx = LongArray(n) {
+            var v = 0L
+            for (j in 0 until 8) v = (v shl 8) or (b[off + it * 8 + j].toLong() and 0xFF)
+            v
+        }; off += n * 8
+        val sizes = IntArray(n) { u16(off + it * 2) }; off += n * 2
+        val ttls = IntArray(n) { b[off + it].toInt() and 0xFF }; off += n
+        val dscps = IntArray(n) { b[off + it].toInt() and 0xFF }; off += n
+        val ecns = IntArray(n) { b[off + it].toInt() and 0xFF }
+        for (i in 0 until n) {
+            rows.add(TrainRow(seqs[i], tRx[i], sizes[i], ttls[i], dscps[i], ecns[i]))
+        }
+        return ReportPart(part, parts, received, truncated, rows)
+    }
+
     /** One packet received from the server, with the wire size actually delivered. */
     data class Received(val type: Int, val seq: Int, val sizeBytes: Int, val tRxNs: Long)
 

echolot-app/core-protocol/src/main/kotlin/app/echo_lot/protocol/Wire.kt

@@ -23,6 +23,14 @@ object Wire {
 
     const val TYPE_ECHO_REQ: Int = 0x01
     const val TYPE_ECHO_RESP: Int = 0x02
+    /**
+     * Upstream train (spec §3.2): DATA is deliberately unanswered — a per-packet reply would
+     * double the traffic and drag the return path into a measurement of the outbound one. The
+     * server's received view comes back afterwards via REPORT_REQ → one or more REPORTs.
+     */
+    const val TYPE_TRAIN_DATA: Int = 0x03
+    const val TYPE_TRAIN_REPORT_REQ: Int = 0x04
+    const val TYPE_TRAIN_REPORT: Int = 0x05
     const val TYPE_TIMESYNC_REQ: Int = 0x07
     const val TYPE_TIMESYNC_RSP: Int = 0x08
     const val TYPE_MTU_PROBE: Int = 0x09

echolot-app/core-shizuku/build.gradle.kts

@@ -32,4 +32,8 @@ dependencies {
     implementation(libs.shizuku.provider)
     implementation(libs.kotlinx.coroutines.android)
     implementation(libs.kotlinx.serialization.json)
+    // JVM unit tests for the pure dump parsers (DumpParsers.kt) against the archived
+    // vendor fixtures — no device, no Android runtime.
+    testImplementation(libs.kotlin.test.junit)
+    testImplementation(libs.junit4)
 }

echolot-app/core-shizuku/src/main/kotlin/app/echo_lot/shizuku/DumpParsers.kt

@@ -0,0 +1,174 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.shizuku
+
+/**
+ * Parsed view of one IPv6 default route from `ip -6 route show table all`.
+ *
+ * [table] stays a string: Android's per-network route tables use ids past Int range (the Lenovo
+ * TB330FU prints `table 1000000015`), and `table local` is not a number at all — parsing to a
+ * numeric type either overflows or silently drops rows, and the id is only ever compared, never
+ * computed with.
+ */
+data class V6DefaultRoute(
+    /** Link-local address of the advertising router; null for gateway-less defaults (dummy0). */
+    val gateway: String?,
+    val dev: String,
+    val table: String?, // null = main table (`ip` omits the token there)
+    val proto: String?, // "ra" marks a route installed from a Router Advertisement
+    val metric: Long?,
+    /** Remaining RA route lifetime (`expires NNNsec`); null when the route does not age out. */
+    val expiresSec: Long?,
+)
+
+/** One `ip neigh show` row. [lladdr] is null for FAILED/INCOMPLETE entries — the kernel tried to
+ *  resolve and has nothing, which is itself signal. */
+data class NeighborEntry(
+    val ip: String,
+    val dev: String?,
+    val lladdr: String?,
+    val state: String?, // REACHABLE/STALE/FAILED/... — kept verbatim, the kernel's vocabulary
+    val router: Boolean,
+)
+
+/** A NEIGH transition seen inside the `ip monitor` window. */
+data class NeighborEvent(val entry: NeighborEntry, val deleted: Boolean)
+
+/**
+ * Pure-string parsers for the shell battery's `ip` command outputs. No Android imports on
+ * purpose: these run (and are unit-tested) on the JVM against the real vendor dumps archived
+ * from the prober, which is the only way to catch a vendor format drift before it ships.
+ *
+ * All parsers degrade to an empty result on missing or unrecognized input — the battery's
+ * captures are best-effort (the Lenovo's `ip monitor` times out under newProcess, the
+ * UserService path prepends a stray `uid=2000` line, evidence strings are trimmed mid-line
+ * at 1200 chars), so an exception here would turn a degraded capture into a lost test.
+ */
+object DumpParsers {
+
+    /** True when [raw] is real command output rather than an executor error sentinel. */
+    fun captureUsable(raw: String?): Boolean {
+        if (raw.isNullOrBlank()) return false
+        val t = raw.trimStart()
+        return !t.startsWith("SHIZUKU_") && !t.startsWith("EXEC_") && !t.startsWith("NEWPROCESS_")
+    }
+
+    /** Extracts every `default …` route from `ip -6 route show table all` output. */
+    fun parseV6DefaultRoutes(raw: String?): List<V6DefaultRoute> {
+        if (!captureUsable(raw)) return emptyList()
+        val routes = ArrayList<V6DefaultRoute>()
+        for (line in raw!!.lineSequence()) {
+            val tok = line.trim().split(WS)
+            if (tok.firstOrNull() != "default") continue
+            var gateway: String? = null; var dev: String? = null; var table: String? = null
+            var proto: String? = null; var metric: Long? = null; var expires: Long? = null
+            var i = 1
+            while (i < tok.size - 1) {
+                when (tok[i]) {
+                    "via" -> gateway = tok[i + 1]
+                    "dev" -> dev = tok[i + 1]
+                    "table" -> table = tok[i + 1]
+                    "proto" -> proto = tok[i + 1]
+                    "metric" -> metric = tok[i + 1].toLongOrNull()
+                    // `expires 1269sec` — the unit is glued to the number.
+                    "expires" -> expires = tok[i + 1].removeSuffix("sec").toLongOrNull()
+                }
+                i++
+            }
+            // A default route without a device is not something `ip` prints; treat it as a
+            // truncated/garbled line rather than fabricating a partial route.
+            if (dev != null) routes.add(V6DefaultRoute(gateway, dev, table, proto, metric, expires))
+        }
+        return routes
+    }
+
+    /**
+     * Maps interface name → link-layer address from `ip addr show`. Only `link/ether` counts:
+     * loopback/ipip/gre pseudo-addresses are not identities, and the RA-source cross-reference
+     * this feeds compares Ethernet MACs.
+     */
+    fun parseInterfaceMacs(raw: String?): Map<String, String> {
+        if (!captureUsable(raw)) return emptyMap()
+        val macs = LinkedHashMap<String, String>()
+        var current: String? = null
+        for (line in raw!!.lineSequence()) {
+            val header = STANZA_HEADER.find(line)
+            if (header != null) {
+                // "5: tunl0@NONE:" — the name is the part before an optional @suffix.
+                current = header.groupValues[1].substringBefore('@')
+                continue
+            }
+            val dev = current ?: continue
+            val tok = line.trim().split(WS)
+            if (tok.size >= 2 && tok[0] == "link/ether" && MAC.matches(tok[1])) {
+                macs.putIfAbsent(dev, tok[1])
+            }
+        }
+        return macs
+    }
+
+    /** Parses `ip neigh show` output into entries; non-neighbor lines (uid noise) are skipped. */
+    fun parseNeighbors(raw: String?): List<NeighborEntry> {
+        if (!captureUsable(raw)) return emptyList()
+        return raw!!.lineSequence()
+            .mapNotNull { parseNeighborTokens(it.trim().split(WS)) }
+            .toList()
+    }
+
+    /**
+     * Extracts NEIGH transitions from an `ip monitor all` capture. Each event line carries a
+     * `[NEIGH]` label (other families — ROUTE, ADDR, LINK — are ignored) and deletions are
+     * printed as `Deleted <entry>`. An empty result is normal: a quiet 5 s window sees nothing.
+     */
+    fun parseNeighborEvents(raw: String?): List<NeighborEvent> {
+        if (!captureUsable(raw)) return emptyList()
+        val events = ArrayList<NeighborEvent>()
+        for (line in raw!!.lineSequence()) {
+            val m = MONITOR_LABEL.find(line.trim()) ?: continue
+            if (!m.groupValues[1].equals("NEIGH", ignoreCase = true)) continue
+            var rest = line.trim().removeRange(m.range).trim()
+            val deleted = rest.startsWith("Deleted ", ignoreCase = true)
+            if (deleted) rest = rest.substring("Deleted ".length)
+            parseNeighborTokens(rest.split(WS))?.let { events.add(NeighborEvent(it, deleted)) }
+        }
+        return events
+    }
+
+    /**
+     * (ip → lladdr) for every neighbor that has one. This is the comparison surface the future
+     * gateway-MAC-change finding diffs across runs, so it is computed here — in the tested,
+     * pure layer — rather than re-derived from JSON by each consumer.
+     */
+    fun lladdrByIp(neighbors: List<NeighborEntry>): Map<String, String> =
+        neighbors.mapNotNull { n -> n.lladdr?.let { n.ip to it } }.toMap()
+
+    /** One neighbor row: `<ip> dev <if> [lladdr <mac>] [router] [proxy] <STATE>`. */
+    private fun parseNeighborTokens(tok: List<String>): NeighborEntry? {
+        val ip = tok.firstOrNull() ?: return null
+        // The first token must look like an address — this is what drops the UserService path's
+        // stray "uid=2000" line and any grep noise without needing to know every noise shape.
+        if (!IP_LIKE.matches(ip) || (!ip.contains('.') && !ip.contains(':'))) return null
+        var dev: String? = null; var lladdr: String? = null; var state: String? = null
+        var router = false
+        var i = 1
+        while (i < tok.size) {
+            when (tok[i]) {
+                "dev" -> { dev = tok.getOrNull(i + 1); i++ }
+                "lladdr" -> { lladdr = tok.getOrNull(i + 1); i++ }
+                "router" -> router = true
+                "proxy" -> {} // recorded nowhere: proxy entries have no bearing on ARP watching
+                else -> if (STATE.matches(tok[i])) state = tok[i]
+            }
+            i++
+        }
+        return NeighborEntry(ip, dev, lladdr, state, router)
+    }
+
+    private val WS = Regex("\\s+")
+    private val STANZA_HEADER = Regex("^\\d+:\\s+([^:\\s]+):")
+    private val MAC = Regex("^[0-9a-fA-F]{2}(:[0-9a-fA-F]{2}){5}$")
+    private val IP_LIKE = Regex("^[0-9a-fA-F:.]+(%[\\w-]+)?$")
+    private val STATE = Regex("^(REACHABLE|STALE|DELAY|PROBE|FAILED|INCOMPLETE|PERMANENT|NOARP|NONE)$")
+    private val MONITOR_LABEL = Regex("^\\[(\\w+)]")
+}

echolot-app/core-shizuku/src/main/kotlin/app/echo_lot/shizuku/ShizukuAvailability.kt

@@ -98,20 +98,32 @@ object ShizukuAvailability {
             .addFlags(android.content.Intent.FLAG_ACTIVITY_NEW_TASK)
 
     /**
-     * Reports the state now and on every binder transition. Returns a function that removes the
-     * listeners again (call it from onCleared).
+     * Reports the state now, on every binder transition, and when a permission request is
+     * answered. Returns a function that removes the listeners again (call it from onCleared).
+     *
+     * The permission listener matters as much as the binder ones: granting permission does not
+     * make the binder arrive or die, so without it the banner still read "running but not
+     * authorised" after the user had just authorised it — the one moment they are looking for
+     * confirmation that it worked.
+     *
+     * It is still not sufficient on its own. Permission can be granted inside Shizuku's own app,
+     * where nothing calls back into this process at all, so callers should re-check on resume as
+     * well; see [current].
      */
     fun observe(context: Context, onChange: (State) -> Unit): () -> Unit {
         val app = context.applicationContext
         val received = Shizuku.OnBinderReceivedListener { onChange(current(app)) }
         val dead = Shizuku.OnBinderDeadListener { onChange(current(app)) }
+        val permission = Shizuku.OnRequestPermissionResultListener { _, _ -> onChange(current(app)) }
         // "Sticky" fires immediately if the binder already arrived before we registered.
         runCatching { Shizuku.addBinderReceivedListenerSticky(received) }
         runCatching { Shizuku.addBinderDeadListener(dead) }
+        runCatching { Shizuku.addRequestPermissionResultListener(permission) }
         onChange(current(app))
         return {
             runCatching { Shizuku.removeBinderReceivedListener(received) }
             runCatching { Shizuku.removeBinderDeadListener(dead) }
+            runCatching { Shizuku.removeRequestPermissionResultListener(permission) }
         }
     }
 }

echolot-app/core-shizuku/src/main/kotlin/app/echo_lot/shizuku/ShizukuProbe.kt

@@ -10,15 +10,24 @@ import app.echo_lot.measurement.TestType
 import app.echo_lot.measurement.Tier
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.JsonObject
 import kotlinx.serialization.json.buildJsonObject
 import kotlinx.serialization.json.put
+import kotlinx.serialization.json.putJsonArray
+import kotlinx.serialization.json.putJsonObject
+import kotlinx.serialization.json.addJsonObject
 
 /**
  * The Shizuku shell-tier probe: runs the privileged command battery (neighbor table, RA routes
  * with lifetimes, netlink monitor, IpClient DHCP logs, wifi dump) that the app UID cannot, and
- * captures the real per-device dump formats the production parsers must handle. Emitted as a
- * shizuku-tier `link.ip_monitor` test (the representative shell-tier link test); `exec_path`
- * records whether the UserService or the newProcess fallback carried it.
+ * captures the real per-device dump formats the production parsers must handle. Emits three
+ * shizuku-tier tests from the one battery:
+ *  - `link.ip_monitor` — the raw captures (the shell tier's ground truth), `exec_path` records
+ *    whether the UserService or the newProcess fallback carried it;
+ *  - `link.ra_source` — parsed from the v6 route table + `ip addr`: who advertises IPv6 here;
+ *  - `sec.arp_watch` — parsed from the neighbor table + monitor window: (ip → lladdr) pairs for
+ *    gateway-MAC-change detection.
+ * The battery runs once; the derived tests parse its captures, so they share its time window.
  */
 class ShizukuProbe {
     val type = TestType.LINK_IP_MONITOR
@@ -34,24 +43,34 @@ class ShizukuProbe {
         "wifi_dump" to "dumpsys wifi 2>/dev/null | grep -iA1 -m 20 -e 'mDhcpResults' -e 'Gateway' -e 'DNS' || true",
     )
 
-    /** Runs the battery and returns a Test. [uuid]/[monoNs] come from the run's id/clock source. */
-    suspend fun run(context: Context, uuid: () -> String, monoNs: () -> Long): Test = withContext(Dispatchers.IO) {
-        val id = uuid()
+    /**
+     * Runs the battery and returns the three tests, battery first. [uuid]/[monoNs] come from the
+     * run's id/clock source. When the shell tier is unavailable all three come back UNSUPPORTED —
+     * one silent test would leave the other two types missing from the document, which reads as
+     * "never attempted" rather than "tier absent".
+     */
+    suspend fun run(context: Context, uuid: () -> String, monoNs: () -> Long): List<Test> = withContext(Dispatchers.IO) {
         val started = monoNs()
         val runner = ShizukuRunner(context)
         val st = runner.status()
 
-        fun envelope(status: TestStatus, evidence: kotlinx.serialization.json.JsonObject, metrics: kotlinx.serialization.json.JsonObject? = null) =
-            Test(id = id, type = type, tier = tier, startedMonoNs = started, endedMonoNs = monoNs(),
+        fun envelope(type: String, status: TestStatus, evidence: JsonObject, metrics: JsonObject? = null) =
+            Test(id = uuid(), type = type, tier = tier, startedMonoNs = started, endedMonoNs = monoNs(),
                 status = status, evidence = evidence, metrics = metrics)
 
+        fun allUnsupported(evidence: JsonObject) = listOf(
+            envelope(TestType.LINK_IP_MONITOR, TestStatus.UNSUPPORTED, evidence),
+            envelope(TestType.LINK_RA_SOURCE, TestStatus.UNSUPPORTED, evidence),
+            envelope(TestType.SEC_ARP_WATCH, TestStatus.UNSUPPORTED, evidence),
+        )
+
         if (!st.binderAlive) {
-            return@withContext envelope(TestStatus.UNSUPPORTED, buildJsonObject {
+            return@withContext allUnsupported(buildJsonObject {
                 put("binder_alive", false); put("detail", "Shizuku not running")
             })
         }
         if (!st.permissionGranted && !runner.requestPermission()) {
-            return@withContext envelope(TestStatus.UNSUPPORTED, buildJsonObject {
+            return@withContext allUnsupported(buildJsonObject {
                 put("binder_alive", true); put("permission", false)
             })
         }
@@ -77,6 +96,125 @@ class ShizukuProbe {
             ok >= 1 -> TestStatus.PARTIAL
             else -> TestStatus.FAILED
         }
-        envelope(status, evidence, metrics)
+        listOf(
+            envelope(type, status, evidence, metrics),
+            raSourceTest(batch, ::envelope),
+            arpWatchTest(batch, ::envelope),
+        )
+    }
+
+    /** `link.ra_source` from the battery's `ip -6 route` / `ip addr` / `ip neigh` captures. */
+    private fun raSourceTest(
+        batch: ShizukuRunner.BatchResult,
+        envelope: (String, TestStatus, JsonObject, JsonObject?) -> Test,
+    ): Test {
+        val routeRaw = batch.results["ip6_route"]
+        if (!DumpParsers.captureUsable(routeRaw)) {
+            // The source command failed (executor sentinel or empty) — say so instead of
+            // presenting "no default routes" as a measurement of the network.
+            return envelope(TestType.LINK_RA_SOURCE, TestStatus.SKIPPED, buildJsonObject {
+                put("exec_path", batch.execPath)
+                put("reason", "ip -6 route capture unavailable: ${(routeRaw ?: "absent").take(80)}")
+            }, null)
+        }
+        val routes = DumpParsers.parseV6DefaultRoutes(routeRaw)
+        val macs = DumpParsers.parseInterfaceMacs(batch.results["ip_addr"])
+        // The RA sender's own identity: its link-local gateway address resolved through the
+        // neighbor table gives the router's MAC, which is what survives address renumbering.
+        val neighMacs = DumpParsers.lladdrByIp(DumpParsers.parseNeighbors(batch.results["ip_neigh"]))
+
+        val evidence = buildJsonObject {
+            put("exec_path", batch.execPath)
+            putJsonArray("default_routes") {
+                for (r in routes) addJsonObject {
+                    r.gateway?.let { put("gateway", it) }
+                    put("dev", r.dev)
+                    r.table?.let { put("table", it) }
+                    r.proto?.let { put("proto", it) }
+                    r.metric?.let { put("metric", it) }
+                    r.expiresSec?.let { put("expires_sec", it) }
+                    r.gateway?.let { gw -> neighMacs[gw]?.let { put("gateway_lladdr", it) } }
+                }
+            }
+            putJsonObject("interface_mac") {
+                // Only interfaces that actually carry a default route: the full MAC inventory
+                // belongs to the raw capture, not to this test's claim.
+                for (dev in routes.map { it.dev }.distinct()) macs[dev]?.let { put(dev, it) }
+            }
+        }
+        val metrics = buildJsonObject {
+            put("routes_total", routes.size)
+            put("routes_ra", routes.count { it.proto == "ra" })
+        }
+        val status = when {
+            routes.any { it.proto == "ra" } -> TestStatus.OK
+            // Routes parsed but none RA-installed, or a capture we couldn't parse a single
+            // default from: could be a genuinely RA-less link, could be vendor format drift —
+            // PARTIAL keeps it visible either way instead of quietly claiming success.
+            else -> TestStatus.PARTIAL
+        }
+        return envelope(TestType.LINK_RA_SOURCE, status, evidence, metrics)
+    }
+
+    /** `sec.arp_watch` from the battery's `ip neigh` snapshot + `ip monitor` window. */
+    private fun arpWatchTest(
+        batch: ShizukuRunner.BatchResult,
+        envelope: (String, TestStatus, JsonObject, JsonObject?) -> Test,
+    ): Test {
+        val neighRaw = batch.results["ip_neigh"]
+        val monitorRaw = batch.results["ip_monitor"]
+        val neighUsable = DumpParsers.captureUsable(neighRaw)
+        // The monitor window is best-effort (EXEC_TIMEOUT under newProcess on the Lenovo); the
+        // snapshot alone still yields the (ip → lladdr) pairs the MAC-change finding diffs.
+        val monitorRan = DumpParsers.captureUsable(monitorRaw)
+        if (!neighUsable && !monitorRan) {
+            return envelope(TestType.SEC_ARP_WATCH, TestStatus.SKIPPED, buildJsonObject {
+                put("exec_path", batch.execPath)
+                put("reason", "ip neigh capture unavailable: ${(neighRaw ?: "absent").take(80)}")
+            }, null)
+        }
+        val neighbors = DumpParsers.parseNeighbors(neighRaw)
+        val events = DumpParsers.parseNeighborEvents(monitorRaw)
+
+        val evidence = buildJsonObject {
+            put("exec_path", batch.execPath)
+            putJsonArray("neighbors") {
+                for (n in neighbors) addJsonObject {
+                    put("ip", n.ip)
+                    n.dev?.let { put("dev", it) }
+                    n.lladdr?.let { put("lladdr", it) }
+                    n.state?.let { put("state", it) }
+                    if (n.router) put("router", true)
+                }
+            }
+            // The comparison surface, precomputed: a MAC-change finding diffs this map between
+            // runs without re-walking the neighbor array.
+            putJsonObject("lladdr_by_ip") {
+                for ((ip, mac) in DumpParsers.lladdrByIp(neighbors)) put(ip, mac)
+            }
+            put("monitor_ran", monitorRan)
+            if (!monitorRan) put("monitor_reason", (monitorRaw ?: "absent").take(80))
+            putJsonArray("monitor_events") {
+                for (e in events) addJsonObject {
+                    put("ip", e.entry.ip)
+                    e.entry.dev?.let { put("dev", it) }
+                    e.entry.lladdr?.let { put("lladdr", it) }
+                    e.entry.state?.let { put("state", it) }
+                    if (e.deleted) put("deleted", true)
+                }
+            }
+        }
+        val metrics = buildJsonObject {
+            put("neighbors_total", neighbors.size)
+            put("neighbors_with_lladdr", neighbors.count { it.lladdr != null })
+            put("monitor_events", events.size)
+        }
+        val status = when {
+            neighbors.isNotEmpty() -> TestStatus.OK
+            // A snapshot that parsed to nothing (or a monitor-only capture) is thin evidence:
+            // usable command output with zero entries is unusual enough to flag, not to fail.
+            else -> TestStatus.PARTIAL
+        }
+        return envelope(TestType.SEC_ARP_WATCH, status, evidence, metrics)
     }
 }

echolot-app/core-shizuku/src/test/kotlin/app/echo_lot/shizuku/DumpParsersTest.kt

@@ -0,0 +1,303 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.shizuku
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+/**
+ * The fixtures below are the REAL shell-battery captures from the two archived prober reports
+ * (echolot-prober/reports/CPH2747-android16-sdk36-build5.json — OnePlus 15, UserService path;
+ * TB330FU-android15-sdk35-build5.json — Lenovo TB330FU, newProcess fallback), trimmed to the
+ * relevant lines but otherwise verbatim. That includes their warts on purpose: the UserService
+ * path's stray `uid=2000` first line, the 1200-char evidence trim cutting the last line mid-word,
+ * the Lenovo's 10-digit route table ids and its `EXEC_TIMEOUT(newProcess)` monitor sentinel.
+ * A parser that only survives clean textbook output has not been tested.
+ */
+class DumpParsersTest {
+
+    // ---- OnePlus 15 (CPH2747, Android 16) — UserService exec path ----
+
+    private val onePlusIp6Route = """
+        uid=2000
+        fe80::/64 dev wlan0 table 1028 proto kernel metric 256 pref medium
+        fe80::/64 dev wlan0 table 1028 proto static metric 1024 pref medium
+        default via fe80::7a9a:18ff:fe54:b8f9 dev wlan0 table 1028 proto ra metric 1024 expires 1269sec pref medium
+        fe80::/64 dev vgate0 table 1031 proto kernel metric 256 pref medium
+        2001:4bb8:417:bd78::/64 dev rmnet_data4 table 1032 proto kernel metric 256 pref medium
+        2001:4bb8:417:bd78::/64 dev rmnet_data4 table 1032 proto static metric 1024 pref medium
+        fe80::/64 dev rmnet_data4 table 1032 proto kernel metric 256 pref medium
+        default via fe80::246f:12be:21ef:1b54 dev rmnet_data4 table 1032 proto ra metric 1024 expires 64373sec hoplimit 255 pref medium
+        2001:4bb8:2fb:fe4c::/64 dev rmnet_data2 table 1000000022 proto static metric 1024 pref medium
+        fe80::/64 dev wlan0 table 1000000028 proto static metric 1024 pref medium
+        2001:4bb8:417:bd78::/64 dev rmnet_data4 table 1000000032 proto static metric 1024 pref medium
+        fe80::/64 dev dummy0 table 1002 proto kernel metric 256 pref medium
+        default dev dummy0 table 1002 proto static metric 1024 pref medium
+        fe80::/64 dev ifb0 table 1003 proto kernel metric 256 pref medium
+        fe80::/64 dev ifb1 table 1004 proto kerne
+    """.trimIndent()
+
+    private val onePlusIpNeigh = """
+        uid=2000
+        10.13.102.111 dev wlan0  FAILED
+        10.13.102.50 dev wlan0 lladdr 50:57:9c:4f:7a:3c STALE
+        10.13.102.31 dev wlan0 lladdr 98:5f:d3:f6:f1:75 STALE
+        10.13.102.116 dev wlan0 lladdr 0c:08:b4:03:68:0e STALE
+        10.13.102.120 dev wlan0 lladdr 0e:d8:14:58:6c:8b STALE
+        10.13.102.5 dev wlan0 lladdr 90:09:d0:1a:83:e4 STALE
+        10.13.102.1 dev wlan0 lladdr 78:9a:18:54:b8:f9 REACHABLE
+        10.13.102.21 dev wlan0 lladdr c8:7f:54:01:94:7c STALE
+        fe80::babe:f4ff:febc:caf9 dev wlan0 lladdr b8:be:f4:bc:ca:f9 REACHABLE
+        fe80::7a9a:18ff:fe54:b8f9 dev wlan0 lladdr 78:9a:18:54:b8:f9 router STALE
+        fe80::babe:f4ff:febc:cacf dev wlan0 lladdr b8:be:f4:bc:ca:cf REACHABLE
+        fe80::babe:f4ff:fec2:bf14 dev wlan0 lladdr b8:be:f4:c2:bf:14 REACHABLE
+    """.trimIndent()
+
+    // The 1200-char trim cut this capture off before wlan0's stanza — so the real archived
+    // evidence has NO MAC for the interface that carries the default route. The parser must
+    // yield what is there and nothing else; the probe records the gap instead of inventing one.
+    private val onePlusIpAddr = """
+        uid=2000
+        1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
+            link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
+            inet 127.0.0.1/8 scope host lo
+               valid_lft forever preferred_lft forever
+            inet6 ::1/128 scope host
+               valid_lft forever preferred_lft forever
+        2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
+            link/ether be:3d:e2:93:78:b9 brd ff:ff:ff:ff:ff:ff
+            inet6 fe80::bc3d:e2ff:fe93:78b9/64 scope link
+               valid_lft forever preferred_lft forever
+        3: ifb0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc htb state UNKNOWN group default qlen 1000
+            link/ether ba:6e:46:b5:3d:bb brd ff:ff:ff:ff:ff:ff
+        4: ifb1: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc htb state UNKNOWN group default qlen 1000
+            link/ether d6:2a:e2:f5:93:8f brd ff:ff:ff:ff:ff:ff
+        5: tunl0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN group default qlen 1000
+            link/ipip 0.0.0.0 brd 0.0.0.0
+        6: gre0@NONE: <NO
+    """.trimIndent()
+
+    // A monitor window that ran but saw nothing: the capture is "usable", just empty of events.
+    private val onePlusIpMonitor = "uid=2000"
+
+    // ---- Lenovo TB330FU (Android 15) — newProcess fallback ----
+
+    private val lenovoIp6Route = """
+        fe80::/64 dev wlan0 table 1000000015 proto static metric 1024 pref medium
+        fe80::/64 dev dummy0 table 1002 proto kernel metric 256 pref medium
+        default dev dummy0 table 1002 proto static metric 1024 pref medium
+        fe80::/64 dev wlan0 table 1015 proto kernel metric 256 pref medium
+        fe80::/64 dev wlan0 table 1015 proto static metric 1024 pref medium
+        default via fe80::7a9a:18ff:fe54:b8f9 dev wlan0 table 1015 proto ra metric 1024 expires 1622sec pref medium
+        local ::1 dev lo table local proto kernel metric 0 pref medium
+        local fe80::416:b9ff:feac:5b65 dev wlan0 table local proto kernel metric 0 pref medium
+        local fe80::1450:43ff:feec:93c4 dev dummy0 table local proto kernel metric 0 pref medium
+        multicast ff00::/8 dev dummy0 table local proto kernel metric 256 pref medium
+        multicast ff00::/8 dev wlan0 table local proto kernel metric 256 pref medium
+    """.trimIndent()
+
+    private val lenovoIpNeigh = """
+        10.13.102.21 dev wlan0 lladdr c8:7f:54:01:94:7c STALE
+        10.13.102.64 dev wlan0 lladdr b8:be:f4:c2:bf:14 STALE
+        10.13.102.5 dev wlan0 lladdr 90:09:d0:1a:83:e4 STALE
+        10.13.102.1 dev wlan0 lladdr 78:9a:18:54:b8:f9 STALE
+        10.13.102.79 dev wlan0 lladdr 02:11:32:25:63:bb STALE
+        fe80::babe:f4ff:febc:cacf dev wlan0 lladdr b8:be:f4:bc:ca:cf STALE
+        fe80::7a9a:18ff:fe54:b8f9 dev wlan0 lladdr 78:9a:18:54:b8:f9 router STALE
+        fe80::babe:f4ff:fec2:bf14 dev wlan0 lladdr b8:be:f4:c2:bf:14 STALE
+        fe80::babe:f4ff:febc:caf9 dev wlan0 lladdr b8:be:f4:bc:ca:f9 STALE
+    """.trimIndent()
+
+    private val lenovoIpAddr = """
+        1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
+            link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
+            inet 127.0.0.1/8 scope host lo
+               valid_lft forever preferred_lft forever
+        2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
+            link/ether 16:50:43:ec:93:c4 brd ff:ff:ff:ff:ff:ff
+            inet6 fe80::1450:43ff:feec:93c4/64 scope link
+               valid_lft forever preferred_lft forever
+        3: ifb0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 32
+            link/ether f6:d4:d4:9b:51:9c brd ff:ff:ff:ff:ff:ff
+        4: ifb1: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 32
+            link/ether fe:16:ea:60:a2:d1 brd ff:ff:ff:ff:ff:ff
+        5: tunl0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN group default qlen 1000
+            link/ipip 0.0.0.0 brd 0.0.0.0
+        7: gretap0@NONE: <BROADCAST,MULTICAST> mtu 1462 qdisc noop state DOWN group default qlen 1000
+            link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:f
+    """.trimIndent()
+
+    // On the Lenovo the 5 s monitor window exceeds the newProcess exec timeout — the executor's
+    // sentinel is all we get, and the arp_watch test must still stand on the snapshot alone.
+    private val lenovoIpMonitor = "EXEC_TIMEOUT(newProcess)"
+
+    // ---- link.ra_source: v6 default routes ----
+
+    @Test
+    fun onePlusDefaultRoutesParsed() {
+        val routes = DumpParsers.parseV6DefaultRoutes(onePlusIp6Route)
+        assertEquals(3, routes.size)
+
+        val wlan = routes.single { it.dev == "wlan0" }
+        assertEquals("fe80::7a9a:18ff:fe54:b8f9", wlan.gateway)
+        assertEquals("1028", wlan.table)
+        assertEquals("ra", wlan.proto)
+        assertEquals(1024L, wlan.metric)
+        assertEquals(1269L, wlan.expiresSec)
+
+        // The cellular default: `hoplimit 255` sits between expires and pref and must not derail
+        // the token walk.
+        val rmnet = routes.single { it.dev == "rmnet_data4" }
+        assertEquals("fe80::246f:12be:21ef:1b54", rmnet.gateway)
+        assertEquals("1032", rmnet.table)
+        assertEquals(64373L, rmnet.expiresSec)
+
+        // Android's gateway-less dummy0 default is a real route; it is the proto that tells a
+        // consumer it is not an RA.
+        val dummy = routes.single { it.dev == "dummy0" }
+        assertNull(dummy.gateway)
+        assertEquals("static", dummy.proto)
+        assertNull(dummy.expiresSec)
+    }
+
+    @Test
+    fun lenovoNumberedTablesAllCaptured() {
+        val routes = DumpParsers.parseV6DefaultRoutes(lenovoIp6Route)
+        // Two default routes: the RA one in table 1015 and the dummy0 one in 1002. The 10-digit
+        // table 1000000015 and the `table local` rows carry no default and must neither appear
+        // nor break parsing.
+        assertEquals(setOf("1002", "1015"), routes.map { it.table }.toSet())
+
+        val ra = routes.single { it.proto == "ra" }
+        assertEquals("fe80::7a9a:18ff:fe54:b8f9", ra.gateway)
+        assertEquals("wlan0", ra.dev)
+        assertEquals("1015", ra.table)
+        assertEquals(1622L, ra.expiresSec)
+    }
+
+    @Test
+    fun tenDigitTableIdOnADefaultRouteSurvives() {
+        // Not seen on a default route in the wild yet, but the Lenovo proves vendors put routes
+        // in tables past Int range — the day one holds a default, it must not overflow away.
+        val routes = DumpParsers.parseV6DefaultRoutes(
+            "default via fe80::1 dev wlan0 table 1000000015 proto ra metric 1024 expires 100sec pref medium"
+        )
+        assertEquals(1, routes.size)
+        assertEquals("1000000015", routes[0].table)
+        assertEquals(100L, routes[0].expiresSec)
+    }
+
+    // ---- link.ra_source: interface MACs ----
+
+    @Test
+    fun onePlusInterfaceMacsParsed() {
+        val macs = DumpParsers.parseInterfaceMacs(onePlusIpAddr)
+        assertEquals("be:3d:e2:93:78:b9", macs["dummy0"])
+        assertEquals("ba:6e:46:b5:3d:bb", macs["ifb0"])
+        // link/loopback and link/ipip are not identities.
+        assertFalse("lo" in macs)
+        assertFalse("tunl0" in macs)
+        // The capture is cut mid-stanza-header ("6: gre0@NONE: <NO") — no exception, no entry.
+        assertNull(macs["gre0"])
+    }
+
+    @Test
+    fun lenovoInterfaceMacsParsed() {
+        val macs = DumpParsers.parseInterfaceMacs(lenovoIpAddr)
+        assertEquals("16:50:43:ec:93:c4", macs["dummy0"])
+        assertEquals("fe:16:ea:60:a2:d1", macs["ifb1"])
+        // The @-suffixed stanza name resolves to the bare interface name.
+        assertEquals("00:00:00:00:00:00", macs["gretap0"])
+    }
+
+    // ---- sec.arp_watch: neighbor snapshot ----
+
+    @Test
+    fun onePlusNeighborsParsed() {
+        val n = DumpParsers.parseNeighbors(onePlusIpNeigh)
+        assertEquals(12, n.size) // the `uid=2000` noise line is not a neighbor
+
+        val failed = n.single { it.ip == "10.13.102.111" }
+        assertNull(failed.lladdr)
+        assertEquals("FAILED", failed.state)
+        assertEquals("wlan0", failed.dev)
+
+        val gw = n.single { it.ip == "10.13.102.1" }
+        assertEquals("78:9a:18:54:b8:f9", gw.lladdr)
+        assertEquals("REACHABLE", gw.state)
+
+        val v6gw = n.single { it.ip == "fe80::7a9a:18ff:fe54:b8f9" }
+        assertTrue(v6gw.router)
+        assertEquals("78:9a:18:54:b8:f9", v6gw.lladdr)
+    }
+
+    @Test
+    fun lenovoNeighborsParsed() {
+        val n = DumpParsers.parseNeighbors(lenovoIpNeigh)
+        assertEquals(9, n.size)
+        assertTrue(n.all { it.lladdr != null && it.state == "STALE" })
+        assertEquals(1, n.count { it.router })
+    }
+
+    @Test
+    fun lladdrByIpIsTheComparisonSurface() {
+        val pairs = DumpParsers.lladdrByIp(DumpParsers.parseNeighbors(onePlusIpNeigh))
+        // 12 neighbors, 11 with a MAC — the FAILED entry must drop out, or a diff against a
+        // later run would flag "null → MAC" as a gateway change.
+        assertEquals(11, pairs.size)
+        assertEquals("78:9a:18:54:b8:f9", pairs["10.13.102.1"])
+        assertFalse("10.13.102.111" in pairs)
+    }
+
+    // ---- sec.arp_watch: monitor window ----
+
+    @Test
+    fun monitorSentinelIsUnusableAndYieldsNoEvents() {
+        assertFalse(DumpParsers.captureUsable(lenovoIpMonitor))
+        assertTrue(DumpParsers.parseNeighborEvents(lenovoIpMonitor).isEmpty())
+    }
+
+    @Test
+    fun quietMonitorWindowIsUsableButEmpty() {
+        // OnePlus: the monitor ran (only the uid noise line came back) — "ran and saw nothing"
+        // must stay distinguishable from "never ran".
+        assertTrue(DumpParsers.captureUsable(onePlusIpMonitor))
+        assertTrue(DumpParsers.parseNeighborEvents(onePlusIpMonitor).isEmpty())
+    }
+
+    @Test
+    fun monitorNeighEventsParsedFromLabeledLines() {
+        // Synthetic, in `ip monitor all` label format — neither archived run caught a live
+        // transition, but the format is fixed by iproute2's print_neigh/print_headers.
+        val sample = """
+            [NEIGH]10.13.102.1 dev wlan0 lladdr 78:9a:18:54:b8:f9 REACHABLE
+            [NEIGH]Deleted 10.13.102.5 dev wlan0 lladdr 90:09:d0:1a:83:e4 STALE
+            [ROUTE]default via 10.13.102.1 dev wlan0 table 1015
+            [NEIGH]fe80::7a9a:18ff:fe54:b8f9 dev wlan0 lladdr 78:9a:18:54:b8:f9 router STALE
+        """.trimIndent()
+        val events = DumpParsers.parseNeighborEvents(sample)
+        assertEquals(3, events.size) // the ROUTE line belongs to a different family
+        assertEquals("10.13.102.1", events[0].entry.ip)
+        assertFalse(events[0].deleted)
+        assertTrue(events[1].deleted)
+        assertEquals("90:09:d0:1a:83:e4", events[1].entry.lladdr)
+        assertTrue(events[2].entry.router)
+    }
+
+    // ---- degradation: missing or garbage input ----
+
+    @Test
+    fun missingAndGarbageInputYieldsEmptyResultsNotExceptions() {
+        for (bad in listOf(null, "", "   \n ", "EXEC_TIMEOUT(newProcess)", "SHIZUKU_BINDER_DEAD",
+            "NEWPROCESS_UNAVAILABLE", "total garbage\nno routes here at all\ndefault", "default")) {
+            assertTrue(DumpParsers.parseV6DefaultRoutes(bad).isEmpty(), "routes from: $bad")
+            assertTrue(DumpParsers.parseNeighbors(bad).isEmpty(), "neighbors from: $bad")
+            assertTrue(DumpParsers.parseInterfaceMacs(bad).isEmpty(), "macs from: $bad")
+            assertTrue(DumpParsers.parseNeighborEvents(bad).isEmpty(), "events from: $bad")
+        }
+    }
+}

echolot-app/gradle/libs.versions.toml

@@ -8,6 +8,7 @@ lifecycle = "2.8.7"
 activityCompose = "1.9.3"
 composeBom = "2024.10.01"
 shizuku = "13.1.5"
+junit4 = "4.13.2"
 
 [libraries]
 kotlinx-serialization-json = { group = "org.jetbrains.kotlinx", name = "kotlinx-serialization-json", version.ref = "kotlinxSerialization" }
@@ -23,6 +24,10 @@ androidx-ui-tooling = { group = "androidx.compose.ui", name = "ui-tooling" }
 androidx-ui-tooling-preview = { group = "androidx.compose.ui", name = "ui-tooling-preview" }
 androidx-material3 = { group = "androidx.compose.material3", name = "material3" }
 shizuku-api = { group = "dev.rikka.shizuku", name = "api", version.ref = "shizuku" }
+# Android-module unit tests run on JUnit 4 (AGP's default); the JVM modules use kotlin("test")
+# with the JUnit Platform instead — that helper isn't available under AGP 9's built-in Kotlin.
+kotlin-test-junit = { group = "org.jetbrains.kotlin", name = "kotlin-test-junit", version.ref = "kotlin" }
+junit4 = { group = "junit", name = "junit", version.ref = "junit4" }
 shizuku-provider = { group = "dev.rikka.shizuku", name = "provider", version.ref = "shizuku" }
 
 [plugins]

echolot-app/scripts/enroll-link.sh

@@ -5,8 +5,13 @@
 # Mints an enrollment link on the probe server and prints it — as text, as a QR code if
 # `qrencode` is around, and as an adb command if a device is attached.
 #
-# The admin listener is localhost-only by design, so this goes over SSH. The link carries a
-# single-use bearer token: treat it like a password until it is redeemed.
+# The link is minted by the server binary on the host rather than over HTTP. The admin API this
+# used to call is gone: the admin UI that replaced it is authenticated, as it should be, and
+# adding a second unauthenticated door on loopback is what briefly exposed the old one to the
+# network. A root shell on the host needs no authentication anyway — whoever has one already has
+# every privilege the server has.
+#
+# The link carries a single-use bearer token: treat it like a password until it is redeemed.
 #
 # Usage: echolot-app/scripts/enroll-link.sh [note]
 set -euo pipefail
@@ -14,13 +19,18 @@ set -euo pipefail
 SSH_HOST="${ECHOLOT_SSH:-claude-echolot}"
 NOTE="${1:-manual}"
 
-MINTED=$(ssh -o BatchMode=yes "$SSH_HOST" \
-  "curl -s -X POST 'http://127.0.0.1:8444/admin/enroll-tokens?note=$NOTE'")
+# The env file is sourced rather than assumed: the state directory and the public URL live there,
+# and minting against the wrong state directory would produce a token the running server has
+# never heard of.
+REMOTE='set -a; . /etc/echolot/server.env; set +a;
+        exec /usr/local/bin/echolot-server --mint-enroll-token'
+RAW=$(ssh -o BatchMode=yes "$SSH_HOST" "sudo sh -c \"$REMOTE '$NOTE'\"" 2>/dev/null || true)
+URI=$(printf '%s' "$RAW" | tr -d '\r' | grep -m1 '^echolot://enroll' || true)
 
-URI=$(printf '%s' "$MINTED" | python -c 'import json,sys;print(json.load(sys.stdin).get("enroll_uri",""))')
 if [ -z "$URI" ]; then
-  echo "server returned no enroll_uri (needs server-v0.5.4+):" >&2
-  echo "$MINTED" >&2
+  echo "could not mint a link — needs a server with --mint-enroll-token (v0.9.7+)." >&2
+  echo "raw response:" >&2
+  printf '%s\n' "$RAW" >&2
   exit 1
 fi
 

server/README.md

@@ -106,9 +106,7 @@ ECHOLOT_UDP_LISTEN=203.0.113.10:8442,203.0.113.11:8442,[2001:db8::10]:8442,[2001
 
 Passing `--self-update-api` to `--install-systemd` additionally installs a daily randomized
 self-update timer (`echolot-server-update.timer`) that restarts the service after a successful
-update. Updates are checksum-verified against the release's `SHA256SUMS` (integrity, not
-authenticity — signature verification remains TODO before treating the update source as
-untrusted).
+update.
 
 ### Self-update (opt-in, native only)
 
@@ -119,14 +117,24 @@ echolot-server --self-update \
 
 Fetches the newest `server-v*` release asset for this OS/arch and atomically replaces the
 binary; systemd's `Restart=` brings up the new version. Run it from a systemd timer for
-unattended updates. TODO before enabling anywhere untrusted: signature verification of the
-downloaded asset.
+unattended updates.
+
+Releases are trusted by signature, not by host: CI signs `SHA256SUMS` with an ed25519 key that
+exists only in its secret store (`RELEASE_SIGNING_KEY`), and the updater verifies
+`SHA256SUMS.sig` against the public key baked into the binary before believing any checksum —
+an unsigned or re-signed release is refused, so a compromised Gitea can withhold updates but not
+inject one. Running your own release pipeline? Mint a keypair with
+`go run ./cmd/release-sign -gen`, set the secret, and point `ECHOLOT_SELF_UPDATE_PUBKEY` (or
+`--self-update-pubkey`) at your public key.
 
 ## First contact
 
 ```sh
-# 1. mint an enrollment token (admin listener is loopback-only)
-curl -s -X POST 'http://127.0.0.1:8444/admin/enroll-tokens?note=phone'
+# 1. mint an enrollment token (admin listener is loopback-only; authenticates as the
+#    break-glass admin — set that once with --set-admin-password)
+curl -s -u admin:<password> -H 'Accept: application/json' \
+  -X POST 'http://127.0.0.1:8444/admin/enroll-tokens?note=phone'
+# → { "token": "…", "expires_in_s": 86400, "enroll_uri": "echolot://enroll?…" }
 # 2. device enrolls with it (normally via the echolot:// QR code)
 curl -sk -X POST https://<host>:8443/v1/enroll -H 'Authorization: Bearer <token>'
 # 3. device fetches its profile
@@ -135,6 +143,47 @@ curl -sk https://<host>:8443/v1/profile -H 'Authorization: Bearer <credential>'
 
 The SPKI pin clients must verify is logged at startup (`pin-sha256`).
 
+## Dev relay (adb endpoint)
+
+Development scaffolding, not protocol: it appears in no capability list and in no measurement
+document, and `docs/probe-protocol.md` does not describe it.
+
+It exists because **mDNS does not cross subnets**. Android's wireless debugging advertises adbd's
+port over mDNS and rotates that port every few minutes, so a developer on another subnet cannot
+discover it at all. An Echolot instance running on the test LAN can — and relays it here.
+
+```
+POST /v1/devtools/adb-endpoint     control plane, device credential (same Bearer as /v1/sessions)
+  {"host":"10.13.102.128","port":45305,"device_name":"TB330FU","note":"…"}
+GET  /admin/adb-endpoints          admin UI, session cookie or HTTP Basic
+```
+
+Read it back from the developer's machine (the admin listener is loopback-only, so over the same
+SSH tunnel as everything else):
+
+```sh
+curl -s -u admin:<password> -H 'Accept: application/json' \
+  http://127.0.0.1:8444/admin/adb-endpoints
+# → [{"device":"…","host":"10.13.102.128","port":45305,"device_name":"TB330FU",
+#     "reported_at":"…","source_ip":"…","age_s":37}]
+```
+
+The same list is a card on the admin dashboard, so it is usable without curl.
+
+The newest report per submitting device wins — a rotated port makes the previous one wrong, not
+historical. The device id comes from the credential and `source_ip` from the connection, so neither
+is something a body can claim. `ECHOLOT_ADB_ENDPOINT_RETENTION_H` (default 24) bounds how long an
+entry lives; `0` keeps it until the device replaces it. The window exists because the value is a
+LAN address that stops being true within minutes: keeping it afterwards discloses the inside of
+someone's network in exchange for nothing.
+
+**Why it lives on these two listeners and nowhere else.** Its predecessor was a separate Python
+service wildcard-bound to `0.0.0.0:443`. That silently occupied port 443 on the addresses reserved
+for measurement — voiding the IPv4 interception proof for as long as it ran — and it accepted a port
+report from anyone who could reach it. So: no new listener, no new port, no wildcard bind, and
+nothing unauthenticated. The submit side is rate-limited by the existing §2.5 actions bucket
+(`ECHOLOT_RATE_ACTIONS_PER_MIN`).
+
 ## Development
 
 ```sh
@@ -144,7 +193,7 @@ go vet ./...
 
 CI (`.gitea/workflows/build-server.yml`): tests on every push touching `server/`;
 tagging `server-v1.2.3` builds + pushes the container image to the Gitea registry and
-attaches static linux amd64/arm64 binaries (+ SHA256SUMS) to a release — the same
+attaches static linux amd64/arm64 binaries (+ signed SHA256SUMS) to a release — the same
 artifacts `--self-update` consumes.
 
 ## TLS for the admin UI

server/cmd/echolot-server/main.go

@@ -46,6 +46,7 @@ import (
 	"echo-lot.app/server/internal/control"
 	"echo-lot.app/server/internal/dataplane"
 	"echo-lot.app/server/internal/oidc"
+	"echo-lot.app/server/internal/ratelimit"
 	"echo-lot.app/server/internal/runs"
 	"echo-lot.app/server/internal/selftest"
 	"echo-lot.app/server/internal/selfupdate"
@@ -110,21 +111,92 @@ func run() error {
 		return system.UninstallSystemd()
 	case actions.SetAdminPassword:
 		return setAdminPassword(cfg)
+	case actions.MintEnrollToken != "":
+		return mintEnrollToken(cfg, actions.MintEnrollToken)
 	case actions.SelfUpdate:
-		return selfupdate.Run(cfg.SelfUpdateAPI, Version)
+		return selfupdate.Run(cfg.SelfUpdateAPI, cfg.SelfUpdatePubKey, Version)
 	}
 	return serve(cfg)
 }
 
+// mintEnrollToken prints a §2.1 bootstrap link for a new device.
+//
+// The link is assembled here rather than by hand because it has to carry the public URL and the
+// base64 SPKI pin percent-encoded correctly, and a pin wrong by one character fails later as an
+// inscrutable TLS error rather than as a bad pin.
+func mintEnrollToken(cfg *config.Config, note string) error {
+	st, err := store.Open(cfg.StateDir)
+	if err != nil {
+		return fmt.Errorf("state store: %w", err)
+	}
+	cert, err := loadOrCreateCert(cfg)
+	if err != nil {
+		return fmt.Errorf("tls: %w", err)
+	}
+	pin, err := control.SpkiPinB64(cert)
+	if err != nil {
+		return fmt.Errorf("pin: %w", err)
+	}
+	tok, err := st.NewEnrollToken(24*time.Hour, note)
+	if err != nil {
+		return err
+	}
+	base := cfg.PublicControlURL
+	if base == "" {
+		return fmt.Errorf("set ECHOLOT_PUBLIC_URL so the link can say where to connect")
+	}
+	fmt.Println(control.EnrollmentURI(base, pin, tok))
+	// stderr, so piping the command somewhere yields the link alone.
+	fmt.Fprintln(os.Stderr, "\nSingle use, valid 24 hours. Treat it like a password until spent.")
+	return nil
+}
+
+// controlURL is the address devices connect to: the hostname that selects the pinned certificate.
+//
+// Falls back to the public URL when no separate control hostname is configured, so a server that
+// does not share the admin port keeps answering discovery with something usable.
+func controlURL(cfg *config.Config) string {
+	if cfg.ControlHostname == "" {
+		return cfg.PublicControlURL
+	}
+	return "https://" + cfg.ControlHostname
+}
+
 func serve(cfg *config.Config) error {
 	slog.Info("echolot-server starting", "version", Version, "mode",
 		map[bool]string{true: "container", false: "native"}[cfg.Docker],
 		"state_dir", cfg.StateDir)
 
+	// The reserved addresses' proof is only as good as 80/443 actually being free there.
+	// CheckReserved already keeps OUR listeners away, but a process outside this config pollutes
+	// them just as silently — the adb-beacon receiver on 0.0.0.0:443 did exactly that. So ask
+	// the OS, not the config. A hard stop for the same reason CheckReserved is one: the failure
+	// is invisible, and its first symptom is a measurement calling an intercepted network clean.
+	if reserved := cfg.ReservedIPs(); len(reserved) > 0 {
+		occupied, unverifiable := selftest.ReservedWebPortsFree(reserved)
+		if len(occupied) > 0 {
+			return fmt.Errorf(
+				"refusing to start: something outside this server is listening on reserved "+
+					"measurement address(es) %s\n"+
+					"The interception proof those addresses exist for is void while anything "+
+					"answers there.\nFind it with `ss -tlnp | grep -E ':(80|443) '`, stop it, "+
+					"or remove the address from ECHOLOT_RESERVED_ADDRS if it is no longer reserved",
+				strings.Join(occupied, ", "))
+		}
+		for _, u := range unverifiable {
+			// Not fatal: an address with a typo, or one this host no longer carries, is a
+			// config problem — refusing to serve over it would take the whole instrument down.
+			slog.Warn("could not verify a reserved web port is free", "addr", u)
+		}
+	}
+
 	st, err := store.Open(cfg.StateDir)
 	if err != nil {
 		return fmt.Errorf("state store: %w", err)
 	}
+	// Dev-relay breadcrumbs carry a LAN address, so they expire on a clock like the canary DNS
+	// log does rather than sitting in the state file until someone notices them.
+	st.SetADBEndpointRetention(time.Duration(cfg.ADBEndpointRetentionH) * time.Hour)
 	cert, err := loadOrCreateCert(cfg)
 	if err != nil {
 		return fmt.Errorf("tls: %w", err)
@@ -137,6 +209,16 @@ func serve(cfg *config.Config) error {
 
 	sessions := session.NewManager(15 * time.Minute)
 	dp := &dataplane.Server{Sessions: sessions}
+	// Spec §2.5 ceilings. Control plane answers 429; the data plane drops silently. 0 = off.
+	if cfg.RateUDPPps > 0 {
+		pps := float64(cfg.RateUDPPps)
+		// Burst of two seconds' worth: a 5000-packet train arrives as one burst by design.
+		dp.PacketRate = ratelimit.New(pps, 2*pps)
+	}
+	if cfg.RateUDPKbps > 0 {
+		bytesPerSec := float64(cfg.RateUDPKbps) * 125 // kbps -> bytes/s
+		dp.ByteRate = ratelimit.New(bytesPerSec, bytesPerSec)
+	}
 	// TCP echo shares the control cert for its elt-echo TLS variant.
 	tcpSrv := &tcpecho.Server{
 		TLSConfig: &tls.Config{Certificates: []tls.Certificate{cert}, MinVersion: tls.VersionTLS12},
@@ -215,7 +297,9 @@ func serve(cfg *config.Config) error {
 			"every upload will be refused")
 	}
 
+	ip4, ip6, ip4Alt, ip6Alt := cfg.MeasurementAddrs()
 	ctl := &control.Server{
+		IP4: ip4, IP6: ip6, IP4Alt: ip4Alt, IP6Alt: ip6Alt,
 		Store: st, Sessions: sessions, Name: cfg.Name,
 		UDPPort: mustPort(firstAddr(cfg.UDPListen)), TCPPort: mustPort(firstAddr(cfg.TCPListen)),
 		StunPort: mustPort(firstAddr(cfg.StunListen)), PinB64: pin, CertChain: cert.Certificate,
@@ -235,6 +319,12 @@ func serve(cfg *config.Config) error {
 		ctl.FragSend = dp.FragSend
 	}
 	ctl.DownThroughput = dp.DownThroughput
+	if cfg.RateSessionsPerMin > 0 {
+		ctl.RateSessions = ratelimit.New(float64(cfg.RateSessionsPerMin)/60, float64(cfg.RateSessionsPerMin))
+	}
+	if cfg.RateActionsPerMin > 0 {
+		ctl.RateActions = ratelimit.New(float64(cfg.RateActionsPerMin)/60, float64(cfg.RateActionsPerMin))
+	}
 
 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer stop()
@@ -316,6 +406,10 @@ func serve(cfg *config.Config) error {
 		ClientSecret: cfg.OIDCClientSecret,
 		Secure:       adminSecure,
 		EnrollLink:   ctl.EnrollmentLink,
+		// Where devices should connect, for /v1/discover. Derived from the control hostname so it
+		// cannot drift from the name that actually selects the pinned certificate.
+		ControlURL:   controlURL(cfg),
+		ServerName:   cfg.Name,
 		SelfTest:     func() any { return selftestPtr.Load() },
 		Version:      Version,
 	}
@@ -325,7 +419,17 @@ func serve(cfg *config.Config) error {
 	}
 	admin := ui.Handler()
 
-	adminSrv := &http.Server{Addr: cfg.AdminListen, Handler: admin, ReadHeaderTimeout: 10 * time.Second}
+	// One listener per configured address, all serving the same handler.
+	//
+	// Multi-address rather than a wildcard because this host reserves addresses for measurement:
+	// binding 0.0.0.0 would put the admin UI on port 443 of the reserved pair, and their value
+	// comes precisely from nothing answering there. Explicit addresses are also what let the
+	// service and management addresses differ without a second process.
+	adminAddrs := config.Addrs(cfg.AdminListen)
+	if len(adminAddrs) == 0 {
+		return fmt.Errorf("admin: no listen address configured")
+	}
+	var adminTLS *tls.Config
 	if cfg.AdminTLSCert != "" {
 		// Terminated here rather than behind a reverse proxy: this binary already serves TLS for
 		// the control plane, so it is reuse rather than new machinery, and one process with one
@@ -335,16 +439,92 @@ func serve(cfg *config.Config) error {
 		if err != nil {
 			return fmt.Errorf("admin TLS: %w", err)
 		}
-		adminSrv.TLSConfig = reloader.TLSConfig()
+		adminTLS = reloader.TLSConfig()
 		if exp := reloader.NotAfter(); !exp.IsZero() {
-			slog.Info("admin UI TLS", "listen", cfg.AdminListen, "cert_expires", exp.Format(time.RFC3339))
+			slog.Info("admin UI TLS", "listen", adminAddrs, "cert_expires", exp.Format(time.RFC3339))
 			if time.Until(exp) < 14*24*time.Hour {
 				slog.Warn("admin certificate expires soon", "expires", exp.Format(time.RFC3339))
 			}
 		}
-		go func() { errCh <- fmt.Errorf("admin: %w", adminSrv.ListenAndServeTLS("", "")) }()
-	} else {
-		go func() { errCh <- fmt.Errorf("admin: %w", adminSrv.ListenAndServe()) }()
+	}
+	// Kept for shutdown: each listener gets its own server, and a graceful stop has to reach all
+	// of them or an in-flight admin request is cut off mid-response on every address but one.
+	var adminSrvs []*http.Server
+	// Sharing port 443 between two services that cannot share a certificate. The name in the TLS
+	// handshake picks the certificate, and the name in the request picks the handler; both have to
+	// agree or a client would get the pinned certificate and the admin UI behind it.
+	//
+	// The control plane keeps its own listener as well. Devices enrolled before this carry the old
+	// URL in their settings, and taking that away would strand every one of them for the sake of a
+	// port number.
+	ctlHandler := ctl.Handler()
+	sharedCert := cert
+	// Which side of the port a request belongs to.
+	//
+	// The control hostname is the obvious case. A bare IP is the other one, and it matters: a
+	// client whose DNS has failed can still reach the server by an address it cached from the
+	// profile, and a measurement tool that cannot report from a broken network is useless
+	// precisely when it is needed. That client authenticates by pin, so the name it used to get
+	// here is not part of the trust decision.
+	//
+	// Safe to route that way because the admin UI is only ever reached by name: browsers always
+	// send SNI and nobody bookmarks an IP for a site with a Let's Encrypt certificate. Anything
+	// addressing this server numerically is a pinned client.
+	isControl := func(host string) bool {
+		if h, _, err := net.SplitHostPort(host); err == nil {
+			host = h
+		}
+		host = strings.Trim(host, "[]")
+		if cfg.ControlHostname != "" && strings.EqualFold(host, cfg.ControlHostname) {
+			return true
+		}
+		return net.ParseIP(host) != nil
+	}
+	pickCert := func(hi *tls.ClientHelloInfo) (*tls.Certificate, error) {
+		// No SNI at all also means a numeric client: every browser sends it.
+		if hi.ServerName == "" || isControl(hi.ServerName) {
+			return &sharedCert, nil
+		}
+		if adminTLS != nil && adminTLS.GetCertificate != nil {
+			return adminTLS.GetCertificate(hi)
+		}
+		return &sharedCert, nil
+	}
+	route := func(w http.ResponseWriter, r *http.Request) {
+		if isControl(r.Host) {
+			ctlHandler.ServeHTTP(w, r)
+			return
+		}
+		admin.ServeHTTP(w, r)
+	}
+	sharedTLS := &tls.Config{GetCertificate: pickCert, MinVersion: tls.VersionTLS12}
+	if cfg.ControlHostname != "" {
+		slog.Info("control plane shares the admin port",
+			"hostname", cfg.ControlHostname, "listen", adminAddrs)
+	}
+
+	for _, addr := range adminAddrs {
+		// Bound before the goroutine starts, so a bad address fails startup rather than being
+		// reported asynchronously after the process has already declared itself healthy.
+		ln, err := net.Listen("tcp", addr)
+		if err != nil {
+			return fmt.Errorf("admin listen %s: %w", addr, err)
+		}
+		srv := &http.Server{
+			Handler:           http.HandlerFunc(route),
+			ReadHeaderTimeout: 10 * time.Second,
+			TLSConfig:         sharedTLS,
+		}
+		adminSrvs = append(adminSrvs, srv)
+		go func(ln net.Listener, addr string) {
+			// Plaintext only where there is no certificate at all — checkAdminExposure has
+			// already refused that anywhere but loopback.
+			if adminTLS == nil && cfg.ControlHostname == "" {
+				errCh <- fmt.Errorf("admin %s: %w", addr, srv.Serve(ln))
+				return
+			}
+			errCh <- fmt.Errorf("admin %s: %w", addr, srv.ServeTLS(ln, "", ""))
+		}(ln, addr)
 	}
 
 	// ACME HTTP-01 responder. Permanent rather than started per renewal: nothing binds and
@@ -358,14 +538,21 @@ func serve(cfg *config.Config) error {
 		if err := acmehttp.EnsureWebroot(webroot); err != nil {
 			return fmt.Errorf("acme webroot: %w", err)
 		}
-		acmeSrv := &http.Server{
-			Addr:              cfg.ACMEHTTPListen,
-			Handler:           acmehttp.Handler(webroot, cfg.AdminBaseURL),
-			ReadHeaderTimeout: 10 * time.Second,
+		acmeHandler := acmehttp.Handler(webroot, cfg.AdminBaseURL)
+		for _, addr := range config.Addrs(cfg.ACMEHTTPListen) {
+			ln, err := net.Listen("tcp", addr)
+			if err != nil {
+				return fmt.Errorf("acme-http listen %s: %w", addr, err)
 			}
-		slog.Info("acme http-01 responder", "listen", cfg.ACMEHTTPListen, "webroot", webroot,
-			"redirects_to", cfg.AdminBaseURL)
-		go func() { errCh <- fmt.Errorf("acme-http: %w", acmeSrv.ListenAndServe()) }()
+			srv := &http.Server{Handler: acmeHandler, ReadHeaderTimeout: 10 * time.Second}
+			go func(ln net.Listener, addr string) {
+				errCh <- fmt.Errorf("acme-http %s: %w", addr, srv.Serve(ln))
+			}(ln, addr)
+		}
+		// Every address the name may resolve to needs the responder: the CA picks one, and a
+		// challenge that lands on an unbound address fails a renewal rather than a request.
+		slog.Info("acme http-01 responder", "listen", config.Addrs(cfg.ACMEHTTPListen),
+			"webroot", webroot, "redirects_to", cfg.AdminBaseURL)
 	}
 
 	// UDP data plane — one socket per configured address. Distinct sockets
@@ -431,7 +618,8 @@ func serve(cfg *config.Config) error {
 	var dnsTCP []net.Listener
 	if dnsAddrs := config.Addrs(cfg.DNSListen); len(dnsAddrs) > 0 && cfg.CanaryZone != "" {
 		v4, v6 := firstByFamily(dnsAddrs)
-		cd := canarydns.New(cfg.CanaryZone, cfg.Name, v4, v6)
+		cd := canarydns.New(cfg.CanaryZone, cfg.Name, v4, v6,
+			time.Duration(cfg.DNSLogRetentionH)*time.Hour)
 		for _, addr := range dnsAddrs {
 			ua, err := net.ResolveUDPAddr("udp", addr)
 			if err != nil {
@@ -457,7 +645,7 @@ func serve(cfg *config.Config) error {
 	}
 
 	slog.Info("listening",
-		"control", ctlAddrs, "admin", cfg.AdminListen, "udp", udpAddrs,
+		"control", ctlAddrs, "admin", adminAddrs, "udp", udpAddrs,
 		"tcp", config.Addrs(cfg.TCPListen), "stun", config.Addrs(cfg.StunListen),
 		"dns", config.Addrs(cfg.DNSListen), "capabilities", ctl.Capabilities)
 
@@ -467,7 +655,9 @@ func serve(cfg *config.Config) error {
 		shutCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		defer cancel()
 		_ = ctlSrv.Shutdown(shutCtx)
-		_ = adminSrv.Shutdown(shutCtx)
+		for _, srv := range adminSrvs {
+			_ = srv.Shutdown(shutCtx)
+		}
 		for _, c := range udpConns {
 			_ = c.Close()
 		}

server/cmd/release-sign/main.go

@@ -0,0 +1,84 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// release-sign signs a release manifest (SHA256SUMS) with the project's ed25519 key, producing
+// the detached <file>.sig that self-updating servers verify before trusting the checksums.
+//
+//	release-sign -gen                    mint a keypair (seed on stdout — store it as the CI
+//	                                     secret RELEASE_SIGNING_KEY; publish the public key)
+//	release-sign <file>                  sign; key read from $RELEASE_SIGNING_KEY, writes <file>.sig
+//	release-sign -verify -pub <b64> <f>  check <f> against <f>.sig — what the updater will do
+//
+// Run from CI (build-server.yml); the private key exists only in the Actions secret store, never
+// on the release host, which is the property that makes the signature worth having.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"echo-lot.app/server/internal/relsign"
+)
+
+func main() {
+	gen := flag.Bool("gen", false, "generate a keypair and exit")
+	verify := flag.Bool("verify", false, "verify <file> against <file>.sig instead of signing")
+	pub := flag.String("pub", "", "public key (base64) for -verify")
+	flag.Parse()
+
+	if err := run(*gen, *verify, *pub, flag.Args()); err != nil {
+		fmt.Fprintln(os.Stderr, "release-sign:", err)
+		os.Exit(1)
+	}
+}
+
+func run(gen, verify bool, pub string, args []string) error {
+	if gen {
+		pubB64, seedB64, err := relsign.GenerateKey()
+		if err != nil {
+			return err
+		}
+		fmt.Printf("public key (embed / ECHOLOT_SELF_UPDATE_PUBKEY):\n%s\n\n"+
+			"private key (CI secret RELEASE_SIGNING_KEY — this is the only copy):\n%s\n",
+			pubB64, seedB64)
+		return nil
+	}
+	if len(args) != 1 {
+		return fmt.Errorf("usage: release-sign [-gen | -verify -pub <b64>] <file>")
+	}
+	file := args[0]
+	data, err := os.ReadFile(file)
+	if err != nil {
+		return err
+	}
+
+	if verify {
+		if pub == "" {
+			return fmt.Errorf("-verify needs -pub")
+		}
+		sig, err := os.ReadFile(file + ".sig")
+		if err != nil {
+			return err
+		}
+		if err := relsign.Verify(pub, data, string(sig)); err != nil {
+			return err
+		}
+		fmt.Printf("%s: signature OK\n", file)
+		return nil
+	}
+
+	seed := os.Getenv("RELEASE_SIGNING_KEY")
+	if seed == "" {
+		return fmt.Errorf("RELEASE_SIGNING_KEY is not set — refusing to produce an unsigned release")
+	}
+	sig, err := relsign.Sign(seed, data)
+	if err != nil {
+		return err
+	}
+	if err := os.WriteFile(file+".sig", []byte(sig+"\n"), 0o644); err != nil {
+		return err
+	}
+	fmt.Printf("wrote %s.sig\n", file)
+	return nil
+}

server/go.mod

@@ -1,3 +1,5 @@
 module echo-lot.app/server
 
 go 1.24
+
+require github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e // indirect

server/go.sum

@@ -0,0 +1,2 @@
+github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e h1:MRM5ITcdelLK2j1vwZ3Je0FKVCfqOLp5zO6trqMLYs0=
+github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e/go.mod h1:XV66xRDqSt+GTGFMVlhk3ULuV0y9ZmzeVGR4mloJI3M=

server/internal/adminauth/adminauth.go

@@ -166,12 +166,21 @@ func (t *Throttle) Succeeded() {
 
 // ---- sessions ---------------------------------------------------------------------------
 
-// Session is an authenticated admin, however they proved it.
+// Session is an authenticated account, however it proved itself. Not necessarily an admin:
+// signing in and being allowed to administer the server are separate questions, and a plain user
+// gets a session so they can manage their own uploads.
 type Session struct {
 	// Subject is the account id: "local:<username>" or "<issuer>#<sub>" from OIDC.
 	Subject string
 	// Display is what the UI shows.
 	Display string
+	// Admin is authorisation, decided at sign-in and carried inside the signed payload.
+	//
+	// Inside, specifically — not derived later from the subject, and not stored beside the MAC.
+	// A flag outside the signature is a privilege escalation anyone can perform with a text
+	// editor, and re-deriving it per request would mean re-reading group membership from the IdP
+	// on a path that has no token to do it with.
+	Admin   bool
 	Expires time.Time
 }
 
@@ -203,12 +212,16 @@ func NewSecret() ([]byte, error) {
 
 var ErrSession = errors.New("session is not valid")
 
-// Issue returns the cookie value for a newly authenticated admin.
-func (s *Sessions) Issue(subject, display string) string {
+// Issue returns the cookie value for a newly authenticated account.
+func (s *Sessions) Issue(subject, display string, admin bool) string {
 	exp := time.Now().Add(s.ttl).Unix()
+	role := "u"
+	if admin {
+		role = "a"
+	}
 	payload := base64.RawURLEncoding.EncodeToString([]byte(subject)) + "." +
 		base64.RawURLEncoding.EncodeToString([]byte(display)) + "." +
-		strconv.FormatInt(exp, 10)
+		strconv.FormatInt(exp, 10) + "." + role
 	return payload + "." + s.mac(payload)
 }
 
@@ -225,7 +238,7 @@ func (s *Sessions) Parse(value string) (*Session, error) {
 		return nil, ErrSession
 	}
 	parts := strings.Split(payload, ".")
-	if len(parts) != 3 {
+	if len(parts) != 4 {
 		return nil, ErrSession
 	}
 	subject, err := base64.RawURLEncoding.DecodeString(parts[0])
@@ -243,7 +256,13 @@ func (s *Sessions) Parse(value string) (*Session, error) {
 	if time.Now().After(time.Unix(exp, 0)) {
 		return nil, fmt.Errorf("%w: expired", ErrSession)
 	}
-	return &Session{Subject: string(subject), Display: string(display), Expires: time.Unix(exp, 0)}, nil
+	// Anything that is not exactly the admin marker is a user. A malformed role must fail closed:
+	// the safe reading of an unparseable privilege claim is the smaller privilege.
+	admin := parts[3] == "a"
+	return &Session{
+		Subject: string(subject), Display: string(display),
+		Admin: admin, Expires: time.Unix(exp, 0),
+	}, nil
 }
 
 func (s *Sessions) mac(payload string) string {

server/internal/adminauth/adminauth_test.go

@@ -4,6 +4,8 @@
 package adminauth
 
 import (
+	"encoding/base64"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -96,7 +98,7 @@ func TestAnEmptyCredentialNeverVerifies(t *testing.T) {
 func TestSessionRoundTrip(t *testing.T) {
 	secret, _ := NewSecret()
 	s := NewSessions(secret, time.Hour)
-	got, err := s.Parse(s.Issue("local:admin", "Admin"))
+	got, err := s.Parse(s.Issue("local:admin", "Admin", true))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -110,7 +112,7 @@ func TestSessionRoundTrip(t *testing.T) {
 func TestTamperedSessionsAreRejected(t *testing.T) {
 	secret, _ := NewSecret()
 	s := NewSessions(secret, time.Hour)
-	good := s.Issue("local:admin", "Admin")
+	good := s.Issue("local:admin", "Admin", true)
 
 	parts := strings.Split(good, ".")
 	tampered := []string{
@@ -131,7 +133,7 @@ func TestTamperedSessionsAreRejected(t *testing.T) {
 func TestSessionsFromAnotherSecretAreRejected(t *testing.T) {
 	a, _ := NewSecret()
 	b, _ := NewSecret()
-	issued := NewSessions(a, time.Hour).Issue("local:admin", "Admin")
+	issued := NewSessions(a, time.Hour).Issue("local:admin", "Admin", true)
 	if _, err := NewSessions(b, time.Hour).Parse(issued); err == nil {
 		t.Fatal("a session signed with a different secret was accepted — rotating the secret " +
 			"must invalidate every existing session")
@@ -143,7 +145,7 @@ func TestExpiredSessionsAreRejected(t *testing.T) {
 	// A negative TTL is not reachable through NewSessions, so issue with a real one and check
 	// the boundary via a session that has already run out.
 	s := NewSessions(secret, time.Millisecond)
-	v := s.Issue("local:admin", "Admin")
+	v := s.Issue("local:admin", "Admin", true)
 	time.Sleep(10 * time.Millisecond)
 	if _, err := s.Parse(v); err == nil {
 		t.Fatal("an expired session was accepted")
@@ -201,3 +203,46 @@ func TestThrottleForgivesAfterAQuietPeriod(t *testing.T) {
 		t.Fatalf("an operator returning later was still throttled: %v", d)
 	}
 }
+
+// The admin flag is an authorisation decision carried in a cookie the client holds, so the
+// interesting cases are all about what happens when the client lies about it.
+func TestSessionAdminFlag(t *testing.T) {
+	s := NewSessions([]byte("secret"), time.Hour)
+
+	t.Run("round trips both ways", func(t *testing.T) {
+		admin, err := s.Parse(s.Issue("local:admin", "Admin", true))
+		if err != nil || !admin.Admin {
+			t.Fatalf("admin session did not survive: %+v err=%v", admin, err)
+		}
+		user, err := s.Parse(s.Issue("oidc#1", "Markus", false))
+		if err != nil || user.Admin {
+			t.Fatalf("user session came back as admin: %+v err=%v", user, err)
+		}
+	})
+
+	t.Run("promoting yourself invalidates the cookie", func(t *testing.T) {
+		// The whole point of putting the flag inside the MAC: editing it must break the signature
+		// rather than produce a valid admin session.
+		v := s.Issue("oidc#1", "Markus", false)
+		i := strings.LastIndex(v, ".")
+		tampered := strings.TrimSuffix(v[:i], ".u") + ".a" + v[i:]
+		if got, err := s.Parse(tampered); err == nil {
+			t.Fatalf("a self-promoted cookie was accepted as %+v", got)
+		}
+	})
+
+	t.Run("an unparseable role is not an admin", func(t *testing.T) {
+		// Fail closed: whatever a malformed privilege claim means, it does not mean "more access".
+		// Signed by us, so it passes the MAC — only the role parsing stands between it and admin.
+		exp := strconv.FormatInt(time.Now().Add(time.Hour).Unix(), 10)
+		payload := base64.RawURLEncoding.EncodeToString([]byte("oidc#1")) + "." +
+			base64.RawURLEncoding.EncodeToString([]byte("Markus")) + "." + exp + ".ADMIN"
+		sess, err := s.Parse(payload + "." + s.mac(payload))
+		if err != nil {
+			t.Fatalf("unexpected parse error: %v", err)
+		}
+		if sess.Admin {
+			t.Fatal("a role of \"ADMIN\" was treated as the admin marker")
+		}
+	})
+}

server/internal/adminui/adbendpoints.go

@@ -0,0 +1,66 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package adminui
+
+import (
+	"encoding/json"
+	"net/http"
+	"time"
+)
+
+// The read side of the dev relay (control/devtools.go submits, this reads back). It is here, in
+// the UI that already authenticates, rather than in a listener of its own — that is the lesson of
+// the beacon receiver it replaces, which was a separate unauthenticated service on port 443 of the
+// addresses reserved for measurement.
+
+// adbRow is one relayed endpoint as the API and the dashboard both see it.
+//
+// age_s is computed rather than left to the reader: the port it describes rotates every few
+// minutes, so how old the report is decides whether it is worth trying at all.
+type adbRow struct {
+	Device     string    `json:"device"`
+	Host       string    `json:"host"`
+	Port       int       `json:"port"`
+	DeviceName string    `json:"device_name,omitempty"`
+	Note       string    `json:"note,omitempty"`
+	ReportedAt time.Time `json:"reported_at"`
+	SourceIP   string    `json:"source_ip,omitempty"`
+	AgeS       int       `json:"age_s"`
+}
+
+// adbRows reads the store's live endpoints (already newest first, already aged out).
+func (s *Server) adbRows() []adbRow {
+	now := time.Now().UTC()
+	eps := s.Store.ADBEndpoints()
+	rows := make([]adbRow, 0, len(eps))
+	for _, e := range eps {
+		age := int(now.Sub(e.ReportedAt).Seconds())
+		if age < 0 {
+			age = 0 // a clock that ran backwards should read "just now", not negative
+		}
+		rows = append(rows, adbRow{
+			Device: e.Device, Host: e.Host, Port: e.Port,
+			DeviceName: e.DeviceName, Note: e.Note,
+			ReportedAt: e.ReportedAt, SourceIP: e.SourceIP, AgeS: age,
+		})
+	}
+	return rows
+}
+
+// adbEndpointsAPI is GET /admin/adb-endpoints — the developer's half of the relay.
+//
+// Authenticated exactly like the mint endpoint, so `curl -u admin:PASS` works from a script and a
+// signed-in browser session works without one. Admin-only: a LAN address and a debug port are the
+// operator's business, and a user's uploads are not made safer by handing out either.
+func (s *Server) adbEndpointsAPI(w http.ResponseWriter, r *http.Request) {
+	if _, ok := s.apiAdmin(w, r); !ok {
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	rows := s.adbRows()
+	if rows == nil {
+		rows = []adbRow{} // an empty list, never null: a caller should not have to special-case it
+	}
+	_ = json.NewEncoder(w).Encode(rows)
+}

server/internal/adminui/adbendpoints_test.go

@@ -0,0 +1,148 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package adminui
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"echo-lot.app/server/internal/store"
+)
+
+func adbFixture(t *testing.T) *Server {
+	t.Helper()
+	s := tokenFixture(t)
+	s.Store.SetADBEndpointRetention(24 * time.Hour)
+	now := time.Now().UTC()
+	for _, e := range []store.ADBEndpoint{
+		{Device: "dev-a", Host: "10.13.102.128", Port: 45305, DeviceName: "TB330FU",
+			SourceIP: "10.13.102.128", ReportedAt: now.Add(-10 * time.Minute)},
+		{Device: "dev-b", Host: "10.13.102.55", Port: 5555,
+			SourceIP: "10.13.102.55", ReportedAt: now.Add(-time.Minute)},
+	} {
+		if err := s.Store.PutADBEndpoint(e); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return s
+}
+
+// A LAN address and a live debug port are exactly what must not be readable by anyone who can
+// reach the listener — which is how the beacon receiver this replaces worked.
+func TestADBEndpointsReadRequiresAuth(t *testing.T) {
+	h := adbFixture(t).Handler()
+
+	req := httptest.NewRequest("GET", "/admin/adb-endpoints", nil)
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusUnauthorized || rec.Header().Get("WWW-Authenticate") == "" {
+		t.Fatalf("unauthenticated: code=%d, want 401 with a challenge", rec.Code)
+	}
+	if rec.Body.Len() > 0 && json.Valid(rec.Body.Bytes()) {
+		t.Fatalf("a refusal returned a JSON body: %s", rec.Body.String())
+	}
+
+	req = httptest.NewRequest("GET", "/admin/adb-endpoints", nil)
+	req.SetBasicAuth("admin", "wrong")
+	rec = httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("bad password: code=%d, want 401", rec.Code)
+	}
+}
+
+func TestADBEndpointsReadNewestFirst(t *testing.T) {
+	h := adbFixture(t).Handler()
+	req := httptest.NewRequest("GET", "/admin/adb-endpoints", nil)
+	req.SetBasicAuth("admin", "a-long-test-password")
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("code=%d body=%s", rec.Code, rec.Body.String())
+	}
+	var rows []adbRow
+	if err := json.Unmarshal(rec.Body.Bytes(), &rows); err != nil {
+		t.Fatal(err)
+	}
+	if len(rows) != 2 {
+		t.Fatalf("got %d rows, want 2: %s", len(rows), rec.Body.String())
+	}
+	if rows[0].Device != "dev-b" {
+		t.Fatalf("rows are not newest first: %+v", rows)
+	}
+	if rows[0].Host != "10.13.102.55" || rows[0].Port != 5555 || rows[0].SourceIP == "" {
+		t.Fatalf("row is missing what a developer came for: %+v", rows[0])
+	}
+	// age_s is the field that says whether the port is worth trying at all.
+	if rows[0].AgeS < 50 || rows[0].AgeS > 120 {
+		t.Fatalf("age_s = %d, want roughly 60", rows[0].AgeS)
+	}
+	if rows[1].AgeS <= rows[0].AgeS {
+		t.Fatalf("ages do not follow the ordering: %+v", rows)
+	}
+}
+
+// The card exists so the relay is usable without curl. Rendered here because a template error is
+// only found when the page is executed, not when it is parsed.
+func TestDashboardShowsTheRelayToAnAdmin(t *testing.T) {
+	s := adbFixture(t)
+	h := s.Handler()
+
+	req := httptest.NewRequest("GET", "/", nil)
+	req.AddCookie(&http.Cookie{
+		Name: sessionCookie, Value: s.Sessions.Issue("local:admin", "admin", true),
+	})
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("dashboard: code=%d", rec.Code)
+	}
+	for _, want := range []string{"Dev relay", "10.13.102.55:5555", "min ago"} {
+		if !strings.Contains(rec.Body.String(), want) {
+			t.Errorf("the dashboard card does not show %q", want)
+		}
+	}
+
+	// A plain user gets no rows at all — not an empty card, no card.
+	req = httptest.NewRequest("GET", "/", nil)
+	req.AddCookie(&http.Cookie{
+		Name: sessionCookie, Value: s.Sessions.Issue("oidc#someone", "Someone", false),
+	})
+	rec = httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if strings.Contains(rec.Body.String(), "10.13.102.55") {
+		t.Fatal("a non-admin session was shown a LAN address")
+	}
+}
+
+// The read is a GET, so a signed-in browser session must not be asked for a CSRF token it has no
+// form to carry — but a session that is not an administrator is still refused.
+func TestADBEndpointsReadFromABrowserSession(t *testing.T) {
+	s := adbFixture(t)
+	h := s.Handler()
+
+	for _, tc := range []struct {
+		name     string
+		admin    bool
+		wantCode int
+	}{
+		{"admin", true, http.StatusOK},
+		{"plain user", false, http.StatusForbidden},
+	} {
+		req := httptest.NewRequest("GET", "/admin/adb-endpoints", nil)
+		req.AddCookie(&http.Cookie{
+			Name:  sessionCookie,
+			Value: s.Sessions.Issue("local:admin", "admin", tc.admin),
+		})
+		rec := httptest.NewRecorder()
+		h.ServeHTTP(rec, req)
+		if rec.Code != tc.wantCode {
+			t.Errorf("%s: code=%d, want %d (%s)", tc.name, rec.Code, tc.wantCode, rec.Body.String())
+		}
+	}
+}

server/internal/adminui/auth.go

@@ -61,6 +61,10 @@ type Server struct {
 	// EnrollLink builds the §2.1 bootstrap link for a token. Injected rather than rebuilt here,
 	// so the SPKI pin and public URL stay owned by the control server that actually knows them.
 	EnrollLink func(token string) string
+	// ControlURL is where devices should actually connect, handed out by /v1/discover so the
+	// enrollment link can show the public name instead. ServerName is for display.
+	ControlURL string
+	ServerName string
 	// SelfTest and Version render on the dashboard.
 	SelfTest func() any
 	Version  string
@@ -77,19 +81,49 @@ func (s *Server) Handler() http.Handler {
 		fmt.Fprintf(w, `{"ok":true,"version":%q}`+"\n", s.Version)
 	})
 
+	// Unauthenticated on purpose, and deliberately says almost nothing: where the control plane
+	// is, and nothing about who may talk to it.
+	//
+	// This exists so an enrollment link can carry the name a person recognises while the app
+	// still connects to the name that selects the pinned certificate. It hands out an address,
+	// never a pin — the pin travels in the link itself. Serving the pin here would collapse
+	// pinning to whatever the CA system says, and pinning exists precisely to survive a
+	// certificate authority the operator does not control.
+	//
+	// So the worst an intercepted discovery can do is send a device to the wrong host, where the
+	// pin check fails. That is a denial of service, not a compromise.
+	mux.HandleFunc("GET /v1/discover", func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(map[string]string{
+			"control_url": s.ControlURL,
+			"name":        s.ServerName,
+		})
+	})
+
 	mux.HandleFunc("GET /login", s.loginForm)
 	mux.HandleFunc("POST /login", s.loginSubmit)
 	mux.HandleFunc("GET /auth/start", s.oidcStart)
 	mux.HandleFunc("GET /admin/callback", s.oidcCallback)
 	mux.HandleFunc("POST /logout", s.logout)
 
+	// Any signed-in account. These handlers scope what they show to the session themselves —
+	// an admin sees everything, a user sees their own devices and runs.
 	mux.HandleFunc("GET /", s.guard(s.dashboard))
 	mux.HandleFunc("GET /devices", s.guard(s.devices))
-	mux.HandleFunc("POST /devices/{id}/revoke", s.guard(s.revokeDevice))
-	mux.HandleFunc("POST /enroll-tokens", s.guard(s.mintToken))
 	mux.HandleFunc("GET /runs", s.guard(s.runsList))
 	mux.HandleFunc("GET /runs/{device}/{id}", s.guard(s.runView))
 	mux.HandleFunc("POST /runs/{device}/{id}/delete", s.guard(s.runDelete))
+	// Deleting your own upload is yours to do; revoking a device or minting an enrolment token
+	// affects the whole server, so those stay with the admin.
+	mux.HandleFunc("POST /devices/{id}/revoke", s.guard(s.adminOnly(s.revokeDevice)))
+	mux.HandleFunc("POST /enroll-tokens", s.guard(s.adminOnly(s.mintToken)))
+	// The spec-shaped mint endpoint (§2.1: {token, expires_in_s, enroll_uri}), for curl and
+	// scripts. Authenticates its own way — see apiAdmin — because guard's redirect-to-login is
+	// useless to a caller without a browser.
+	mux.HandleFunc("POST /admin/enroll-tokens", s.enrollTokensAPI)
+	// The dev relay's read side (adbendpoints.go), authenticated the same way and for the same
+	// reason: a developer reads it with curl from another subnet, where a login redirect is no use.
+	mux.HandleFunc("GET /admin/adb-endpoints", s.adbEndpointsAPI)
 
 	return mux
 }
@@ -102,7 +136,7 @@ func (s *Server) guard(h func(http.ResponseWriter, *http.Request, *adminauth.Ses
 			http.Redirect(w, r, "/login", http.StatusSeeOther)
 			return
 		}
-		if r.Method != http.MethodGet && r.Method != http.MethodHead {
+		if !safeMethod(r) {
 			// SameSite=Lax already blocks cross-site form posts in current browsers, but this
 			// is the control that does not depend on the browser being current.
 			if !s.csrfOK(r, sess) {
@@ -114,6 +148,13 @@ func (s *Server) guard(h func(http.ResponseWriter, *http.Request, *adminauth.Ses
 	}
 }
 
+// safeMethod reports whether a request only reads. CSRF protection applies to the others: there is
+// nothing for a cross-site form to ride on when the handler changes nothing, and demanding a token
+// on a GET would make a read endpoint unusable from the session that is already signed in.
+func safeMethod(r *http.Request) bool {
+	return r.Method == http.MethodGet || r.Method == http.MethodHead
+}
+
 func (s *Server) session(r *http.Request) *adminauth.Session {
 	c, err := r.Cookie(sessionCookie)
 	if err != nil {
@@ -140,10 +181,28 @@ func (s *Server) csrfOK(r *http.Request, sess *adminauth.Session) bool {
 	return r.PostFormValue(csrfField) == s.csrfToken(sess)
 }
 
-func (s *Server) setSession(w http.ResponseWriter, subject, display string) {
+// adminOnly refuses a handler to a signed-in account that is not an administrator.
+//
+// A separate wrapper rather than a check inside each handler: an authorisation rule that has to be
+// remembered in every handler is one that will eventually be forgotten in a new one, and the route
+// table is where someone looks to find out who may do what.
+func (s *Server) adminOnly(
+	h func(http.ResponseWriter, *http.Request, *adminauth.Session),
+) func(http.ResponseWriter, *http.Request, *adminauth.Session) {
+	return func(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
+		if !sess.Admin {
+			slog.Info("admin action refused", "account", sess.Subject, "path", r.URL.Path)
+			http.Error(w, "that action needs an administrator account", http.StatusForbidden)
+			return
+		}
+		h(w, r, sess)
+	}
+}
+
+func (s *Server) setSession(w http.ResponseWriter, subject, display string, admin bool) {
 	http.SetCookie(w, &http.Cookie{
 		Name:     sessionCookie,
-		Value:    s.Sessions.Issue(subject, display),
+		Value:    s.Sessions.Issue(subject, display, admin),
 		Path:     "/",
 		HttpOnly: true, // the cookie is a bearer credential; script has no business reading it
 		Secure:   s.Secure,
@@ -186,10 +245,45 @@ func (s *Server) loginSubmit(w http.ResponseWriter, r *http.Request) {
 	}
 	s.Throttle.Succeeded()
 	slog.Info("admin login", "user", user, "method", "local", "from", clientIP(r))
-	s.setSession(w, "local:"+cred.Username, cred.Username)
+	s.setSession(w, "local:"+cred.Username, cred.Username, true)
 	http.Redirect(w, r, "/", http.StatusSeeOther)
 }
 
+// apiAdmin authenticates a programmatic admin request: the normal session cookie, or HTTP Basic
+// against the break-glass credential for callers without a cookie jar (the README's curl).
+//
+// The cookie path keeps CSRF on anything that changes state, exactly like guard: a cookie is an
+// ambient credential. Basic auth is exempt — the password is supplied explicitly per request, so
+// there is nothing for a cross-site form to ride on — and a wrong guess pays the same throttle as
+// the login form, so this is no better a password oracle than that is.
+func (s *Server) apiAdmin(w http.ResponseWriter, r *http.Request) (subject string, ok bool) {
+	if sess := s.session(r); sess != nil {
+		if !sess.Admin {
+			http.Error(w, "that action needs an administrator account", http.StatusForbidden)
+			return "", false
+		}
+		if !safeMethod(r) && !s.csrfOK(r, sess) {
+			http.Error(w, "stale form — reload the page and try again", http.StatusForbidden)
+			return "", false
+		}
+		return sess.Subject, true
+	}
+	if user, pass, hasBasic := r.BasicAuth(); hasBasic {
+		if d := s.Throttle.Delay(); d > 0 {
+			time.Sleep(d)
+		}
+		if cred := s.Store.LocalAdmin(); cred != nil && cred.Verify(user, pass) {
+			s.Throttle.Succeeded()
+			return "local:" + user, true
+		}
+		s.Throttle.Failed()
+		slog.Info("admin api auth failed", "user", user, "from", clientIP(r))
+	}
+	w.Header().Set("WWW-Authenticate", `Basic realm="echolot-admin"`)
+	http.Error(w, "authentication required", http.StatusUnauthorized)
+	return "", false
+}
+
 // ---- OIDC -------------------------------------------------------------------------------
 
 func (s *Server) oidcAvailable() bool {
@@ -271,18 +365,14 @@ func (s *Server) oidcCallback(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "the identity token was not accepted", http.StatusForbidden)
 		return
 	}
-	if !s.OIDC.IsAdmin(claims) {
-		// Named explicitly: "you signed in but you are not an admin" is a different problem from
-		// "your password is wrong", and the group is the thing to go and check.
-		slog.Info("admin access denied: not in group", "account", claims.AccountID(),
-			"want_group", s.OIDC.Config().AdminGroup, "have", claims.Groups)
-		http.Error(w, fmt.Sprintf(
-			"Signed in as %s, but that account is not in the %q group, so it cannot administer "+
-				"this server.", claims.Display(), s.OIDC.Config().AdminGroup), http.StatusForbidden)
-		return
-	}
-	slog.Info("admin login", "account", claims.AccountID(), "method", "oidc", "from", clientIP(r))
-	s.setSession(w, claims.AccountID(), claims.Display())
+	// Authentication and authorisation are answered separately here. Someone who is not in the
+	// admin group has still proved who they are, and their own uploads are their business to
+	// manage — refusing them a session outright, as this used to, left a legitimate account with
+	// no way to see or delete the data it had sent.
+	admin := s.OIDC.IsAdmin(claims)
+	slog.Info("login", "account", claims.AccountID(), "method", "oidc", "admin", admin,
+		"from", clientIP(r))
+	s.setSession(w, claims.AccountID(), claims.Display(), admin)
 	http.Redirect(w, r, "/", http.StatusSeeOther)
 }
 

server/internal/adminui/enrolltokens_test.go

@@ -0,0 +1,88 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package adminui
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"echo-lot.app/server/internal/adminauth"
+)
+
+// tokenFixture wires just enough of the Server for the mint endpoint: a break-glass admin and
+// a stand-in EnrollLink (the real one belongs to the control server, injected the same way).
+func tokenFixture(t *testing.T) *Server {
+	t.Helper()
+	s, _, _, _ := fixture(t)
+	secret, err := s.Store.SessionSecret()
+	if err != nil {
+		t.Fatal(err)
+	}
+	s.Sessions = adminauth.NewSessions(secret, time.Hour)
+	s.Throttle = adminauth.NewThrottle()
+	cred, err := adminauth.NewCredential("admin", "a-long-test-password")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := s.Store.SetLocalAdmin(cred); err != nil {
+		t.Fatal(err)
+	}
+	s.EnrollLink = func(tok string) string { return "echolot://enroll?v=1&t=" + tok }
+	return s
+}
+
+func TestEnrollTokensAPISpecShape(t *testing.T) {
+	h := tokenFixture(t).Handler()
+
+	// No credentials → 401 with a challenge, never a token.
+	req := httptest.NewRequest("POST", "/admin/enroll-tokens?note=phone", nil)
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusUnauthorized || rec.Header().Get("WWW-Authenticate") == "" {
+		t.Fatalf("unauthenticated: code=%d", rec.Code)
+	}
+
+	// Wrong password → still 401.
+	req = httptest.NewRequest("POST", "/admin/enroll-tokens", nil)
+	req.SetBasicAuth("admin", "wrong")
+	rec = httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("bad password: code=%d, want 401", rec.Code)
+	}
+
+	// Basic + Accept: application/json → the §2.1 shape.
+	req = httptest.NewRequest("POST", "/admin/enroll-tokens?note=phone", nil)
+	req.SetBasicAuth("admin", "a-long-test-password")
+	req.Header.Set("Accept", "application/json")
+	rec = httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("mint: code=%d body=%s", rec.Code, rec.Body.String())
+	}
+	var body struct {
+		Token     string `json:"token"`
+		ExpiresS  int    `json:"expires_in_s"`
+		EnrollURI string `json:"enroll_uri"`
+	}
+	if err := json.Unmarshal(rec.Body.Bytes(), &body); err != nil {
+		t.Fatal(err)
+	}
+	if body.Token == "" || body.ExpiresS != 86400 || !strings.HasPrefix(body.EnrollURI, "echolot://enroll?") {
+		t.Fatalf("spec shape violated: %+v", body)
+	}
+
+	// Without Accept: the browser flow — redirect to the QR page, link in the query.
+	req = httptest.NewRequest("POST", "/admin/enroll-tokens", nil)
+	req.SetBasicAuth("admin", "a-long-test-password")
+	rec = httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusSeeOther || !strings.HasPrefix(rec.Header().Get("Location"), "/devices?link=") {
+		t.Fatalf("html flow: code=%d location=%q", rec.Code, rec.Header().Get("Location"))
+	}
+}

server/internal/adminui/pages.go

@@ -5,10 +5,12 @@ package adminui
 
 import (
 	"encoding/json"
+	"html/template"
 	"log/slog"
 	"net/http"
 	"net/url"
 	"sort"
+	"strings"
 	"time"
 
 	"echo-lot.app/server/internal/adminauth"
@@ -16,6 +18,46 @@ import (
 	"echo-lot.app/server/internal/store"
 )
 
+// visibleDevices returns the devices a session may see: everything for an administrator, and for
+// anyone else the devices linked to their own account.
+//
+// Every page goes through this rather than filtering for itself. Scoping applied per-page is
+// scoping that will be missing from the next page someone adds, and the failure is silent — a
+// listing that quietly shows other people's uploads looks exactly like one that does not.
+func (s *Server) visibleDevices(sess *adminauth.Session) []store.Device {
+	all := s.Store.Devices()
+	if sess.Admin {
+		return all
+	}
+	owned := make(map[string]bool)
+	for _, id := range s.Store.DeviceIDsForAccount(sess.Subject) {
+		owned[id] = true
+	}
+	out := make([]store.Device, 0, len(owned))
+	for _, d := range all {
+		if owned[d.ID] {
+			out = append(out, d)
+		}
+	}
+	return out
+}
+
+// mayTouchRun reports whether this session may read or delete a given run.
+//
+// Checked against the device list rather than against the run's own metadata, so an unlinked or
+// revoked device stops granting access the moment the link is gone.
+func (s *Server) mayTouchRun(sess *adminauth.Session, device string) bool {
+	if sess.Admin {
+		return true
+	}
+	for _, d := range s.visibleDevices(sess) {
+		if d.ID == device {
+			return true
+		}
+	}
+	return false
+}
+
 func (s *Server) loginForm(w http.ResponseWriter, r *http.Request) {
 	if s.session(r) != nil {
 		http.Redirect(w, r, "/", http.StatusSeeOther)
@@ -29,7 +71,7 @@ func (s *Server) loginForm(w http.ResponseWriter, r *http.Request) {
 }
 
 func (s *Server) dashboard(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
-	devices := s.Store.Devices()
+	devices := s.visibleDevices(sess)
 	linked := 0
 	for _, d := range devices {
 		if d.LinkedToAccount() {
@@ -37,9 +79,17 @@ func (s *Server) dashboard(w http.ResponseWriter, r *http.Request, sess *adminau
 		}
 	}
 	var selftest any
-	if s.SelfTest != nil {
+	// The self-test describes the server's own health, which is an operator's concern; a user
+	// looking at their uploads has no use for it and no ability to act on it.
+	if s.SelfTest != nil && sess.Admin {
 		selftest = s.SelfTest()
 	}
+	// Same reasoning for the dev relay, and one more: the rows carry a LAN address and a debug
+	// port, so they go no further than the account that runs the server.
+	var adb []adbRow
+	if sess.Admin {
+		adb = s.adbRows()
+	}
 	s.render(w, r, "dashboard", map[string]any{
 		"Session":      sess,
 		"CSRF":         s.csrfToken(sess),
@@ -47,7 +97,9 @@ func (s *Server) dashboard(w http.ResponseWriter, r *http.Request, sess *adminau
 		"Linked":       linked,
 		"Runs":         s.totalRuns(devices),
 		"SelfTest":     selftest,
+		"ADBEndpoints": adb,
 		"Version":      s.Version,
+		"Admin":        sess.Admin,
 	})
 }
 
@@ -63,7 +115,7 @@ func (s *Server) totalRuns(devices []store.Device) int {
 }
 
 func (s *Server) devices(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
-	devices := s.Store.Devices()
+	devices := s.visibleDevices(sess)
 	// Newest first: the device someone is looking for is almost always the one just enrolled.
 	sort.Slice(devices, func(i, j int) bool { return devices[i].Enrolled.After(devices[j].Enrolled) })
 
@@ -79,9 +131,22 @@ func (s *Server) devices(w http.ResponseWriter, r *http.Request, sess *adminauth
 		}
 		rows = append(rows, row{Device: d, Runs: n})
 	}
+	// html/template rewrites an href whose scheme it does not recognise to "#ZgotmplZ", so the
+	// enrollment link rendered as a dead anchor that did nothing when tapped — silently, since the
+	// markup looks fine and only the sanitised attribute gives it away.
+	//
+	// Marking it template.URL opts out of that sanitising, which is only safe because the shape is
+	// checked first: this value arrives in a query parameter, so without the check a crafted
+	// /devices?link=javascript:… would put a script URL straight into the page.
+	link := r.URL.Query().Get("link")
+	var href template.URL
+	if strings.HasPrefix(link, "echolot://enroll?") {
+		href = template.URL(link)
+	}
 	s.render(w, r, "devices", map[string]any{
 		"Session": sess, "CSRF": s.csrfToken(sess), "Rows": rows,
-		"Link": r.URL.Query().Get("link"),
+		// Rendered from the same validated value as the href, so a rejected link produces neither.
+		"Link": link, "LinkHref": href, "LinkQR": qrSVG(string(href)), "Admin": sess.Admin,
 	})
 }
 
@@ -109,6 +174,41 @@ func (s *Server) mintToken(w http.ResponseWriter, r *http.Request, sess *adminau
 	http.Redirect(w, r, "/devices?link="+url.QueryEscape(s.EnrollLink(tok)), http.StatusSeeOther)
 }
 
+// enrollTokensAPI is POST /admin/enroll-tokens, the endpoint the spec's §2.1 example names.
+// Content-negotiated: Accept: application/json gets the spec shape {token, expires_in_s,
+// enroll_uri}; anything else (a browser) gets the same redirect-to-QR flow as the form above,
+// so the one path serves both audiences.
+func (s *Server) enrollTokensAPI(w http.ResponseWriter, r *http.Request) {
+	subject, ok := s.apiAdmin(w, r)
+	if !ok {
+		return
+	}
+	note := r.URL.Query().Get("note")
+	if note == "" {
+		note = "admin-api"
+	}
+	const ttl = 24 * time.Hour
+	tok, err := s.Store.NewEnrollToken(ttl, note)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	slog.Info("enrolment token minted", "by", subject, "note", note)
+	if !strings.Contains(r.Header.Get("Accept"), "application/json") {
+		http.Redirect(w, r, "/devices?link="+url.QueryEscape(s.EnrollLink(tok)), http.StatusSeeOther)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	// The whole link, not the bare token (§2.1): the server is the only party holding URL, pin
+	// and token at once, and a hand-assembled pin wrong by one character fails as an inscrutable
+	// TLS error later rather than loudly here.
+	_ = json.NewEncoder(w).Encode(map[string]any{
+		"token":        tok,
+		"expires_in_s": int(ttl.Seconds()),
+		"enroll_uri":   s.EnrollLink(tok),
+	})
+}
+
 // EnrollLink is supplied by the caller so this package does not need the control server's pin.
 var _ = 0
 
@@ -118,7 +218,7 @@ func (s *Server) runsList(w http.ResponseWriter, r *http.Request, sess *adminaut
 		DeviceName string
 	}
 	var rows []row
-	for _, d := range s.Store.Devices() {
+	for _, d := range s.visibleDevices(sess) {
 		if s.Runs == nil {
 			break
 		}
@@ -134,10 +234,18 @@ func (s *Server) runsList(w http.ResponseWriter, r *http.Request, sess *adminaut
 	if len(rows) > 200 {
 		rows = rows[:200] // a page, not the archive; the count is on the dashboard
 	}
-	s.render(w, r, "runs", map[string]any{"Session": sess, "CSRF": s.csrfToken(sess), "Rows": rows})
+	s.render(w, r, "runs", map[string]any{
+		"Session": sess, "CSRF": s.csrfToken(sess), "Rows": rows, "Admin": sess.Admin,
+	})
 }
 
 func (s *Server) runView(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
+	// 404 rather than 403 for someone else's run: a distinguishable "you may not see this" tells
+	// an unauthorised caller that the run exists, which is itself something they should not learn.
+	if !s.mayTouchRun(sess, r.PathValue("device")) {
+		http.NotFound(w, r)
+		return
+	}
 	body, err := s.Runs.Get(r.PathValue("device"), r.PathValue("id"))
 	if err != nil {
 		http.NotFound(w, r)
@@ -151,7 +259,7 @@ func (s *Server) runView(w http.ResponseWriter, r *http.Request, sess *adminauth
 		out = body
 	}
 	s.render(w, r, "run", map[string]any{
-		"Session": sess, "CSRF": s.csrfToken(sess),
+		"Session": sess, "CSRF": s.csrfToken(sess), "Admin": sess.Admin,
 		"Device": r.PathValue("device"), "ID": r.PathValue("id"),
 		"JSON": string(out),
 	})
@@ -159,6 +267,10 @@ func (s *Server) runView(w http.ResponseWriter, r *http.Request, sess *adminauth
 
 func (s *Server) runDelete(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
 	device, id := r.PathValue("device"), r.PathValue("id")
+	if !s.mayTouchRun(sess, device) {
+		http.NotFound(w, r)
+		return
+	}
 	if err := s.Runs.Delete(device, id); err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return

server/internal/adminui/qr.go

@@ -0,0 +1,58 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package adminui
+
+import (
+	"fmt"
+	"html/template"
+	"strings"
+
+	qrcode "github.com/skip2/go-qrcode"
+)
+
+// qrSVG renders text as an inline SVG QR code, or empty if it will not encode.
+//
+// Inline SVG rather than a PNG data: URI because the page's CSP is `default-src 'none'` and means
+// it. A data: image would need img-src opened up; markup needs nothing, and the QR is generated
+// here from a boolean matrix, so nothing a user supplied reaches the output.
+//
+// Drawn as one path rather than a rect per module: a link of this length encodes to roughly 60x60
+// modules, and two thousand elements is a lot of DOM for a picture of a square.
+func qrSVG(text string) template.HTML {
+	if text == "" {
+		return ""
+	}
+	// Medium recovery: a phone camera reading a screen has no dirt or creases to survive, and
+	// lower recovery keeps the module count down, which keeps it scannable on a small display.
+	q, err := qrcode.New(text, qrcode.Medium)
+	if err != nil {
+		return "" // too long to encode; the link text below it still works
+	}
+	bitmap := q.Bitmap()
+	n := len(bitmap)
+	if n == 0 {
+		return ""
+	}
+
+	var path strings.Builder
+	for y, row := range bitmap {
+		for x, dark := range row {
+			if dark {
+				fmt.Fprintf(&path, "M%d %dh1v1h-1z", x, y)
+			}
+		}
+	}
+
+	// A quiet zone is part of the spec, not decoration: without it a scanner cannot find the
+	// symbol's edges against whatever is next to it on the page.
+	var out strings.Builder
+	fmt.Fprintf(&out,
+		`<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 %d %d" `+
+			`width="240" height="240" shape-rendering="crispEdges" role="img" `+
+			`aria-label="Enrolment link as a QR code">`+
+			`<rect width="%d" height="%d" fill="#fff"/>`+
+			`<path d="%s" fill="#000"/></svg>`,
+		n, n, n, n, path.String())
+	return template.HTML(out.String())
+}

server/internal/adminui/qr_test.go

@@ -0,0 +1,24 @@
+package adminui
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestQrSVGEncodesAnEnrolmentLink(t *testing.T) {
+	link := "echolot://enroll?v=1&u=https%3A%2F%2Ffmr.echo-lot.app&p=pin-sha256%3AzRV9qkiLnRexAeh4RrSfJzbPWO%2BU%2F2Oj2%2FNVM%2FKfXlg%3D&t=20e6ccaa2a028dc0aab16442c258d1b8eadb5794682905fe"
+	out := string(qrSVG(link))
+	if !strings.HasPrefix(out, "<svg") || !strings.Contains(out, "<path d=\"M") {
+		t.Fatalf("expected an svg with a path, got %.80q", out)
+	}
+	// A quiet zone is part of the symbol; without it scanners cannot find its edges.
+	if !strings.Contains(out, `fill="#fff"`) {
+		t.Error("no light background rendered")
+	}
+}
+
+func TestQrSVGEmptyForNoLink(t *testing.T) {
+	if qrSVG("") != "" {
+		t.Error("no link should render no code")
+	}
+}

server/internal/adminui/render.go

@@ -8,12 +8,55 @@ import (
 	"html/template"
 	"log/slog"
 	"net/http"
+	"strconv"
+	"strings"
 )
 
 // Templates are parsed once at start. html/template escapes by context, which is what makes it
 // safe to render device names and finding text that ultimately arrived over a network.
 var tpl = template.Must(template.New("base").Funcs(template.FuncMap{
 	"kb": func(n int64) int64 { return n / 1024 },
+	// verdictClass keeps an uploaded string out of the class attribute. The verdict arrives inside
+	// a document a device sent us, so interpolating it into markup would be trusting a stranger's
+	// text with a place in the stylesheet; mapping through a fixed set costs nothing and closes it.
+	"verdictClass": func(v string) string {
+		switch strings.ToLower(v) {
+		case "green", "yellow", "red", "inconclusive":
+			return "v-" + strings.ToLower(v)
+		default:
+			return "v-unknown"
+		}
+	},
+	// ago renders an age the way someone says it out loud. The dev relay reports a port that
+	// rotates every few minutes, so "4 m ago" is the entire question a reader has about a row.
+	"ago": func(seconds int) string {
+		switch {
+		case seconds < 45:
+			return "just now"
+		case seconds < 90*60:
+			return strconv.Itoa((seconds+30)/60) + " min ago"
+		case seconds < 48*3600:
+			return strconv.Itoa((seconds+1800)/3600) + " h ago"
+		default:
+			return strconv.Itoa(seconds/86400) + " d ago"
+		}
+	},
+	// verdictLabel says what the light means rather than what it is called. "yellow" is a colour;
+	// "worth a look" is a finding, and the reader is here to act on it.
+	"verdictLabel": func(v string) string {
+		switch strings.ToLower(v) {
+		case "green":
+			return "clean"
+		case "yellow":
+			return "worth a look"
+		case "red":
+			return "faults found"
+		case "inconclusive":
+			return "inconclusive"
+		default:
+			return "not recorded"
+		}
+	},
 }).Parse(baseHTML))
 
 func (s *Server) render(w http.ResponseWriter, r *http.Request, page string, data map[string]any) {
@@ -33,133 +76,380 @@ func (s *Server) render(w http.ResponseWriter, r *http.Request, page string, dat
 	_, _ = buf.WriteTo(w)
 }
 
+// The visual language is an echo sounder's, which is what the name means: an instrument that emits
+// a ping and reads what comes back. That gives the palette (the colours of a water column rather
+// than a neutral near-black), the type (machine-set, because an instrument's readings are), and
+// the one piece of real ornament — a trace of returns across time on the runs page.
+//
+// No web fonts: the CSP forbids loading anything, and shipping font files with a single Go binary
+// would trade the property that makes this server pleasant to run for a typeface. So the character
+// has to come from treatment — tracking, case, scale, rules — rather than from novel letterforms.
+//
+// Tables become stacked records below 46rem rather than scrolling sideways. That is not a fallback:
+// a sounding log prints as label-and-value pairs, and on a phone that form is easier to read than
+// any table, so the mobile layout is the more faithful one of the two.
 const baseHTML = `<!doctype html>
 <html lang="en"><head><meta charset="utf-8">
 <meta name="viewport" content="width=device-width,initial-scale=1">
 <title>Echolot &mdash; {{.Page}}</title>
 <style>
- :root{color-scheme:dark}
- body{font:15px/1.5 system-ui,sans-serif;margin:0;background:#14161a;color:#e6e6e6}
- header{display:flex;gap:1.2rem;align-items:baseline;padding:.8rem 1.2rem;background:#1c1f25;border-bottom:1px solid #2b2f36}
- header h1{font-size:1.1rem;margin:0;font-weight:600}
- header nav a{color:#9ecbff;text-decoration:none;margin-right:1rem}
- header .who{margin-left:auto;color:#9aa3ad;font-size:.9rem}
- main{padding:1.2rem;max-width:70rem}
- table{border-collapse:collapse;width:100%;margin:.6rem 0}
- th,td{text-align:left;padding:.45rem .6rem;border-bottom:1px solid #2b2f36;vertical-align:top}
- th{color:#9aa3ad;font-weight:500;font-size:.85rem}
- code,pre{font-family:ui-monospace,monospace;font-size:.85rem}
- pre{background:#0f1114;padding:.8rem;border-radius:6px;overflow:auto;max-height:34rem}
- .card{background:#1c1f25;border:1px solid #2b2f36;border-radius:8px;padding:1rem;margin:.8rem 0}
- .grid{display:flex;gap:1rem;flex-wrap:wrap}
- .stat{background:#1c1f25;border:1px solid #2b2f36;border-radius:8px;padding:.8rem 1.2rem;min-width:8rem}
- .stat b{display:block;font-size:1.6rem;font-weight:600}
- .stat span{color:#9aa3ad;font-size:.85rem}
- button{font:inherit;background:#2d6cdf;color:#fff;border:0;border-radius:6px;padding:.4rem .8rem;cursor:pointer}
- button.danger{background:#8b2f2f}
- button.plain{background:#3a3f47}
- input{font:inherit;background:#0f1114;color:#e6e6e6;border:1px solid #2b2f36;border-radius:6px;padding:.4rem .6rem}
- .err{background:#3a1f1f;border:1px solid #7a3b3b;padding:.6rem .8rem;border-radius:6px}
- .muted{color:#9aa3ad}
+ :root{
+   --abyss:#071419; --hull:#0d2028; --raise:#122a34; --rule:#17323d;
+   --ink:#dce8ea; --dim:#7d97a1; --trace:#6fc9b4;
+   --green:#57ad82; --amber:#cf9b3c; --red:#c25757; --slate:#62767f;
+   --mono:ui-monospace,"SF Mono","IBM Plex Mono","JetBrains Mono",Menlo,Consolas,monospace;
+   --prose:system-ui,-apple-system,"Segoe UI",sans-serif;
+   color-scheme:dark;
+ }
+ *{box-sizing:border-box}
+ body{margin:0;background:var(--abyss);color:var(--ink);
+      font:400 15px/1.55 var(--prose);-webkit-text-size-adjust:100%}
+
+ /* ---- masthead ------------------------------------------------------------------------ */
+ /* Wraps rather than overflows: a rigid row pushes the account and its sign-out button past
+    the edge of a phone screen, where they cannot be reached at all. */
+ .top{display:flex;flex-wrap:wrap;align-items:center;gap:.5rem 1.4rem;
+      padding:.85rem 1.1rem;background:var(--hull);border-bottom:1px solid var(--rule)}
+ .mark{font:600 .95rem/1 var(--mono);letter-spacing:.02em;margin:0;color:var(--ink)}
+ .mark span{color:var(--trace)}
+ .top nav{display:flex;flex-wrap:wrap;gap:.15rem .9rem}
+ .top nav a{font:500 .82rem/1 var(--mono);letter-spacing:.06em;color:var(--dim);
+            text-decoration:none;padding:.35rem 0;border-bottom:1px solid transparent}
+ .top nav a:hover{color:var(--ink)}
+ .top nav a[aria-current]{color:var(--trace);border-bottom-color:var(--trace)}
+ .who{margin-left:auto;display:flex;align-items:center;gap:.7rem;flex-wrap:wrap;
+      font:.78rem/1.3 var(--mono);color:var(--dim)}
+
+ main{padding:1.1rem;max-width:64rem}
+
+ /* ---- headings: a graduation mark, like a depth scale ------------------------------- */
+ h2{font:500 1.05rem/1.2 var(--mono);letter-spacing:-.01em;margin:1.4rem 0 .2rem;
+    padding-left:.7rem;border-left:2px solid var(--trace)}
+ h2:first-child{margin-top:0}
+ h3{font:500 .8rem/1 var(--mono);letter-spacing:.14em;text-transform:uppercase;
+    color:var(--dim);margin:0 0 .7rem}
+ .lede{color:var(--dim);font-size:.9rem;margin:.5rem 0 1rem;max-width:46rem}
+
+ /* ---- readout: how an instrument prints a value ------------------------------------- */
+ .readout{list-style:none;margin:0;padding:0}
+ .readout li{display:flex;align-items:baseline;gap:.5rem;padding:.3rem 0;
+             font:.85rem/1.4 var(--mono)}
+ .readout .k{color:var(--dim);white-space:nowrap}
+ /* The dotted leader is how a sounding log runs a label out to its value. It is also the thing
+    that lets a label and a number sit on one line at any width without a table. */
+ .readout .lead{flex:1 1 auto;min-width:1.5rem;align-self:center;height:1px;
+                background:repeating-linear-gradient(90deg,var(--rule) 0 2px,transparent 2px 5px)}
+ .readout .v{color:var(--ink);text-align:right;overflow-wrap:anywhere}
+
+ /* ---- the trace: one bar per run, oldest to newest ---------------------------------- */
+ /* The signature, and the only ornament here: an echo sounder draws returns against time, and
+    so does this. Rows arrive newest-first, so the strip is reversed in CSS rather than in Go. */
+ .trace{display:flex;flex-direction:row-reverse;justify-content:flex-end;align-items:flex-end;gap:2px;
+        height:3rem;padding:.7rem .8rem;background:var(--hull);
+        border:1px solid var(--rule);border-radius:3px;overflow:hidden}
+ .trace i{flex:1 1 3px;min-width:2px;max-width:9px;border-radius:1px;opacity:.9}
+ .trace .v-green{height:35%;background:var(--green)}
+ .trace .v-yellow{height:65%;background:var(--amber)}
+ .trace .v-red{height:100%;background:var(--red)}
+ .trace .v-inconclusive{height:22%;background:var(--slate)}
+ .trace .v-unknown{height:12%;background:var(--rule)}
+ .trace-key{display:flex;flex-wrap:wrap;gap:.3rem .9rem;margin:.45rem 0 0;
+            font:.72rem/1 var(--mono);letter-spacing:.05em;color:var(--dim)}
+ .trace-key b{font-weight:400;color:var(--dim)}
+ .trace-key em{font-style:normal;display:inline-block;width:.5rem;height:.5rem;
+               border-radius:1px;margin-right:.35rem;vertical-align:baseline;background:var(--rule)}
+ .trace-key em.v-green{background:var(--green)}
+ .trace-key em.v-yellow{background:var(--amber)}
+ .trace-key em.v-red{background:var(--red)}
+ .trace-key em.v-inconclusive{background:var(--slate)}
+
+ /* ---- records: tables that stack on a phone ----------------------------------------- */
+ .rec{border:1px solid var(--rule);border-radius:3px;background:var(--hull);
+      padding:.75rem .85rem;margin:.5rem 0}
+ .rec-head{display:flex;flex-wrap:wrap;align-items:baseline;gap:.5rem;
+           font:.85rem/1.3 var(--mono);margin-bottom:.35rem}
+ .rec-head .id{overflow-wrap:anywhere;color:var(--ink)}
+ .rec form{margin-top:.6rem}
+ /* Why a check matters is a sentence, so it is set as one — full width under the row rather
+    than squeezed into a column, where it would wrap to a ribbon two words wide. */
+ .why{font:.85rem/1.5 var(--prose);color:var(--dim);margin-top:.45rem;max-width:52rem}
+ .tag{font:.68rem/1 var(--mono);letter-spacing:.1em;text-transform:uppercase;
+      padding:.24rem .45rem;border-radius:2px;border:1px solid currentColor;white-space:nowrap}
+ .v-green{color:var(--green)} .v-yellow{color:var(--amber)}
+ .v-red{color:var(--red)} .v-inconclusive{color:var(--slate)} .v-unknown{color:var(--dim)}
+
+ /* ---- panels, controls, states ------------------------------------------------------ */
+ .narrow{max-width:27rem}
+ .panel{background:var(--hull);border:1px solid var(--rule);border-radius:3px;
+        padding:.95rem 1rem;margin:.9rem 0;min-width:0}
+ /* White plate behind the code: a QR needs the light modules to actually be light, and this
+    page is dark. */
+ .qr{display:inline-block;background:#fff;padding:8px;border-radius:4px;margin:.2rem 0;line-height:0}
+ .qr svg{display:block;width:min(240px,60vw);height:auto}
+ .empty{border:1px dashed var(--rule);border-radius:3px;padding:1.4rem 1rem;
+        color:var(--dim);font-size:.9rem}
+ code,pre,.mono{font-family:var(--mono);font-size:.82rem}
+ code{overflow-wrap:anywhere;color:var(--trace)}
+ pre{background:#040d11;border:1px solid var(--rule);border-radius:3px;padding:.8rem;
+     overflow:auto;max-height:32rem;max-width:100%;color:var(--ink)}
+ a{color:var(--trace)}
+ button{font:500 .82rem/1 var(--mono);letter-spacing:.05em;background:var(--trace);
+        color:#04181a;border:0;border-radius:3px;padding:.55rem .9rem;cursor:pointer}
+ .btn{display:inline-block;font:500 .82rem/1 var(--mono);letter-spacing:.05em;
+      background:var(--trace);color:#04181a;border-radius:3px;padding:.55rem .9rem;
+      text-decoration:none}
+ button.plain{background:transparent;color:var(--dim);border:1px solid var(--rule)}
+ button.danger{background:transparent;color:var(--red);border:1px solid var(--red)}
+ button:hover{filter:brightness(1.08)}
+ input{font:.9rem var(--mono);background:#040d11;color:var(--ink);border:1px solid var(--rule);
+       border-radius:3px;padding:.55rem .6rem;max-width:100%;width:100%}
+ label{display:block;font:.72rem/1 var(--mono);letter-spacing:.12em;text-transform:uppercase;
+       color:var(--dim);margin:.9rem 0 .3rem}
+ .err{border:1px solid var(--red);color:var(--ink);background:rgba(194,87,87,.09);
+      padding:.6rem .75rem;border-radius:3px;font-size:.9rem}
+ .muted{color:var(--dim)}
  form.inline{display:inline}
+ :focus-visible{outline:2px solid var(--trace);outline-offset:2px}
+ @media (prefers-reduced-motion:reduce){*{transition:none!important;animation:none!important}}
+
+ /* ---- above 46rem the records line up in columns ------------------------------------ */
+ @media (min-width:46rem){
+   .top{padding:.85rem 1.6rem}
+   main{padding:1.6rem}
+   .recs{margin:.8rem 0}
+   /* Every row shares one grid, so the columns agree across rows without a header or a table. */
+   .rec{display:grid;grid-template-columns:minmax(12.5rem,18rem) minmax(0,1fr) auto;gap:.35rem 1.4rem;
+        align-items:baseline;background:none;border:0;border-bottom:1px solid var(--rule);
+        border-radius:0;padding:.6rem 0;margin:0}
+   .rec-head{margin:0;flex-direction:column;align-items:flex-start;gap:.3rem}
+   .rec form{margin:0}
+   /* Widths follow the content: a device name needs room, a finding count does not. */
+   .rec .readout{display:grid;grid-template-columns:1.7fr .9fr .9fr 1.1fr;gap:.15rem 1.2rem}
+   .rec .readout li{padding:0}
+   .rec .readout .lead{display:none}
+   .rec .readout .v{text-align:left}
+   .open{white-space:nowrap}
+   /* Spans the full row: the sentence is the useful part, not a fourth column. */
+   .why{grid-column:1/-1;margin-top:.1rem}
+ }
 </style></head><body>
+<header class="top">
+  <h1 class="mark">echo<span>lot</span></h1>
   {{if ne .Page "login"}}
-<header>
-  <h1>Echolot</h1>
-  <nav><a href="/">Overview</a><a href="/devices">Devices</a><a href="/runs">Runs</a></nav>
-  <span class="who">{{.Session.Display}}
+  <nav>
+    <a href="/"{{if eq .Page "dashboard"}} aria-current="page"{{end}}>overview</a>
+    <a href="/devices"{{if eq .Page "devices"}} aria-current="page"{{end}}>devices</a>
+    <a href="/runs"{{if eq .Page "runs"}} aria-current="page"{{end}}>runs</a>
+  </nav>
+  <span class="who">{{.Session.Display}}{{if not .Session.Admin}} &middot; your account{{end}}
     <form method="post" action="/logout" class="inline"><button class="plain">Sign out</button></form>
   </span>
-</header>
   {{end}}
+</header>
 <main>
 
 {{if eq .Page "login"}}
   <h2>Sign in</h2>
-  {{with .Error}}<p class="err">{{.}}</p>{{end}}
+  <p class="lede">This server keeps the measurements your devices have uploaded.</p>
   {{if .OIDC}}
-    <p><a href="/auth/start"><button>Sign in with your identity provider</button></a></p>
-    <p class="muted">or use the break-glass account:</p>
+    <p><a class="btn" href="/auth/start">Sign in with your identity provider</a></p>
   {{end}}
   {{if .LocalSet}}
-    <form method="post" action="/login" class="card">
-      <p><label>Username<br><input name="username" value="{{.AdminUser}}" autocomplete="username"></label></p>
-      <p><label>Password<br><input name="password" type="password" autocomplete="current-password"></label></p>
+    <form method="post" action="/login" class="panel narrow">
+      <h3>Break-glass account</h3>
+      <label for="u">Username</label>
+      <input id="u" name="username" autocomplete="username" value="{{.AdminUser}}">
+      <label for="p">Password</label>
+      <input id="p" name="password" type="password" autocomplete="current-password">
       <p><button>Sign in</button></p>
     </form>
   {{else}}
-    <p class="err">No break-glass admin is set. Run
-      <code>echolot-server --set-admin-password</code> on the host.</p>
+    <p class="err">No break-glass account is set. Run
+      <code>echolot-server --set-admin-password</code> on the host to create one.</p>
   {{end}}
 
 {{else if eq .Page "dashboard"}}
-  <div class="grid">
-    <div class="stat"><b>{{.Devices}}</b><span>devices</span></div>
-    <div class="stat"><b>{{.Linked}}</b><span>signed in</span></div>
-    <div class="stat"><b>{{.Runs}}</b><span>stored runs</span></div>
-  </div>
-  <div class="card">
-    <h3>Server</h3>
-    <p class="muted">version {{.Version}}</p>
-    {{with .SelfTest}}<pre>{{printf "%+v" .}}</pre>{{end}}
-  </div>
-
-{{else if eq .Page "devices"}}
-  <h2>Devices</h2>
-  {{with .Link}}
-  <div class="card">
-    <p><b>Enrolment link</b> &mdash; single use, valid 24 hours. Treat it like a password until spent.</p>
-    <p><code>{{.}}</code></p>
-    <p class="muted">On a device with adb:<br>
-      <code>adb shell am start -a android.intent.action.VIEW -d "{{.}}"</code></p>
+  <h2>{{if .Admin}}This server{{else}}Your account{{end}}</h2>
+  <ul class="readout panel">
+    <li><span class="k">{{if .Admin}}devices enrolled{{else}}your devices{{end}}</span>
+        <span class="lead"></span><span class="v">{{.Devices}}</span></li>
+    {{if .Admin}}
+    <li><span class="k">linked to an account</span>
+        <span class="lead"></span><span class="v">{{.Linked}}</span></li>
+    {{end}}
+    <li><span class="k">{{if .Admin}}runs stored{{else}}your runs{{end}}</span>
+        <span class="lead"></span><span class="v">{{.Runs}}</span></li>
+    {{if .Admin}}
+    <li><span class="k">server version</span>
+        <span class="lead"></span><span class="v">{{.Version}}</span></li>
+    {{end}}
+  </ul>
+  {{if not .Admin}}
+  <div class="panel">
+    <p>You can see every device you have signed in on, read everything they have uploaded, and
+      delete any of it.</p>
+    <p class="muted">Enrolling devices, revoking them, and reading other people's uploads need an
+      administrator account.</p>
   </div>
   {{end}}
+  {{with .SelfTest}}
+  <h2>Self-test</h2>
+  <p class="lede">What this server can measure from where it stands, checked at startup. A
+    capability missing here is missing from every run this server takes part in &mdash; so a
+    client asking for that measurement gets nothing, rather than a wrong answer.</p>
+  <ul class="readout panel">
+    <li><span class="k">kernel settings</span><span class="lead"></span>
+      <span class="v {{if .SysctlOK}}v-green{{else}}v-yellow{{end}}">{{if .SysctlOK}}as needed{{else}}need attention{{end}}</span></li>
+    <li><span class="k">egress path MTU</span><span class="lead"></span>
+      <span class="v {{if .MTUOK}}v-green{{else}}v-yellow{{end}}">{{if .MTUOK}}full 1500{{else}}reduced{{end}}</span></li>
+  </ul>
+  {{if .Sysctls}}
+  <h3>Kernel settings</h3>
+  <div class="recs">
+  {{range .Sysctls}}
+    <div class="rec">
+      <div class="rec-head"><span class="id">{{.Name}}</span>
+        <span class="tag {{if eq .Severity "ok"}}v-green{{else}}v-yellow{{end}}">{{.Severity}}</span></div>
+      <ul class="readout">
+        <li><span class="k">found</span><span class="lead"></span><span class="v">{{.Got}}</span></li>
+        <li><span class="k">wanted</span><span class="lead"></span><span class="v">{{.Want}}</span></li>
+      </ul>
+      <div class="why">{{.Why}}</div>
+    </div>
+  {{end}}
+  </div>
+  {{end}}
+  {{if .EgressMTU}}
+  <h3>Egress path MTU</h3>
+  <div class="recs">
+  {{range .EgressMTU}}
+    <div class="rec">
+      <div class="rec-head"><span class="id">{{.Target}}</span>
+        <span class="tag {{if .FullMTU}}v-green{{else}}v-yellow{{end}}">{{if .FullMTU}}full{{else}}reduced{{end}}</span></div>
+      <ul class="readout">
+        <li><span class="k">discovered</span><span class="lead"></span>
+          <span class="v">{{if .DiscoveredMTU}}{{.DiscoveredMTU}} bytes{{else}}not measured{{end}}</span></li>
+      </ul>
+      {{with .Err}}<div class="why">{{.}}</div>{{end}}
+    </div>
+  {{end}}
+  </div>
+  {{end}}
+  {{end}}
+  {{with .ADBEndpoints}}
+  <h2>Dev relay</h2>
+  <p class="lede">Wireless-debug endpoints reported by Echolot instances on a test network. mDNS
+    does not cross subnets, so a device on that network relays adbd&rsquo;s rotating port here for
+    a developer sitting elsewhere. Nothing here is a measurement, and the entries expire &mdash;
+    a port older than a few minutes has probably already rotated.</p>
+  <div class="recs">
+  {{range .}}
+    <div class="rec">
+      <div class="rec-head">
+        <span class="id">{{if .DeviceName}}{{.DeviceName}}{{else}}{{.Device}}{{end}}</span>
+        <span class="tag v-unknown">{{ago .AgeS}}</span>
+      </div>
+      <ul class="readout">
+        <li><span class="k">adb connect</span><span class="lead"></span>
+            <span class="v">{{.Host}}:{{.Port}}</span></li>
+        <li><span class="k">device</span><span class="lead"></span><span class="v">{{.Device}}</span></li>
+        <li><span class="k">reported from</span><span class="lead"></span>
+            <span class="v">{{if .SourceIP}}{{.SourceIP}}{{else}}&mdash;{{end}}</span></li>
+      </ul>
+      {{with .Note}}<div class="why">{{.}}</div>{{end}}
+    </div>
+  {{end}}
+  </div>
+  {{end}}
+
+{{else if eq .Page "devices"}}
+  <h2>{{if .Admin}}Devices{{else}}Your devices{{end}}</h2>
+  {{with .Link}}
+  <div class="panel">
+    <h3>Enrolment link</h3>
+    <p class="lede">Single use, valid 24 hours. Treat it like a password until it is spent.</p>
+    <!-- On the phone being enrolled this is the whole procedure: the scheme is registered by the
+         app, so following the link hands it the token directly. Copying a 200-character string
+         between two devices is the step that goes wrong, and it does not have to happen at all. -->
+    {{with $.LinkHref}}<p><a class="btn" href="{{.}}">Open in the Echolot app</a></p>{{end}}
+    <p class="muted">Works on the phone you are enrolling. From another device, scan this:</p>
+    {{with $.LinkQR}}<div class="qr">{{.}}</div>{{end}}
+    <p class="muted">Or copy the link into the app's enrolment field, or deliver it over adb.</p>
+    <p><code>{{.}}</code></p>
+    <p class="muted mono">adb shell am start -a android.intent.action.VIEW -d "{{.}}"</p>
+  </div>
+  {{end}}
+  {{if .Admin}}
   <form method="post" action="/enroll-tokens">
     <input type="hidden" name="csrf" value="{{.CSRF}}">
     <button>Create enrolment link</button>
   </form>
-  <table>
-    <tr><th>Device</th><th>Name</th><th>Account</th><th>Enrolled</th><th>Runs</th><th></th></tr>
-    {{range .Rows}}
-    <tr>
-      <td><code>{{.ID}}</code></td>
-      <td>{{if .Name}}{{.Name}}{{else}}<span class="muted">&mdash;</span>{{end}}</td>
-      <td>{{if .LinkedToAccount}}{{.AccountName}}{{else}}<span class="muted">not signed in</span>{{end}}</td>
-      <td>{{.Enrolled.Format "2006-01-02 15:04"}}</td>
-      <td>{{.Runs}}</td>
-      <td><form method="post" action="/devices/{{.ID}}/revoke" class="inline">
-        <input type="hidden" name="csrf" value="{{$.CSRF}}">
-        <button class="danger">Revoke</button></form></td>
-    </tr>
-    {{else}}
-    <tr><td colspan="6" class="muted">No devices enrolled.</td></tr>
   {{end}}
-  </table>
+  {{if .Rows}}<div class="recs">
+  {{range .Rows}}
+    <div class="rec">
+      <div class="rec-head">
+        <span class="id">{{if .Name}}{{.Name}}{{else}}{{.ID}}{{end}}</span>
+        {{if .LinkedToAccount}}<span class="tag v-green">{{.AccountName}}</span>
+        {{else}}<span class="tag v-unknown">no account</span>{{end}}
+      </div>
+      <ul class="readout">
+        <li><span class="k">device</span><span class="lead"></span><span class="v">{{.ID}}</span></li>
+        <li><span class="k">enrolled</span><span class="lead"></span>
+            <span class="v">{{.Enrolled.Format "2006-01-02 15:04"}}</span></li>
+        <li><span class="k">runs</span><span class="lead"></span><span class="v">{{.Runs}}</span></li>
+      </ul>
+      {{if $.Admin}}
+      <form method="post" action="/devices/{{.ID}}/revoke">
+        <input type="hidden" name="csrf" value="{{$.CSRF}}">
+        <button class="danger">Revoke</button>
+      </form>
+      {{end}}
+    </div>
+  {{end}}
+  </div>{{else}}
+  <p class="empty">{{if .Admin}}No devices yet. Create an enrolment link and open it on the phone
+    you want to measure from.{{else}}No devices yet. Sign in from the Echolot app on your phone to
+    link one to this account.{{end}}</p>
+  {{end}}
 
 {{else if eq .Page "runs"}}
-  <h2>Uploaded runs</h2>
-  <p class="muted">Shown exactly as uploaded, at the privacy level the uploader chose. Nothing
-    here can un-redact a run.</p>
-  <table>
-    <tr><th>Uploaded</th><th>Device</th><th>Verdict</th><th>Findings</th><th>Size</th><th>Level</th><th></th></tr>
+  <h2>{{if .Admin}}Uploaded runs{{else}}Your uploaded runs{{end}}</h2>
+  <p class="lede">Each run is shown exactly as it arrived, at the privacy level its uploader chose.
+    Nothing here can un-redact one.</p>
+  {{if .Rows}}
+  <div class="trace">{{range .Rows}}<i class="{{verdictClass .Verdict}}"></i>{{end}}</div>
+  <p class="trace-key"><b>oldest &rarr; newest</b>
+    <b><em class="v-green"></em>clean</b>
+    <b><em class="v-yellow"></em>worth a look</b>
+    <b><em class="v-red"></em>faults</b>
+    <b><em class="v-inconclusive"></em>inconclusive</b></p>
+  {{end}}
+  {{if .Rows}}<div class="recs">
   {{range .Rows}}
-    <tr>
-      <td>{{.UploadedAt.Format "2006-01-02 15:04"}}</td>
-      <td>{{.DeviceName}}</td>
-      <td>{{if .Verdict}}{{.Verdict}}{{else}}<span class="muted">&mdash;</span>{{end}}</td>
-      <td>{{.FindingCount}}</td>
-      <td>{{kb .SizeBytes}} kB</td>
-      <td>{{.Anonymization}}</td>
-      <td><a href="/runs/{{.DeviceID}}/{{.ID}}">open</a></td>
-    </tr>
-    {{else}}
-    <tr><td colspan="7" class="muted">Nothing uploaded yet.</td></tr>
+    <div class="rec">
+      <div class="rec-head">
+        <span class="id">{{.UploadedAt.Format "2006-01-02 15:04"}}</span>
+        <span class="tag {{verdictClass .Verdict}}">{{verdictLabel .Verdict}}</span>
+      </div>
+      <ul class="readout">
+        <li><span class="k">device</span><span class="lead"></span><span class="v">{{.DeviceName}}</span></li>
+        <li><span class="k">findings</span><span class="lead"></span><span class="v">{{.FindingCount}}</span></li>
+        <li><span class="k">size</span><span class="lead"></span><span class="v">{{kb .SizeBytes}} kB</span></li>
+        <li><span class="k">privacy</span><span class="lead"></span><span class="v">{{.Anonymization}}</span></li>
+      </ul>
+      <div class="open"><a href="/runs/{{.DeviceID}}/{{.ID}}">Open run</a></div>
+    </div>
+  {{end}}
+  </div>{{else}}
+  <p class="empty">Nothing uploaded yet. Take a measurement in the app and upload it; it will
+    appear here.</p>
   {{end}}
-  </table>
 
 {{else if eq .Page "run"}}
   <h2>Run {{.ID}}</h2>
-  <form method="post" action="/runs/{{.Device}}/{{.ID}}/delete" class="inline">
+  <p class="lede">The document as stored, indented for reading. Nothing has been added or removed.</p>
+  <form method="post" action="/runs/{{.Device}}/{{.ID}}/delete">
     <input type="hidden" name="csrf" value="{{.CSRF}}">
     <button class="danger">Delete this run</button>
   </form>

server/internal/adminui/scope_test.go

@@ -0,0 +1,119 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package adminui
+
+import (
+	"testing"
+	"time"
+
+	"echo-lot.app/server/internal/adminauth"
+	"echo-lot.app/server/internal/runs"
+	"echo-lot.app/server/internal/store"
+)
+
+// Two accounts, one device each, plus an unlinked device nobody owns.
+func fixture(t *testing.T) (*Server, string, string, string) {
+	t.Helper()
+	dir := t.TempDir()
+	st, err := store.Open(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	rs, err := runs.Open(dir, runs.DefaultPolicy())
+	if err != nil {
+		t.Fatal(err)
+	}
+	enroll := func(name string) string {
+		tok, err := st.NewEnrollToken(time.Hour, "test")
+		if err != nil {
+			t.Fatal(err)
+		}
+		d, err := st.Redeem(tok, name)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return d.ID
+	}
+	mine, theirs, orphan := enroll("mine"), enroll("theirs"), enroll("orphan")
+	if err := st.LinkAccount(mine, "oidc#me", "Me"); err != nil {
+		t.Fatal(err)
+	}
+	if err := st.LinkAccount(theirs, "oidc#you", "You"); err != nil {
+		t.Fatal(err)
+	}
+	for _, d := range []string{mine, theirs, orphan} {
+		if _, err := rs.Put(d, []byte(`{"run":{"id":"r"}}`), true); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return &Server{Store: st, Runs: rs}, mine, theirs, orphan
+}
+
+func user() *adminauth.Session  { return &adminauth.Session{Subject: "oidc#me", Display: "Me"} }
+func admin() *adminauth.Session { return &adminauth.Session{Subject: "local:a", Admin: true} }
+
+func TestVisibleDevicesScopesToAccount(t *testing.T) {
+	s, mine, theirs, orphan := fixture(t)
+
+	got := s.visibleDevices(user())
+	if len(got) != 1 || got[0].ID != mine {
+		t.Fatalf("a user should see only their own device, got %+v", got)
+	}
+
+	all := s.visibleDevices(admin())
+	if len(all) != 3 {
+		t.Fatalf("an admin should see every device, got %d", len(all))
+	}
+	_ = theirs
+	_ = orphan
+}
+
+func TestUnlinkedDevicesBelongToNobody(t *testing.T) {
+	// An enrolled but never-signed-in device is not "everyone's" — a user must not inherit it
+	// just because no account claimed it.
+	s, _, _, orphan := fixture(t)
+	if s.mayTouchRun(user(), orphan) {
+		t.Fatal("an unlinked device was treated as the user's own")
+	}
+}
+
+func TestRunAccessFollowsDeviceOwnership(t *testing.T) {
+	s, mine, theirs, _ := fixture(t)
+
+	if !s.mayTouchRun(user(), mine) {
+		t.Fatal("a user cannot reach their own run")
+	}
+	if s.mayTouchRun(user(), theirs) {
+		t.Fatal("a user reached someone else's run")
+	}
+	if !s.mayTouchRun(admin(), theirs) {
+		t.Fatal("an admin should reach any run")
+	}
+}
+
+func TestAccessEndsWhenTheLinkDoes(t *testing.T) {
+	// Ownership is read from the device list on every request rather than captured at sign-in,
+	// so unlinking takes effect immediately — a session issued while linked must not keep working.
+	s, mine, _, _ := fixture(t)
+	sess := user()
+	if !s.mayTouchRun(sess, mine) {
+		t.Fatal("precondition: the device should start out owned")
+	}
+	if err := s.Store.LinkAccount(mine, "", ""); err != nil {
+		t.Fatal(err)
+	}
+	if s.mayTouchRun(sess, mine) {
+		t.Fatal("access survived the account link being removed")
+	}
+}
+
+func TestEmptySubjectMatchesNothing(t *testing.T) {
+	// The dangerous degenerate case: a session with no subject must own nothing, not everything
+	// that happens to have an empty account id.
+	s, _, _, _ := fixture(t)
+	anon := &adminauth.Session{Subject: "", Display: ""}
+	if got := s.visibleDevices(anon); len(got) != 0 {
+		t.Fatalf("an empty subject matched %d devices", len(got))
+	}
+}

server/internal/canarydns/canarydns.go

@@ -63,20 +63,24 @@ type Server struct {
 	nsName    string // this server's own name for NS/authority answers
 	primaryV4 netip.Addr
 	primaryV6 netip.Addr
+	retention time.Duration // query-log age limit; <= 0 means only the ring cap bounds it
 
 	mu  sync.Mutex
 	log []Query // ring, newest last
-	retainTo time.Time
 }
 
 const logCap = 8192
 
 // New creates a server for zone (with or without trailing dot). nsName is the
 // server's own hostname (for the zone's NS record); primary v4/v6 are this
-// host's addresses used to answer the zone apex / NS glue.
-func New(zone, nsName string, v4, v6 netip.Addr) *Server {
+// host's addresses used to answer the zone apex / NS glue. retention is how
+// long logged queries are kept (spec §6; the privacy default is 24 h).
+func New(zone, nsName string, v4, v6 netip.Addr, retention time.Duration) *Server {
 	z := strings.ToLower(strings.TrimSuffix(zone, ".")) + "."
-	return &Server{zone: z, nsName: strings.TrimSuffix(nsName, ".") + ".", primaryV4: v4, primaryV6: v6}
+	return &Server{
+		zone: z, nsName: strings.TrimSuffix(nsName, ".") + ".",
+		primaryV4: v4, primaryV6: v6, retention: retention,
+	}
 }
 
 // RecentForPrefix returns logged queries whose qname contains ".<prefix>."
@@ -84,6 +88,7 @@ func New(zone, nsName string, v4, v6 netip.Addr) *Server {
 func (s *Server) RecentForPrefix(prefix string) []Query {
 	s.mu.Lock()
 	defer s.mu.Unlock()
+	s.dropExpiredLocked(time.Now().UTC())
 	needle := "." + strings.ToLower(prefix) + "."
 	var out []Query
 	for _, q := range s.log {
@@ -97,12 +102,34 @@ func (s *Server) RecentForPrefix(prefix string) []Query {
 func (s *Server) record(q Query) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
+	s.dropExpiredLocked(q.At)
 	if len(s.log) >= logCap {
 		s.log = s.log[1:]
 	}
 	s.log = append(s.log, q)
 }
 
+// dropExpiredLocked enforces the retention window on the query log.
+//
+// The 24-hour retention was advertised as the privacy default (spec §6/§7) and then not
+// enforced: the ring only bounded *count*, so on a quiet server a resolver's queries could sit
+// in memory for weeks. Aged out on every write and every read — whichever comes first — so an
+// idle log still forgets on schedule the moment anyone looks. Entries are appended in time
+// order, so expiry is always a prefix of the slice.
+func (s *Server) dropExpiredLocked(now time.Time) {
+	if s.retention <= 0 {
+		return
+	}
+	cutoff := now.Add(-s.retention)
+	i := 0
+	for i < len(s.log) && s.log[i].At.Before(cutoff) {
+		i++
+	}
+	if i > 0 {
+		s.log = append([]Query(nil), s.log[i:]...) // reallocate so the old backing array frees
+	}
+}
+
 // ServeUDP / ServeTCP run read loops; call one per bound address.
 func (s *Server) ServeUDP(conn *net.UDPConn) error {
 	buf := make([]byte, 1500)

server/internal/canarydns/canarydns_test.go

@@ -8,6 +8,7 @@ import (
 	"net"
 	"net/netip"
 	"testing"
+	"time"
 )
 
 // buildQuery makes a single-question DNS query, optionally with an EDNS OPT.
@@ -65,7 +66,7 @@ func parseResponse(t *testing.T, resp []byte) (flags uint16, answers []ans) {
 }
 
 func newTestServer() *Server {
-	return New("c.echo-lot.app", "fmr", netip.MustParseAddr("192.0.2.1"), netip.MustParseAddr("2001:db8::1"))
+	return New("c.echo-lot.app", "fmr", netip.MustParseAddr("192.0.2.1"), netip.MustParseAddr("2001:db8::1"), 24*time.Hour)
 }
 
 func TestReferenceRecords(t *testing.T) {
@@ -159,3 +160,29 @@ func TestOutOfZoneNXDomain(t *testing.T) {
 		t.Fatalf("out-of-zone should be NXDOMAIN, flags=%#x", flags)
 	}
 }
+
+func TestQueryLogRetentionForgetsOldEntries(t *testing.T) {
+	s := newTestServer() // 24 h retention
+	now := time.Now().UTC()
+	s.record(Query{QName: "old.sess1.c.echo-lot.app", At: now.Add(-25 * time.Hour)})
+	s.record(Query{QName: "fresh.sess1.c.echo-lot.app", At: now})
+
+	got := s.RecentForPrefix("sess1")
+	if len(got) != 1 || got[0].QName != "fresh.sess1.c.echo-lot.app" {
+		t.Fatalf("retention not enforced: %+v", got)
+	}
+
+	// Reads must age the log too: an idle server still has to forget on schedule.
+	s.log[0].At = now.Add(-25 * time.Hour)
+	if got := s.RecentForPrefix("sess1"); len(got) != 0 {
+		t.Fatalf("read path did not expire entries: %+v", got)
+	}
+}
+
+func TestZeroRetentionKeepsEverything(t *testing.T) {
+	s := New("c.echo-lot.app", "fmr", netip.MustParseAddr("192.0.2.1"), netip.MustParseAddr("2001:db8::1"), 0)
+	s.record(Query{QName: "ancient.sess1.c.echo-lot.app", At: time.Now().UTC().Add(-1000 * time.Hour)})
+	if got := s.RecentForPrefix("sess1"); len(got) != 1 {
+		t.Fatal("retention 0 must mean 'ring cap only', not 'keep nothing'")
+	}
+}

server/internal/config/addrs_test.go

@@ -0,0 +1,56 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package config
+
+import "testing"
+
+// The fixture is fmr's real UDP listen spec, because the point of deriving these from the bound
+// listeners is that they cannot disagree with what the server actually answers on.
+const fmrUDP = "89.185.109.150:8442,89.185.109.151:8442," +
+	"[2001:1ad0:c4fe:6767::150]:8442,[2001:1ad0:c4fe:6767::151]:8442"
+
+func TestMeasurementAddrsSplitsPrimaryFromReserved(t *testing.T) {
+	c := &Config{
+		UDPListen:     fmrUDP,
+		ReservedAddrs: "89.185.109.151,2001:1ad0:c4fe:6767::151",
+	}
+	ip4, ip6, ip4Alt, ip6Alt := c.MeasurementAddrs()
+	for _, tc := range []struct{ got, want, name string }{
+		{ip4, "89.185.109.150", "ip4"},
+		{ip6, "2001:1ad0:c4fe:6767::150", "ip6"},
+		{ip4Alt, "89.185.109.151", "ip4_alt"},
+		{ip6Alt, "2001:1ad0:c4fe:6767::151", "ip6_alt"},
+	} {
+		if tc.got != tc.want {
+			t.Errorf("%s = %q, want %q", tc.name, tc.got, tc.want)
+		}
+	}
+}
+
+func TestMeasurementAddrsWithNothingReserved(t *testing.T) {
+	// No reservation means no alternate: reporting a second address as the RFC 5780 alternate
+	// when it was never set aside for that would tell a client to expect a redirect that the
+	// server has no intention of sending.
+	c := &Config{UDPListen: fmrUDP}
+	ip4, ip6, ip4Alt, ip6Alt := c.MeasurementAddrs()
+	if ip4 == "" || ip6 == "" {
+		t.Fatalf("primaries should still be found: ip4=%q ip6=%q", ip4, ip6)
+	}
+	if ip4Alt != "" || ip6Alt != "" {
+		t.Errorf("no address is reserved, so there is no alternate; got %q / %q", ip4Alt, ip6Alt)
+	}
+}
+
+func TestMeasurementAddrsIgnoresWhatItCannotRead(t *testing.T) {
+	// A wildcard bind names no address, and a hostname is not resolved here. Either would be a
+	// guess presented to clients as fact.
+	c := &Config{UDPListen: ":8442,probe.example.net:8442,89.185.109.150:8442"}
+	ip4, ip6, _, _ := c.MeasurementAddrs()
+	if ip4 != "89.185.109.150" {
+		t.Errorf("ip4 = %q, want the one address that was actually spelled out", ip4)
+	}
+	if ip6 != "" {
+		t.Errorf("ip6 = %q, want empty — none was configured", ip6)
+	}
+}

server/internal/config/config.go

@@ -41,6 +41,24 @@ type Config struct {
 	// Admin UI / health listener (spec §7: localhost-only by default)
 	AdminListen string // ECHOLOT_ADMIN_LISTEN / --admin-listen
 
+	// ReservedAddrs are IPs reserved for measurement: addresses whose listening state must stay
+	// known, so that "nothing answered on port 443" is a fact about the network rather than a
+	// fact about this server's configuration. Enforced by CheckReserved.
+	ReservedAddrs string // ECHOLOT_RESERVED_ADDRS / --reserved-addrs
+
+	// ControlHostname lets the control plane share port 443 with the admin UI.
+	//
+	// They cannot share a certificate: the control plane is trusted by SPKI pin and so uses a
+	// long-lived self-signed certificate, while a browser needs one a CA vouches for. One name on
+	// one port means one certificate, so sharing the port requires two names — this one selects
+	// the pinned certificate and the control-plane routes by SNI, everything else gets the admin
+	// UI. Empty leaves the control plane on its own listener only.
+	//
+	// Why bother: captive portals and corporate firewalls routinely permit only 80 and 443, which
+	// are exactly the networks this tool exists to diagnose. A control plane on 8443 is
+	// unreachable precisely when it matters most.
+	ControlHostname string // ECHOLOT_CONTROL_HOSTNAME / --control-hostname
+
 	// State directory: device store, generated TLS material.
 	StateDir string // ECHOLOT_STATE_DIR / --state-dir
 
@@ -52,6 +70,11 @@ type Config struct {
 	// e.g. https://git.example.net/api/v1/repos/owner/repo
 	SelfUpdateAPI string // ECHOLOT_SELF_UPDATE_API / --self-update-api
 
+	// SelfUpdatePubKey overrides the release-signing public key baked into the binary
+	// (selfupdate.DefaultPublicKeyB64) — for operators running their own release pipeline
+	// against their own Gitea. Empty = the built-in project key.
+	SelfUpdatePubKey string // ECHOLOT_SELF_UPDATE_PUBKEY / --self-update-pubkey
+
 	// Uploaded-run storage. The default is "anonymous": any enrolled device may upload,
 	// which is what a self-hosted server wants. Operators of shared servers turn it down.
 	UploadsMode         string // ECHOLOT_UPLOADS / --uploads (off|anonymous|account)
@@ -60,6 +83,23 @@ type Config struct {
 	UploadMaxRuns       int    // ECHOLOT_UPLOAD_MAX_RUNS / --upload-max-runs (per device)
 	UploadMinAnon       string // ECHOLOT_UPLOAD_MIN_ANONYMIZATION / --upload-min-anonymization
 
+	// Rate limits (spec §2.5), each applied per credential and per source IP. 0 disables a
+	// ceiling. The UDP ceilings are deliberately above the largest legitimate run (a 200 Mbps
+	// upstream throughput test is ~21k pps of 1472-byte packets), so they only ever catch abuse
+	// — a rate limit that clips a real measurement produces a confidently wrong number.
+	RateSessionsPerMin int // ECHOLOT_RATE_SESSIONS_PER_MIN / --rate-sessions-per-min
+	RateActionsPerMin  int // ECHOLOT_RATE_ACTIONS_PER_MIN / --rate-actions-per-min
+	RateUDPPps         int // ECHOLOT_RATE_UDP_PPS / --rate-udp-pps
+	RateUDPKbps        int // ECHOLOT_RATE_UDP_KBPS / --rate-udp-kbps
+
+	// How long canary DNS query logs are kept, in hours (spec §6; privacy default 24).
+	DNSLogRetentionH int // ECHOLOT_DNS_LOG_RETENTION_H / --dns-log-retention-h
+
+	// How long relayed adb endpoints are kept, in hours. Same 24-hour default and the same
+	// reasoning as the DNS log: the value is a LAN address, it stops being true within minutes,
+	// and there is nothing to gain from remembering it afterwards.
+	ADBEndpointRetentionH int // ECHOLOT_ADB_ENDPOINT_RETENTION_H / --adb-endpoint-retention-h
+
 	// Client compatibility window. Bounds are SemVer; an empty maximum means unbounded. The
 	// defaults sit at breaking boundaries, so shipping a patch never requires changing them.
 	MinAppVersion string // ECHOLOT_MIN_APP_VERSION / --min-app-version
@@ -162,9 +202,12 @@ func Load(args []string) (*Config, *Actions, error) {
 	fs.StringVar(&c.HTTPEchoListen, "http-echo-listen", envOr("HTTP_ECHO_LISTEN", ""), "optional CLEARTEXT http-echo listen address(es); empty disables (spec §4)")
 	fs.StringVar(&c.MTUProbeTargets, "mtu-probe-targets", envOr("MTU_PROBE_TARGETS", "1.1.1.1,2606:4700:4700::1111"), "egress-MTU self-proof anchors, comma-separated")
 	fs.StringVar(&c.AdminListen, "admin-listen", envOr("ADMIN_LISTEN", "127.0.0.1:8444"), "admin/health listen address (keep localhost)")
+	fs.StringVar(&c.ControlHostname, "control-hostname", envOr("CONTROL_HOSTNAME", ""), "hostname that selects the pinned control-plane certificate when sharing the admin UI's port")
+	fs.StringVar(&c.ReservedAddrs, "reserved-addrs", envOr("RESERVED_ADDRS", ""), "comma-separated IPs reserved for measurement; no listener but the STUN alternate may bind them")
 	fs.StringVar(&c.StateDir, "state-dir", envOr("STATE_DIR", defaultStateDir()), "state directory (device store, generated TLS)")
 	fs.StringVar(&c.Name, "name", envOr("NAME", "echolot"), "server profile name")
 	fs.StringVar(&c.SelfUpdateAPI, "self-update-api", envOr("SELF_UPDATE_API", ""), "Gitea repo API base for self-update; empty disables")
+	fs.StringVar(&c.SelfUpdatePubKey, "self-update-pubkey", envOr("SELF_UPDATE_PUBKEY", ""), "release-signing public key (base64 ed25519) self-update verifies against; empty uses the built-in project key")
 	fs.StringVar(&c.UploadsMode, "uploads", envOr("UPLOADS", "anonymous"), "who may upload measurement runs: off|anonymous|account")
 	fs.Int64Var(&c.UploadMaxBytes, "upload-max-bytes", int64(envInt("UPLOAD_MAX_BYTES", 4<<20)), "largest accepted uploaded run, bytes")
 	fs.IntVar(&c.UploadRetentionDays, "upload-retention-days", envInt("UPLOAD_RETENTION_DAYS", 90), "delete uploaded runs older than this; 0 disables")
@@ -183,6 +226,12 @@ func Load(args []string) (*Config, *Actions, error) {
 	fs.StringVar(&c.ACMEHTTPListen, "acme-http-listen", envOr("ACME_HTTP_LISTEN", ""), "port-80 listener for ACME HTTP-01 challenges and http->https redirects")
 	fs.StringVar(&c.ACMEWebroot, "acme-webroot", envOr("ACME_WEBROOT", ""), "directory an ACME client writes challenges into (default <state-dir>/acme)")
 	fs.StringVar(&c.PublicControlURL, "public-url", envOr("PUBLIC_URL", ""), "public control-plane URL for enrollment links, e.g. https://probe.example.net:8443")
+	fs.IntVar(&c.RateSessionsPerMin, "rate-sessions-per-min", envInt("RATE_SESSIONS_PER_MIN", 10), "per-credential and per-IP ceiling on session creation (spec §2.5); 0 disables")
+	fs.IntVar(&c.RateActionsPerMin, "rate-actions-per-min", envInt("RATE_ACTIONS_PER_MIN", 60), "per-credential and per-IP ceiling on §5 actions; 0 disables")
+	fs.IntVar(&c.RateUDPPps, "rate-udp-pps", envInt("RATE_UDP_PPS", 25_000), "per-credential and per-IP data-plane packet ceiling, packets/s, silent drop; 0 disables")
+	fs.IntVar(&c.RateUDPKbps, "rate-udp-kbps", envInt("RATE_UDP_KBPS", 250_000), "per-credential and per-IP data-plane byte ceiling, kbit/s, silent drop; 0 disables")
+	fs.IntVar(&c.DNSLogRetentionH, "dns-log-retention-h", envInt("DNS_LOG_RETENTION_H", 24), "hours canary DNS query logs are kept (spec §6 privacy default 24); 0 keeps until the ring overwrites")
+	fs.IntVar(&c.ADBEndpointRetentionH, "adb-endpoint-retention-h", envInt("ADB_ENDPOINT_RETENTION_H", 24), "hours a relayed adb endpoint is kept (dev tooling; see server/README.md); 0 keeps it until the device replaces it")
 	fs.StringVar(&c.MinAppVersion, "min-app-version", envOr("MIN_APP_VERSION", "0.2.0"), "oldest app version this server will serve (SemVer, inclusive)")
 	fs.StringVar(&c.MaxAppVersion, "max-app-version", envOr("MAX_APP_VERSION", "1.0.0"), "first app version this server will refuse (SemVer, exclusive); empty = unbounded")
 	fs.BoolVar(&c.Docker, "docker", envOr("DOCKER", "") == "1", "force container mode (config from env, no systemd/self-update)")
@@ -195,6 +244,7 @@ func Load(args []string) (*Config, *Actions, error) {
 	fs.BoolVar(&a.SetAdminPassword, "set-admin-password", false,
 		"set the break-glass admin password (username as --admin-user, password read from stdin) and exit")
 	fs.StringVar(&c.AdminUser, "admin-user", envOr("ADMIN_USER", "admin"), "username for the break-glass admin")
+	fs.StringVar(&a.MintEnrollToken, "mint-enroll-token", "", "mint a single-use enrollment link (argument is a note for the audit log) and exit")
 	fs.BoolVar(&a.SelfUpdate, "self-update", false, "check for a newer release, replace this binary, and exit")
 	fs.BoolVar(&a.Version, "version", false, "print version and exit")
 
@@ -209,13 +259,16 @@ func Load(args []string) (*Config, *Actions, error) {
 	// is a usage error rather than success — otherwise a service manager sees a clean exit and
 	// concludes the server ran and finished.
 	if !a.Serve && !a.InstallSystemd && !a.UninstallSystemd && !a.SelfUpdate &&
-		!a.SetAdminPassword && !a.Version {
+		!a.SetAdminPassword && !a.Version && a.MintEnrollToken == "" {
 		a.Help = true
 	}
 	if a.Serve {
 		if err := c.checkAdminExposure(); err != nil {
 			return nil, nil, err
 		}
+		if err := c.CheckReserved(c.Listeners()); err != nil {
+			return nil, nil, err
+		}
 	}
 	if c.Docker && (a.InstallSystemd || a.UninstallSystemd || a.SelfUpdate) {
 		return nil, nil, fmt.Errorf("systemd/self-update actions are native-mode only (container detected; override with ECHOLOT_DOCKER=0 if this is wrong)")
@@ -276,6 +329,66 @@ func (c *Config) checkAdminExposure() error {
 	return nil
 }
 
+// Listeners enumerates every configured listen spec, for CheckReserved.
+//
+// Kept as one list here rather than checked at each call site, so a listener added later is
+// caught by the compiler when this function is updated — and, more to the point, so that the
+// person adding one sees the reserved-address rule exists at all.
+func (c *Config) Listeners() []Listener {
+	return []Listener{
+		// The instrument: these belong on the reserved addresses as much as anywhere.
+		{Name: "control-listen", Spec: c.ControlListen, Measurement: true},
+		{Name: "udp-listen", Spec: c.UDPListen, Measurement: true},
+		{Name: "tcp-listen", Spec: c.TCPListen, Measurement: true},
+		{Name: "dns-listen", Spec: c.DNSListen, Measurement: true},
+		{Name: "stun-listen", Spec: c.StunListen, Measurement: true},
+		// http-echo is deliberately not marked as measurement: it is cleartext HTTP, so on a
+		// reserved address it would be the very listener that ruins the port-80 test.
+		{Name: "http-echo-listen", Spec: c.HTTPEchoListen},
+		// Services. These have no business on an address kept for measuring.
+		{Name: "admin-listen", Spec: c.AdminListen},
+		{Name: "acme-http-listen", Spec: c.ACMEHTTPListen},
+	}
+}
+
+// MeasurementAddrs picks out the addresses this server can be measured on, by family, splitting
+// primaries from the reserved alternates.
+//
+// Derived from what is actually bound rather than configured separately: a second list of the
+// server's own addresses is a second thing to keep in step, and the copy that drifts is the one
+// clients are told about.
+func (c *Config) MeasurementAddrs() (ip4, ip6, ip4Alt, ip6Alt string) {
+	reserved := map[string]bool{}
+	for _, ip := range c.ReservedIPs() {
+		reserved[ip.String()] = true
+	}
+	// The UDP data plane binds every address a client may be pointed at, which makes it the
+	// honest source for this.
+	for _, a := range Addrs(c.UDPListen) {
+		host, _, err := net.SplitHostPort(a)
+		if err != nil {
+			continue
+		}
+		host = strings.Trim(host, "[]")
+		ip := net.ParseIP(host)
+		if ip == nil {
+			continue
+		}
+		alt := reserved[ip.String()]
+		switch {
+		case ip.To4() != nil && alt && ip4Alt == "":
+			ip4Alt = host
+		case ip.To4() != nil && !alt && ip4 == "":
+			ip4 = host
+		case ip.To4() == nil && alt && ip6Alt == "":
+			ip6Alt = host
+		case ip.To4() == nil && !alt && ip6 == "":
+			ip6 = host
+		}
+	}
+	return
+}
+
 // Addrs splits a comma-separated listen spec into individual addresses.
 // Explicit per-address binds matter on multi-IP hosts: a wildcard bind
 // (":8443") would also claim addresses reserved for other purposes (e.g. an
@@ -303,6 +416,13 @@ type Actions struct {
 	UninstallSystemd bool
 	SelfUpdate       bool
 	SetAdminPassword bool
+	// MintEnrollToken is the note to record against a freshly minted enrollment link.
+	//
+	// A local action rather than an HTTP endpoint: whoever can run this binary against the state
+	// directory already has every privilege the server has, so authenticating them to themselves
+	// would be theatre — and an unauthenticated endpoint on loopback is how the admin API was
+	// briefly reachable from the network by accident.
+	MintEnrollToken string
 	Version          bool
 }
 

server/internal/config/reserved.go

@@ -0,0 +1,123 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package config
+
+import (
+	"fmt"
+	"net"
+	"sort"
+	"strings"
+)
+
+// Listener is one configured listen spec, named for the error message.
+type Listener struct {
+	Name string // the flag/env this came from, e.g. "control-listen"
+	Spec string // comma-separated listen addresses
+	// Measurement marks a listener that is part of the instrument rather than a service on the
+	// host. Those belong on the reserved addresses — STUN's RFC 5780 alternate, the UDP data
+	// plane, the canary DNS — and reserving an address only to forbid the measurements that need
+	// it would defeat the purpose.
+	Measurement bool
+}
+
+// webPorts are the ports whose closed state on a reserved address is itself the measurement.
+//
+// A TLS handshake that completes on a port known not to be listening proves interception, with no
+// competing explanation. That proof is the whole reason for reserving an address, and it survives
+// exactly as long as nothing binds these two ports there.
+var webPorts = map[string]bool{"80": true, "443": true}
+
+// CheckReserved refuses to start when a listener would occupy an address reserved for measurement.
+//
+// The reserved addresses are the instrument, not the service. Their diagnostic value comes from
+// their listening state being *known*: if nothing listens on port 443 there, then a TLS handshake
+// that completes proves something on the path intercepted it, with no other explanation available.
+// One stray listener silently converts that proof into an ambiguity.
+//
+// This is a hard stop rather than a warning for the same reason as [Config.checkAdminExposure]: the
+// failure is invisible. A polluted reserved address does not crash, log, or behave oddly — it just
+// quietly turns a conclusive test into an inconclusive one, and the first symptom is a measurement
+// that says the network is clean when it is not. Nobody reads a warning for that.
+//
+// Wildcard binds are the realistic way this happens. Every listener defaults to ":port", and the
+// next one added will be copied from an existing default; that binds every address on the host,
+// reserved ones included, without anyone deciding to.
+func (c *Config) CheckReserved(listeners []Listener) error {
+	reserved := c.ReservedIPs()
+	if len(reserved) == 0 {
+		return nil
+	}
+	var problems []string
+	for _, l := range listeners {
+		for _, addr := range Addrs(l.Spec) {
+			host, port, err := net.SplitHostPort(addr)
+			if err != nil {
+				// Not host:port — a bare port or something malformed. Leave it to the listener
+				// itself to complain; guessing here would produce a confusing error about the
+				// wrong problem.
+				continue
+			}
+			host = strings.Trim(host, "[]")
+			if host == "" || host == "0.0.0.0" || host == "::" {
+				problems = append(problems, fmt.Sprintf(
+					"  --%s=%q binds every address on this host, including the reserved ones",
+					l.Name, addr))
+				continue
+			}
+			ip := net.ParseIP(host)
+			if ip == nil {
+				continue // a hostname; cannot resolve it here without lying about what we checked
+			}
+			for _, r := range reserved {
+				if !ip.Equal(r) {
+					continue
+				}
+				switch {
+				case webPorts[port]:
+					problems = append(problems, fmt.Sprintf(
+						"  --%s=%q puts port %s on reserved address %s, which is the one thing "+
+							"that address exists to keep closed", l.Name, addr, port, r))
+				case !l.Measurement:
+					problems = append(problems, fmt.Sprintf(
+						"  --%s=%q binds reserved address %s; only measurement listeners belong there",
+						l.Name, addr, r))
+				}
+			}
+		}
+	}
+	if len(problems) == 0 {
+		return nil
+	}
+	sort.Strings(problems)
+	return fmt.Errorf(
+		"refusing to start: these listeners would occupy addresses reserved for measurement\n%s\n"+
+			"\nReserved: %s\n"+
+			"Those addresses are the instrument. A test can only prove interception on a port that\n"+
+			"is known not to be listening, so anything bound there destroys the conclusion rather\n"+
+			"than merely sharing the address.\n"+
+			"  Fix it one of three ways:\n"+
+			"    - bind each listener to explicit service addresses instead of a wildcard\n"+
+			"    - remove the address from ECHOLOT_RESERVED_ADDRS if it is no longer reserved\n"+
+			"    - unset ECHOLOT_RESERVED_ADDRS if this host has no reserved addresses",
+		strings.Join(problems, "\n"), joinIPs(reserved))
+}
+
+// ReservedIPs parses the configured reserved addresses, ignoring anything unparseable.
+func (c *Config) ReservedIPs() []net.IP {
+	var out []net.IP
+	for _, s := range Addrs(c.ReservedAddrs) {
+		if ip := net.ParseIP(strings.Trim(s, "[]")); ip != nil {
+			out = append(out, ip)
+		}
+	}
+	return out
+}
+
+func joinIPs(ips []net.IP) string {
+	s := make([]string, 0, len(ips))
+	for _, ip := range ips {
+		s = append(s, ip.String())
+	}
+	return strings.Join(s, ", ")
+}

server/internal/config/reserved_test.go

@@ -0,0 +1,151 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package config
+
+import (
+	"strings"
+	"testing"
+)
+
+const (
+	svc4 = "89.185.109.150"
+	res4 = "89.185.109.151"
+	res6 = "2001:1ad0:c4fe:6767::151"
+)
+
+func withReserved(l ...Listener) error {
+	c := &Config{ReservedAddrs: res4 + "," + res6}
+	return c.CheckReserved(l)
+}
+
+func TestWildcardBindIsRefused(t *testing.T) {
+	// The realistic failure: every listener defaults to ":port", and the next one added gets
+	// copied from an existing default. Nobody decides to claim the reserved address; it just
+	// happens, and nothing looks wrong afterwards.
+	err := withReserved(Listener{Name: "control-listen", Spec: ":8443"})
+	if err == nil {
+		t.Fatal("a wildcard bind was allowed while addresses were reserved")
+	}
+	if !strings.Contains(err.Error(), "binds every address") {
+		t.Fatalf("the error should say why a wildcard is the problem, got: %v", err)
+	}
+}
+
+func TestWebPortsOnReservedAreRefusedEvenForMeasurement(t *testing.T) {
+	// The strictest rule, and the one carrying the diagnostic value: 80 and 443 must stay closed
+	// on a reserved address whatever wants them, because their closed state *is* the measurement.
+	for _, spec := range []string{res4 + ":443", "[" + res6 + "]:80"} {
+		err := withReserved(Listener{Name: "control-listen", Spec: spec, Measurement: true})
+		if err == nil {
+			t.Fatalf("port 80/443 on a reserved address was allowed: %q", spec)
+		}
+		if !strings.Contains(err.Error(), "keep closed") {
+			t.Errorf("the error should explain what is lost, got: %v", err)
+		}
+	}
+}
+
+func TestServiceOnReservedIsRefused(t *testing.T) {
+	if err := withReserved(Listener{Name: "admin-listen", Spec: res4 + ":8444"}); err == nil {
+		t.Fatal("a service was allowed onto a reserved address")
+	}
+}
+
+func TestMeasurementListenersBelongOnReserved(t *testing.T) {
+	// The live fmr config: the UDP data plane, canary DNS and STUN all bind the reserved pair on
+	// purpose. A guard that refused this would be describing a rule nobody wants.
+	err := withReserved(
+		Listener{Name: "udp-listen", Spec: res4 + ":8442,[" + res6 + "]:8442", Measurement: true},
+		Listener{Name: "dns-listen", Spec: res4 + ":53,[" + res6 + "]:53", Measurement: true},
+		Listener{Name: "stun-listen", Spec: res4 + ":3478", Measurement: true},
+	)
+	if err != nil {
+		t.Fatalf("measurement listeners must be allowed on reserved addresses: %v", err)
+	}
+}
+
+func TestServiceAddressesAreFine(t *testing.T) {
+	err := withReserved(
+		Listener{Name: "control-listen", Spec: svc4 + ":8443,[2001:1ad0:c4fe:6767::150]:8443"},
+		Listener{Name: "admin-listen", Spec: "127.0.0.1:8444"},
+	)
+	if err != nil {
+		t.Fatalf("service addresses should be allowed: %v", err)
+	}
+}
+
+func TestHttpEchoIsNotTreatedAsMeasurement(t *testing.T) {
+	// http-echo is cleartext HTTP. On a reserved address it is precisely the listener that would
+	// ruin the port-80 test, so it does not get the measurement exemption.
+	if err := withReserved(Listener{Name: "http-echo-listen", Spec: res4 + ":8080"}); err == nil {
+		t.Fatal("http-echo was allowed onto a reserved address")
+	}
+}
+
+func TestNoReservationMeansNoOpinion(t *testing.T) {
+	// A host with nothing reserved must keep working exactly as before, wildcards included.
+	c := &Config{}
+	if err := c.CheckReserved([]Listener{{Name: "control-listen", Spec: ":8443"}}); err != nil {
+		t.Fatalf("with no reserved addresses this must not interfere: %v", err)
+	}
+}
+
+func TestEveryOffenderIsNamed(t *testing.T) {
+	// Reporting one problem at a time turns a config fix into several restart cycles, and on a
+	// remote host each cycle is a chance to lock yourself out.
+	err := withReserved(
+		Listener{Name: "control-listen", Spec: ":8443"},
+		Listener{Name: "tcp-listen", Spec: res4 + ":8441"},
+	)
+	if err == nil {
+		t.Fatal("expected a refusal")
+	}
+	for _, want := range []string{"control-listen", "tcp-listen"} {
+		if !strings.Contains(err.Error(), want) {
+			t.Errorf("the error should name %s; got: %v", want, err)
+		}
+	}
+}
+
+func TestHostnamesAreNotGuessedAt(t *testing.T) {
+	// Resolving here would check a name against whatever DNS says at startup, which is not
+	// necessarily what it will say later — and a guard that is sometimes right is worse than one
+	// with a stated limit.
+	if err := withReserved(Listener{Name: "control-listen", Spec: "fmr-1.echo-lot.app:8443"}); err != nil {
+		t.Fatalf("a hostname must be left alone, not resolved: %v", err)
+	}
+}
+
+func TestListenersCoversEverySpec(t *testing.T) {
+	// A listener missing from Listeners() is invisible to the guard, which is the one way this
+	// protection fails silently. Fill every spec with the reserved address: each one that is
+	// actually enumerated produces a complaint naming it.
+	// Every spec on port 443 of the reserved address: the web-port rule applies to measurement
+	// listeners too, so each one that is genuinely enumerated must produce a complaint.
+	c := &Config{
+		ReservedAddrs:  res4,
+		ControlListen:  res4 + ":443",
+		UDPListen:      res4 + ":443",
+		TCPListen:      res4 + ":443",
+		DNSListen:      res4 + ":443",
+		HTTPEchoListen: res4 + ":443",
+		AdminListen:    res4 + ":443",
+		ACMEHTTPListen: res4 + ":443",
+		StunListen:     res4 + ":443",
+	}
+	err := c.CheckReserved(c.Listeners())
+	if err == nil {
+		t.Fatal("expected a refusal")
+	}
+	// Every spec is on the reserved address; the web-port rule catches even the measurement ones,
+	// so anything missing from Listeners() is invisible here and that is what this asserts.
+	for _, want := range []string{
+		"control-listen", "udp-listen", "tcp-listen", "dns-listen",
+		"http-echo-listen", "admin-listen", "acme-http-listen", "stun-listen",
+	} {
+		if !strings.Contains(err.Error(), want) {
+			t.Errorf("%s is not enumerated in Listeners(), so the guard cannot see it", want)
+		}
+	}
+}

server/internal/control/control.go

@@ -16,6 +16,7 @@ import (
 	"encoding/hex"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 	"log/slog"
 	"net"
@@ -29,6 +30,7 @@ import (
 	"echo-lot.app/server/internal/compat"
 	"echo-lot.app/server/internal/dataplane"
 	"echo-lot.app/server/internal/oidc"
+	"echo-lot.app/server/internal/ratelimit"
 	"echo-lot.app/server/internal/runs"
 	"echo-lot.app/server/internal/session"
 	"echo-lot.app/server/internal/store"
@@ -57,7 +59,8 @@ type Server struct {
 	// DelayedEcho schedules/sends a DELAYED_ECHO for a session (may be nil).
 	DelayedEcho func(sess *session.Session, actionID string) error
 	// Granted server->client sends (spec §5). Both consume an asymmetric grant.
-	DownTrain func(sess *session.Session, g *session.Grant, count, sizeBytes, intervalUs int) (int, error)
+	// DownTrain's dscp is -1 for "leave the socket's default marking alone".
+	DownTrain func(sess *session.Session, g *session.Grant, count, sizeBytes, intervalUs, dscp int) (int, error)
 	BigSend   func(sess *session.Session, g *session.Grant, sizes []int, df bool) ([]dataplane.BigSendResult, error)
 	// OIDC verifies ID tokens presented by the *app* (may be nil).
 	OIDC *oidc.Verifier
@@ -80,6 +83,10 @@ type Server struct {
 	CanaryQueries func(sessionPrefix string) any
 	// CanaryZone is surfaced in the profile so the app knows what to query.
 	CanaryZone string
+	// The addresses this server can be measured on. The "_alt" pair is the second address
+	// RFC 5780 behaviour discovery redirects to, and the one reserved from services so that
+	// nothing answering there is itself a measurement.
+	IP4, IP6, IP4Alt, IP6Alt string
 	// ProvenGood reports the server's self-test signal (may be nil). Surfaced
 	// in the profile so a client can trust — or skip — MTU tests: if the
 	// server's own egress isn't full-MTU, client MTU results measure the
@@ -93,6 +100,11 @@ type Server struct {
 	// AppRange is the app-version window this server will serve. Zero value means the built-in
 	// default (see DefaultAppRange).
 	AppRange compat.Range
+
+	// Spec §2.5 token buckets, keyed per credential and per source IP inside the limiter.
+	// Nil disables a ceiling (config value 0).
+	RateSessions *ratelimit.Limiter // POST /v1/sessions
+	RateActions  *ratelimit.Limiter // POST /v1/sessions/{id}/actions
 }
 
 // AppVersionHeader is how a client states its version. A client too old to send it is treated as
@@ -102,7 +114,12 @@ const AppVersionHeader = "X-Echolot-App-Version"
 
 // ProtocolVersion is the wire contract (probe-protocol.md) this build implements. It is what the
 // version window is really about; the release version is only a proxy for it.
-const ProtocolVersion = "1.0.0"
+//
+// 1.0.1: upstream trains (§3.2 types 0x03/0x04/0x05) and the action-id bytes at payload[8:16]
+// of granted packets. Patch, not minor: both are additive — a client that never sends
+// TRAIN_REPORT_REQ and never reads granted payloads (today's client reads only header fields)
+// sees no difference, so the fleet must not be split over it (§8.1).
+const ProtocolVersion = "1.0.1"
 
 // SchemaVersion is the measurement-document format this server can store.
 const SchemaVersion = "1.0.0"
@@ -160,10 +177,12 @@ func (s *Server) Handler() http.Handler {
 
 	gate := s.requireCompatibleApp
 	mux.HandleFunc("POST /v1/enroll", gate(s.enroll))
-	mux.HandleFunc("POST /v1/sessions", gate(s.newSession))
+	// §2.5 buckets sit on the two endpoints that make the server DO things — create state,
+	// send traffic. GET /v1/profile stays ungated on every axis (see above).
+	mux.HandleFunc("POST /v1/sessions", gate(s.rateLimited(s.RateSessions, s.newSession)))
 	mux.HandleFunc("DELETE /v1/sessions/{id}", gate(s.deleteSession))
 	mux.HandleFunc("GET /v1/sessions/{id}/observations", gate(s.observations))
-	mux.HandleFunc("POST /v1/sessions/{id}/actions", gate(s.actions))
+	mux.HandleFunc("POST /v1/sessions/{id}/actions", gate(s.rateLimited(s.RateActions, s.actions)))
 	mux.HandleFunc("POST /v1/echo", gate(s.httpEcho))
 	mux.HandleFunc("GET /v1/tls-reference", gate(s.tlsReference))
 	mux.HandleFunc("POST /v1/runs", gate(s.uploadRun))
@@ -173,7 +192,11 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("POST /v1/account/link", gate(s.linkAccount))
 	mux.HandleFunc("DELETE /v1/account/link", gate(s.unlinkAccount))
 	mux.HandleFunc("GET /v1/account", gate(s.accountStatus))
-	// TODO(spec §5): frag_send, throughput (both build on the same grant machinery)
+	// Dev tooling, not protocol (see devtools.go). It shares the actions bucket rather than
+	// getting a ceiling of its own: it is a POST from an enrolled device that makes the server
+	// write, which is exactly what that limit is for, and a knob nobody tunes is a knob that
+	// eventually disagrees with the one next to it.
+	mux.HandleFunc("POST /v1/devtools/adb-endpoint", gate(s.rateLimited(s.RateActions, s.submitADBEndpoint)))
 	return mux
 }
 
@@ -195,6 +218,37 @@ func selftestSignal(f func() (bool, bool)) map[string]any {
 	return map[string]any{"mtu_ok": mtuOK, "sysctl_ok": sysctlOK}
 }
 
+// rateLimited enforces one §2.5 bucket policy on an endpoint: a token per credential AND one per
+// source IP. Two keys because each closes the other's hole — keyed only by credential, one
+// address cycles through credentials; keyed only by address, one credential rides many
+// addresses. The refusal is 429 with Retry-After, which is the whole point of a token bucket
+// over a hard drop here: a well-behaved client is told when to come back.
+func (s *Server) rateLimited(l *ratelimit.Limiter, next http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		okCred, waitCred := l.Allow("cred:" + bearer(r))
+		okIP, waitIP := l.Allow("ip:" + remoteIP(r))
+		if !okCred || !okIP {
+			wait := max(waitCred, waitIP)
+			secs := int(wait/time.Second) + 1 // Retry-After is whole seconds, rounded up
+			w.Header().Set("Retry-After", strconv.Itoa(secs))
+			writeJSON(w, http.StatusTooManyRequests, map[string]any{
+				"error": "rate limited", "retry_after_s": secs,
+			})
+			return
+		}
+		next(w, r)
+	}
+}
+
+// remoteIP is the request's source address without the port, for rate-limit keys.
+func remoteIP(r *http.Request) string {
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		return r.RemoteAddr
+	}
+	return strings.Trim(host, "[]")
+}
+
 // sessionAuth resolves {id} and requires the bearer to be the owning device.
 func (s *Server) sessionAuth(w http.ResponseWriter, r *http.Request) *session.Session {
 	dev := s.Store.DeviceByCredential(bearer(r))
@@ -231,7 +285,13 @@ func (s *Server) observations(w http.ResponseWriter, r *http.Request) {
 		dnsCanary = s.CanaryQueries(sess.ID[:16]) // the session's wire prefix
 	}
 	writeJSON(w, http.StatusOK, map[string]any{
-		"udp":          map[string]any{"packets_seen": packetsSeen, "packets": udp},
+		"udp": map[string]any{
+			"packets_seen": packetsSeen,
+			"packets":      udp,
+			// The per-train received view (spec §6 "trains"), columnar like the wire report —
+			// the flat packet list above stays for clients that predate trains.
+			"trains": trainsJSON(sess.Trains()),
+		},
 		"tcp": tcp,
 		"connect_back": cb,
 		// The sender's own count, which is what makes the receiver's count mean something.
@@ -260,6 +320,7 @@ func (s *Server) actions(w http.ResponseWriter, r *http.Request) {
 		SizeBytes  int    `json:"size_bytes"`
 		IntervalUs int    `json:"interval_us"`
 		SizesBytes []int  `json:"sizes_bytes"`
+		DSCP       *int   `json:"dscp"`
 		DF         *bool  `json:"df"`
 		Mode       string `json:"mode"`
 		FragBytes  int    `json:"frag_bytes"`
@@ -322,6 +383,11 @@ func (s *Server) actions(w http.ResponseWriter, r *http.Request) {
 			writeJSON(w, http.StatusNotImplemented, map[string]string{"error": "downtrain not wired"})
 			return
 		}
+		dscp, err := dscpArg(req.DSCP)
+		if err != nil {
+			writeJSON(w, http.StatusBadRequest, map[string]string{"error": err.Error()})
+			return
+		}
 		// A downstream train sends far more than it receives, so it needs a grant (§3.4).
 		count := clamp(req.Count, 1, 5000)
 		size := clamp(req.SizeBytes, dataMinPacket, 1500)
@@ -332,13 +398,20 @@ func (s *Server) actions(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 		go func() {
-			sent, err := s.DownTrain(sess, g, count, size, interval)
+			sent, err := s.DownTrain(sess, g, count, size, interval, dscp)
 			slog.Info("downtrain finished", "action", actionID, "sent", sent, "bytes", g.Sent(), "err", err)
 		}()
-		writeJSON(w, http.StatusAccepted, map[string]any{
+		resp := map[string]any{
 			"action_id": actionID, "count": count, "size_bytes": size, "interval_us": interval,
 			"grant": map[string]any{"max_bytes": g.MaxBytes, "max_kbps": g.MaxKbps},
-		})
+		}
+		if dscp >= 0 {
+			resp["dscp"] = dscp
+			// Told up front, not discovered: a client measuring DSCP survival on a burst the
+			// server could not mark would conclude the network stripped it.
+			resp["dscp_applied"] = dataplane.TOSSupported
+		}
+		writeJSON(w, http.StatusAccepted, resp)
 
 	case "big_send":
 		if s.BigSend == nil {
@@ -521,8 +594,54 @@ func (s *Server) maxDFPayload(sess *session.Session) int {
 	return mtu - overhead
 }
 
-// dataMinPacket is the smallest datagram that still carries a header + a little payload.
-const dataMinPacket = 40
+// dscpArg validates the optional downtrain dscp parameter (spec §5). Absent means -1: leave the
+// socket's default marking alone, which is different from asking for DSCP 0 (explicitly
+// best-effort). Out-of-range values are refused rather than clamped — a clamped 46→63 would mark
+// the burst with a class the client never asked for and silently change what the test measures.
+func dscpArg(v *int) (int, error) {
+	if v == nil {
+		return -1, nil
+	}
+	if *v < 0 || *v > 63 {
+		return 0, fmt.Errorf("dscp %d is out of range: the field is 6 bits (0..63)", *v)
+	}
+	return *v, nil
+}
+
+// trainsJSON renders the per-train received view columnar — one array per field, matching the
+// wire report and the schema's train-evidence shape — with []int for the byte-wide columns
+// because encoding/json would base64 a []uint8.
+func trainsJSON(trains []session.Train) []map[string]any {
+	out := make([]map[string]any, 0, len(trains))
+	for _, t := range trains {
+		n := len(t.Entries)
+		seq := make([]uint32, n)
+		trx := make([]int64, n)
+		size := make([]int, n)
+		ttl := make([]int, n)
+		dscp := make([]int, n)
+		ecn := make([]int, n)
+		for i, e := range t.Entries {
+			seq[i], trx[i], size[i] = e.Seq, e.TRxNs, int(e.Size)
+			ttl[i], dscp[i], ecn[i] = int(e.TTL), int(e.DSCP), int(e.ECN)
+		}
+		out = append(out, map[string]any{
+			"train_id": t.ID,
+			// The loss denominator: every packet counted, whether or not its row was kept.
+			"packets_received": t.Received,
+			"truncated":        t.Truncated,
+			"seq":              seq, "t_rx_ns": trx, "size": size,
+			"ttl": ttl, "dscp": dscp, "ecn": ecn,
+		})
+	}
+	return out
+}
+
+// dataMinPacket is the smallest granted datagram: header + 16 payload bytes, because [8:16] of
+// every granted payload carries the action id. It must match what the senders raise short sizes
+// to, or a minimum-size train's grant is budgeted for fewer bytes than actually leave and the
+// train is cut short by its own arithmetic.
+const dataMinPacket = dataplane.HeaderSize + 16
 
 var noDataPlaneYet = map[string]string{
 	"error": "no data-plane traffic seen yet — send an ECHO first so the destination is verified",
@@ -614,13 +733,7 @@ func (s *Server) profile(w http.ResponseWriter, r *http.Request) {
 		// modified builds and gives clients provenance for the measurement.
 		"source_url":   "", // TODO: stamp from build metadata
 		"capabilities": s.Capabilities,
-		"targets": []map[string]any{{
-			"id":        s.Name,
-			"ip4":       host, // TODO: explicit configured addresses, v6, second STUN addr
-			"udp_port":  s.UDPPort,
-			"tcp_port":  s.TCPPort,
-			"stun_port": s.StunPort,
-		}},
+		"targets": []map[string]any{s.target(host)},
 		"pins":            []string{"pin-sha256:" + s.PinB64},
 		"next_pins":       []string{},
 		"canary_zone":     s.CanaryZone,
@@ -825,13 +938,47 @@ func maxOrEmpty(r compat.Range) string {
 // three parts at once — its own URL, its own SPKI pin, and the token. An operator copying a pin
 // by hand is the step that goes wrong, and a pin wrong by one character does not fail loudly.
 func (s *Server) EnrollmentLink(token string) string {
-	u := s.PublicControlURL
+	return EnrollmentURI(s.PublicControlURL, s.PinB64, token)
+}
+
+// EnrollmentURI is the same assembly without a running server, for the mint-a-link CLI action.
+// Shared rather than reimplemented: two copies of this encoding would eventually disagree, and
+// the failure mode is a pin that looks right and produces an inscrutable TLS error.
+func EnrollmentURI(publicURL, pinB64, token string) string {
 	return "echolot://enroll?v=1" +
-		"&u=" + url.QueryEscape(strings.TrimRight(u, "/")) +
-		"&p=" + url.QueryEscape("pin-sha256:"+s.PinB64) +
+		"&u=" + url.QueryEscape(strings.TrimRight(publicURL, "/")) +
+		"&p=" + url.QueryEscape("pin-sha256:"+pinB64) +
 		"&t=" + url.QueryEscape(token)
 }
 
+// target describes where this server can be measured, so a client can say which address a result
+// came from instead of "the server".
+//
+// The alternates matter as much as the primaries: RFC 5780 behaviour discovery needs a second
+// address to redirect to, and an operator reading a report needs to know which of their addresses
+// a finding refers to. [fallback] is used only when nothing was configured explicitly, so a server
+// that has not been told its own addresses still answers with something usable.
+func (s *Server) target(fallback string) map[string]any {
+	t := map[string]any{
+		"id":        s.Name,
+		"udp_port":  s.UDPPort,
+		"tcp_port":  s.TCPPort,
+		"stun_port": s.StunPort,
+	}
+	ip4 := s.IP4
+	if ip4 == "" {
+		ip4 = fallback
+	}
+	for k, v := range map[string]string{
+		"ip4": ip4, "ip6": s.IP6, "ip4_alt": s.IP4Alt, "ip6_alt": s.IP6Alt,
+	} {
+		if v != "" {
+			t[k] = v
+		}
+	}
+	return t
+}
+
 // upstreamJSON renders the upstream tally with the derived figures already computed, so every
 // consumer does not have to repeat (and risk fumbling) the same arithmetic.
 func upstreamJSON(sess *session.Session) map[string]any {

server/internal/control/devtools.go

@@ -0,0 +1,127 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package control
+
+import (
+	"encoding/json"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/netip"
+	"strings"
+	"time"
+
+	"echo-lot.app/server/internal/store"
+)
+
+// The dev relay: an Echolot instance on a test LAN reports where adbd's wireless-debug listener
+// can be reached, and a developer on another subnet reads it back from the admin UI. Documented in
+// server/README.md; deliberately absent from probe-protocol.md and from the advertised capability
+// list, because it measures nothing — it is scaffolding for driving a test device.
+//
+// It sits on the control plane rather than on a listener of its own, and that is the whole point.
+// The receiver this replaces was a separate service wildcard-bound to 0.0.0.0:443, which silently
+// occupied port 443 on the addresses reserved for measurement and voided the IPv4 interception
+// proof for as long as it ran — and it accepted a port report from anyone who could reach it. Here
+// there is no new port, no wildcard bind, and the device credential authenticates the submitter.
+
+// maxADBNoteLen and maxADBNameLen bound what a submitter can store. Free text from a device ends
+// up in the state file and on an operator's page; a label is a few words, so a few words is what
+// is kept.
+const (
+	maxADBNameLen = 64
+	maxADBNoteLen = 200
+)
+
+// submitADBEndpoint records the calling device's wireless-debug endpoint (POST
+// /v1/devtools/adb-endpoint). Newest report per device wins; see store.PutADBEndpoint.
+func (s *Server) submitADBEndpoint(w http.ResponseWriter, r *http.Request) {
+	dev := s.Store.DeviceByCredential(bearer(r))
+	if dev == nil {
+		writeJSON(w, http.StatusUnauthorized, map[string]string{"error": "unknown credential"})
+		return
+	}
+	var body struct {
+		Host       string `json:"host"`
+		Port       int    `json:"port"`
+		DeviceName string `json:"device_name"`
+		Note       string `json:"note"`
+	}
+	// A few hundred bytes of JSON at most; the limit is here so a stuck or hostile client cannot
+	// stream a body at a handler that has no reason to read one.
+	if err := json.NewDecoder(io.LimitReader(r.Body, 8<<10)).Decode(&body); err != nil {
+		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "bad body"})
+		return
+	}
+	host := strings.TrimSpace(body.Host)
+	if !plausibleHost(host) {
+		writeJSON(w, http.StatusBadRequest, map[string]string{
+			"error": "host must be an IP address or a hostname",
+		})
+		return
+	}
+	if body.Port < 1 || body.Port > 65535 {
+		writeJSON(w, http.StatusBadRequest, map[string]string{
+			"error": "port must be between 1 and 65535",
+		})
+		return
+	}
+	e := store.ADBEndpoint{
+		Device:     dev.ID,
+		Host:       host,
+		Port:       body.Port,
+		DeviceName: clip(body.DeviceName, maxADBNameLen),
+		Note:       clip(body.Note, maxADBNoteLen),
+		ReportedAt: time.Now().UTC(),
+		SourceIP:   remoteIP(r),
+	}
+	if err := s.Store.PutADBEndpoint(e); err != nil {
+		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": err.Error()})
+		return
+	}
+	slog.Info("adb endpoint reported", "device", dev.ID, "name", e.DeviceName,
+		"host", e.Host, "port", e.Port, "from", e.SourceIP)
+	writeJSON(w, http.StatusCreated, map[string]any{
+		"device": e.Device, "host": e.Host, "port": e.Port,
+		"reported_at": e.ReportedAt.Format(time.RFC3339),
+	})
+}
+
+// plausibleHost accepts an IP literal or a DNS-shaped name.
+//
+// A shape check and nothing more: the address is meaningful only on the reporter's own LAN, so
+// this server can never confirm it is reachable or even real. What it can do is refuse a value
+// that could not be an address at all, which keeps junk out of the state file and out of the
+// command an operator is about to paste into a shell.
+func plausibleHost(h string) bool {
+	if h == "" || len(h) > 253 {
+		return false
+	}
+	if _, err := netip.ParseAddr(strings.Trim(h, "[]")); err == nil {
+		return true
+	}
+	for _, label := range strings.Split(strings.TrimSuffix(h, "."), ".") {
+		if label == "" || len(label) > 63 || label[0] == '-' || label[len(label)-1] == '-' {
+			return false
+		}
+		for i := 0; i < len(label); i++ {
+			c := label[i]
+			switch {
+			case c >= 'a' && c <= 'z', c >= 'A' && c <= 'Z', c >= '0' && c <= '9', c == '-':
+			default:
+				return false
+			}
+		}
+	}
+	return true
+}
+
+// clip trims a caller-supplied label to a bounded length.
+func clip(s string, n int) string {
+	s = strings.TrimSpace(s)
+	if len(s) > n {
+		return s[:n]
+	}
+	return s
+}

server/internal/control/devtools_test.go

@@ -0,0 +1,137 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package control
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"echo-lot.app/server/internal/store"
+)
+
+// devtoolsFixture is a server with one enrolled device, and that device's credential.
+func devtoolsFixture(t *testing.T) (*Server, string) {
+	t.Helper()
+	st, err := store.Open(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	st.SetADBEndpointRetention(24 * time.Hour)
+	tok, err := st.NewEnrollToken(time.Hour, "test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	dev, err := st.Redeem(tok, "tablet")
+	if err != nil {
+		t.Fatal(err)
+	}
+	return &Server{Store: st}, dev.Credential
+}
+
+func postEndpoint(t *testing.T, s *Server, cred, body string) *httptest.ResponseRecorder {
+	t.Helper()
+	req := httptest.NewRequest("POST", "/v1/devtools/adb-endpoint", strings.NewReader(body))
+	if cred != "" {
+		req.Header.Set("Authorization", "Bearer "+cred)
+	}
+	rec := httptest.NewRecorder()
+	s.Handler().ServeHTTP(rec, req)
+	return rec
+}
+
+// The receiver this replaces took a port report from anyone who could reach it. This one does not.
+func TestADBEndpointNeedsADeviceCredential(t *testing.T) {
+	s, _ := devtoolsFixture(t)
+	rec := postEndpoint(t, s, "", `{"host":"10.13.102.128","port":45305}`)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("no credential: code=%d, want 401", rec.Code)
+	}
+	rec = postEndpoint(t, s, "not-a-credential", `{"host":"10.13.102.128","port":45305}`)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("wrong credential: code=%d, want 401", rec.Code)
+	}
+	if got := s.Store.ADBEndpoints(); len(got) != 0 {
+		t.Fatalf("an unauthenticated report was stored: %+v", got)
+	}
+}
+
+func TestADBEndpointRejectsImplausibleHostAndPort(t *testing.T) {
+	s, cred := devtoolsFixture(t)
+	for _, body := range []string{
+		`{"host":"","port":45305}`,
+		`{"host":"10.13.102.128 && rm -rf /","port":45305}`,
+		`{"host":"not a host","port":45305}`,
+		`{"host":"-bad.example","port":45305}`,
+		`{"host":"10.13.102.128","port":0}`,
+		`{"host":"10.13.102.128","port":65536}`,
+		`{"host":"10.13.102.128","port":-1}`,
+		`not json at all`,
+	} {
+		rec := postEndpoint(t, s, cred, body)
+		if rec.Code != http.StatusBadRequest {
+			t.Errorf("%s: code=%d, want 400 (%s)", body, rec.Code, strings.TrimSpace(rec.Body.String()))
+		}
+	}
+	if got := s.Store.ADBEndpoints(); len(got) != 0 {
+		t.Fatalf("a rejected report was stored anyway: %+v", got)
+	}
+}
+
+func TestADBEndpointStoresTheObservedSourceAndTheCallersDeviceID(t *testing.T) {
+	s, cred := devtoolsFixture(t)
+	rec := postEndpoint(t, s, cred,
+		`{"host":"10.13.102.128","port":45305,"device_name":"TB330FU","note":"wireless debugging"}`)
+	if rec.Code != http.StatusCreated {
+		t.Fatalf("code=%d body=%s", rec.Code, rec.Body.String())
+	}
+	got := s.Store.ADBEndpoints()
+	if len(got) != 1 {
+		t.Fatalf("got %d rows, want 1", len(got))
+	}
+	e := got[0]
+	if e.Host != "10.13.102.128" || e.Port != 45305 || e.DeviceName != "TB330FU" {
+		t.Fatalf("report not stored as sent: %+v", e)
+	}
+	// The device id comes from the credential and the source IP from the connection, so neither is
+	// something the body can claim.
+	if e.Device == "" {
+		t.Fatal("the submitting device was not recorded")
+	}
+	if e.SourceIP != "192.0.2.1" { // httptest's RemoteAddr
+		t.Fatalf("source IP = %q, want the observed remote address", e.SourceIP)
+	}
+	if e.ReportedAt.IsZero() {
+		t.Fatal("no server-side timestamp was recorded")
+	}
+}
+
+func TestPlausibleHost(t *testing.T) {
+	for _, tc := range []struct {
+		host string
+		want bool
+	}{
+		{"10.13.102.128", true},
+		{"192.168.1.1", true},
+		{"fe80::1", true},
+		{"[2001:db8::1]", true},
+		{"tablet.lan", true},
+		{"tablet", true},
+		{"a-b.example.net.", true},
+		{"", false},
+		{"not a host", false},
+		{"10.0.0.1:5555", false}, // the port is its own field; a host must not smuggle one
+		{"-lead.example", false},
+		{"trail-.example", false},
+		{"a..b", false},
+		{"http://10.0.0.1", false},
+		{strings.Repeat("x", 254), false},
+	} {
+		if got := plausibleHost(tc.host); got != tc.want {
+			t.Errorf("plausibleHost(%q) = %v, want %v", tc.host, got, tc.want)
+		}
+	}
+}

server/internal/control/dscp_test.go

@@ -0,0 +1,27 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package control
+
+import "testing"
+
+func TestDscpArg(t *testing.T) {
+	ptr := func(v int) *int { return &v }
+	for _, tc := range []struct {
+		in      *int
+		want    int
+		wantErr bool
+	}{
+		{nil, -1, false},     // absent: leave the socket alone
+		{ptr(0), 0, false},   // explicit best-effort is not the same as absent
+		{ptr(46), 46, false}, // EF, the value people actually test with
+		{ptr(63), 63, false},
+		{ptr(64), 0, true}, // one past the 6-bit field
+		{ptr(-1), 0, true},
+	} {
+		got, err := dscpArg(tc.in)
+		if (err != nil) != tc.wantErr || got != tc.want {
+			t.Errorf("dscpArg(%v) = %d, err=%v; want %d, wantErr=%v", tc.in, got, err, tc.want, tc.wantErr)
+		}
+	}
+}

server/internal/dataplane/cmsg_linux.go

@@ -0,0 +1,70 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build linux
+
+package dataplane
+
+import (
+	"encoding/binary"
+	"net"
+	"syscall"
+)
+
+// Per-packet TTL and TOS/traffic-class arrive as control messages, and only if asked for at
+// socket setup. These fill the spec §3.3 observation-block fields that were shipped as the 0xFF
+// sentinel until now — received TTL is path-length evidence, the TOS byte is DSCP/ECN survival.
+
+// enableRecvMeta asks the kernel to attach the cmsgs to every received datagram. Both the v4 and
+// the v6 option sets are attempted on every socket: a dual-stack socket delivers v4-mapped
+// traffic through the v6 fd, and the kernel refuses whichever set does not apply. Errors are
+// dropped on purpose — a socket that cannot deliver metadata still serves probes, and the
+// sentinel already says "not observed" for it.
+func enableRecvMeta(conn *net.UDPConn) {
+	raw, err := conn.SyscallConn()
+	if err != nil {
+		return
+	}
+	_ = raw.Control(func(fd uintptr) {
+		_ = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IP_RECVTTL, 1)
+		_ = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IP_RECVTOS, 1)
+		_ = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IPV6, syscall.IPV6_RECVHOPLIMIT, 1)
+		_ = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IPV6, syscall.IPV6_RECVTCLASS, 1)
+	})
+}
+
+// parseMeta extracts TTL and the TOS byte from one datagram's control messages. Anything absent
+// or unparseable keeps the sentinel — reported as unobserved, never guessed.
+func parseMeta(oob []byte) pktMeta {
+	m := pktMeta{TTL: metaUnavailable, TOS: metaUnavailable}
+	if len(oob) == 0 {
+		return m
+	}
+	cmsgs, err := syscall.ParseSocketControlMessage(oob)
+	if err != nil {
+		return m
+	}
+	for _, c := range cmsgs {
+		switch {
+		case c.Header.Level == syscall.IPPROTO_IP && c.Header.Type == syscall.IP_TTL,
+			c.Header.Level == syscall.IPPROTO_IPV6 && c.Header.Type == syscall.IPV6_HOPLIMIT:
+			m.TTL = cmsgValue(c.Data)
+		case c.Header.Level == syscall.IPPROTO_IP && c.Header.Type == syscall.IP_TOS,
+			c.Header.Level == syscall.IPPROTO_IPV6 && c.Header.Type == syscall.IPV6_TCLASS:
+			m.TOS = cmsgValue(c.Data)
+		}
+	}
+	return m
+}
+
+// cmsgValue reads a cmsg the kernel encodes either as a native-endian int (IP_TTL,
+// IPV6_HOPLIMIT, IPV6_TCLASS) or as a single byte (IP_TOS). Both fit a byte by definition.
+func cmsgValue(data []byte) uint8 {
+	switch {
+	case len(data) >= 4:
+		return uint8(binary.NativeEndian.Uint32(data))
+	case len(data) >= 1:
+		return data[0]
+	}
+	return metaUnavailable
+}

server/internal/dataplane/cmsg_other.go

@@ -0,0 +1,15 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build !linux
+
+package dataplane
+
+import "net"
+
+// Per-packet TTL/TOS needs Linux's IP_RECVTTL-family cmsgs. Elsewhere the observation block and
+// train buffers keep the spec §3.3 sentinel (0xFF = not observed) — absent is honest, a guess
+// is not. Deployment targets are Linux; this build exists so the Windows dev loop compiles.
+func enableRecvMeta(_ *net.UDPConn) {}
+
+func parseMeta(_ []byte) pktMeta { return pktMeta{TTL: metaUnavailable, TOS: metaUnavailable} }

server/internal/dataplane/frag_linux.go

@@ -104,8 +104,8 @@ func (s *Server) FragSend(
 		return res, fmt.Errorf("session has no recorded local address")
 	}
 
-	if sizeBytes < HeaderSize+8 {
-		sizeBytes = HeaderSize + 8
+	if sizeBytes < HeaderSize+32 {
+		sizeBytes = HeaderSize + 32
 	}
 	if sizeBytes > 8000 {
 		sizeBytes = 8000
@@ -117,7 +117,10 @@ func (s *Server) FragSend(
 	// The ELT1 packet, signed exactly as any other, then wrapped in UDP.
 	payload := make([]byte, sizeBytes-HeaderSize)
 	binary.BigEndian.PutUint32(payload[0:4], uint32(sizeBytes))
-	copy(payload[4:], mode)
+	// [8:16]: the action id, as on every granted packet (spec §5 correlation); the mode string
+	// sits past the reserved slot.
+	putActionID(payload, g.ActionID)
+	copy(payload[16:], mode)
 	elt := s.buildPacket(sess, TypeFragData, 0, payload)
 
 	udp := buildUDP(local, target, elt)

server/internal/dataplane/granted.go

@@ -21,7 +21,11 @@ import (
 // client measures downstream loss, reordering and jitter from what arrives — the direction an
 // upstream-only train cannot see. Returns how many packets actually went out (the grant may cut
 // it short, which is itself reportable).
-func (s *Server) DownTrain(sess *session.Session, g *session.Grant, count, sizeBytes, intervalUs int) (int, error) {
+//
+// dscp ≥ 0 marks the burst (spec §5 downtrain `dscp`): downstream DSCP survival is the half the
+// client cannot produce itself. Best-effort off Linux — see withTOS/TOSSupported; the action
+// response has already told the client whether the marking was applied.
+func (s *Server) DownTrain(sess *session.Session, g *session.Grant, count, sizeBytes, intervalUs, dscp int) (int, error) {
 	target := sess.DataSource()
 	if !target.IsValid() {
 		return 0, fmt.Errorf("no observed data-plane source")
@@ -30,11 +34,15 @@ func (s *Server) DownTrain(sess *session.Session, g *session.Grant, count, sizeB
 	if conn == nil {
 		return 0, fmt.Errorf("no data-plane socket matches target family")
 	}
-	if sizeBytes < HeaderSize+8 {
-		sizeBytes = HeaderSize + 8
+	if sizeBytes < HeaderSize+16 {
+		sizeBytes = HeaderSize + 16
 	}
 	payload := make([]byte, sizeBytes-HeaderSize)
+	// Payload [8:16] carries the action id on every granted packet, so arriving traffic can be
+	// attributed to the action that caused it (spec §5/§9: test.params.action_id).
+	putActionID(payload, g.ActionID)
 	sent := 0
+	burst := func() error {
 		for i := 0; i < count; i++ {
 			if !g.Allow(sizeBytes) {
 				break // budget or rate exhausted — stop, do not sleep it off
@@ -49,7 +57,18 @@ func (s *Server) DownTrain(sess *session.Session, g *session.Grant, count, sizeB
 				time.Sleep(time.Duration(intervalUs) * time.Microsecond)
 			}
 		}
-	return sent, nil
+		return nil
+	}
+	if dscp >= 0 && TOSSupported {
+		// Same shared-socket borrow as the DF window: dfMu keeps a concurrent burst from riding
+		// along with — or clearing — this marking.
+		s.dfMu.Lock()
+		defer s.dfMu.Unlock()
+		err := withTOS(conn, dscp, burst) // sent must be read after the burst ran, not before
+		return sent, err
+	}
+	err := burst()
+	return sent, err
 }
 
 // BigSendResult records what happened to one requested size. `Sent` false with an EMSGSIZE-ish
@@ -83,8 +102,8 @@ func (s *Server) BigSend(sess *session.Session, g *session.Grant, sizes []int, d
 	results := make([]BigSendResult, 0, len(sizes))
 	burst := func() error {
 		for i, size := range sizes {
-			if size < HeaderSize+8 {
-				size = HeaderSize + 8
+			if size < HeaderSize+16 {
+				size = HeaderSize + 16
 			}
 			if size > 9000 { // jumbo ceiling; beyond this the kernel will refuse anyway
 				size = 9000
@@ -96,6 +115,8 @@ func (s *Server) BigSend(sess *session.Session, g *session.Grant, sizes []int, d
 			// Echo the intended size into the payload so a truncated/fragmented arrival is
 			// still attributable to the size we meant to send.
 			binary.BigEndian.PutUint32(payload[0:4], uint32(size))
+			// [8:16]: the action id, as on every granted packet (spec §5 correlation).
+			putActionID(payload, g.ActionID)
 			err := s.sendErr(conn, target, sess, TypeBigSend, uint32(i), payload)
 			results = append(results, BigSendResult{
 				SizeBytes: size, Seq: i, Sent: err == nil, Err: errString(err),

server/internal/dataplane/throughput.go

@@ -120,7 +120,7 @@ func (s *Server) DownThroughput(
 
 	// Same plan the grant was sized from, so the two cannot disagree.
 	durationMs, kbps = ThroughputPlan(durationMs, kbps)
-	if sizeBytes < HeaderSize+16 {
+	if sizeBytes < HeaderSize+24 {
 		sizeBytes = 1200 // a size that survives every common path unfragmented
 	}
 	if sizeBytes > 1472 {
@@ -134,6 +134,10 @@ func (s *Server) DownThroughput(
 	}
 
 	payload := make([]byte, sizeBytes-HeaderSize)
+	// [8:16]: the action id, as on every granted packet (spec §5 correlation). The send
+	// timestamp lives past it at [16:24]; the client reads only header fields today, so
+	// reserving the slot costs nothing and keeps one layout rule across granted types.
+	putActionID(payload, g.ActionID)
 	deadline := time.Now().Add(time.Duration(durationMs) * time.Millisecond)
 	start := time.Now()
 	next := start
@@ -157,7 +161,7 @@ func (s *Server) DownThroughput(
 		// Reaching here means the run is progressing normally; the clock will end it.
 		res.LimitedBy = "duration"
 		binary.BigEndian.PutUint32(payload[0:4], seq)
-		binary.BigEndian.PutUint64(payload[4:12], uint64(time.Since(s.start).Nanoseconds()))
+		binary.BigEndian.PutUint64(payload[16:24], uint64(time.Since(s.start).Nanoseconds()))
 		if err := s.sendErr(conn, target, sess, TypeThroughputData, seq, payload); err != nil {
 			// A send error mid-run is a local condition (buffer full, route gone). Stop and
 			// report what got out rather than pretending the rest was lost on the path.

server/internal/dataplane/tos_linux.go

@@ -0,0 +1,55 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build linux
+
+package dataplane
+
+import (
+	"net"
+	"syscall"
+)
+
+// withTOS runs fn with the socket's TOS/traffic class set to dscp<<2 (ECN bits left zero — the
+// test is about DSCP survival, and claiming ECN capability we do not use would pollute it), then
+// restores what was there before.
+//
+// Same borrow discipline as withDF: the socket is shared by every session on that family, so the
+// caller must hold Server.dfMu for the whole window or a concurrent burst rides along with — or
+// clears — someone else's marking.
+func withTOS(conn *net.UDPConn, dscp int, fn func() error) error {
+	raw, err := conn.SyscallConn()
+	if err != nil {
+		return err
+	}
+	v4 := conn.LocalAddr().(*net.UDPAddr).IP.To4() != nil
+	level, opt := syscall.IPPROTO_IPV6, syscall.IPV6_TCLASS
+	if v4 {
+		level, opt = syscall.IPPROTO_IP, syscall.IP_TOS
+	}
+
+	var setErr error
+	prev := 0
+	if err := raw.Control(func(fd uintptr) {
+		if p, e := syscall.GetsockoptInt(int(fd), level, opt); e == nil {
+			prev = p
+		}
+		setErr = syscall.SetsockoptInt(int(fd), level, opt, dscp<<2)
+	}); err != nil {
+		return err
+	}
+	if setErr != nil {
+		return setErr
+	}
+	defer func() {
+		_ = raw.Control(func(fd uintptr) {
+			_ = syscall.SetsockoptInt(int(fd), level, opt, prev)
+		})
+	}()
+	return fn()
+}
+
+// TOSSupported reports whether withTOS can actually mark packets here. Exported so the control
+// plane can tell the client up front that its dscp request will not be honored, instead of the
+// client measuring an unmarked burst and concluding the network stripped the marking.
+const TOSSupported = true

server/internal/dataplane/tos_other.go

@@ -0,0 +1,16 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build !linux
+
+package dataplane
+
+import "net"
+
+// Setting DSCP per-burst uses IP_TOS/IPV6_TCLASS under the same fd-borrow pattern as withDF,
+// which is only exercised on Linux deployments. Elsewhere the burst goes out with the default
+// class and TOSSupported lets the action response say so — an unmarked burst reported as marked
+// would read as "the network stripped DSCP", the exact wrong conclusion.
+func withTOS(_ *net.UDPConn, _ int, fn func() error) error { return fn() }
+
+const TOSSupported = false

server/internal/dataplane/train.go

@@ -0,0 +1,122 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package dataplane
+
+// Upstream trains (spec §3.2, types 0x03–0x05). The client blasts TRAIN_DATA at the server and
+// the server answers nothing per-packet — a reply would double the traffic and measure the
+// return path at the same time. Afterwards the client asks for the server's received view with
+// TRAIN_REPORT_REQ, and gets it back columnar, split across as many TRAIN_REPORT datagrams as
+// it takes to stay under a safe size.
+//
+// Both TRAIN_DATA and TRAIN_REPORT_REQ carry the train id in payload[0:4]; the id is the
+// client's to choose, unique within the session.
+
+import (
+	"encoding/binary"
+	"net"
+	"net/netip"
+
+	"echo-lot.app/server/internal/session"
+)
+
+const (
+	// trainReportMaxDatagram caps one TRAIN_REPORT datagram at a size that survives every common
+	// path unfragmented. A report about loss must not itself be lost to MTU.
+	trainReportMaxDatagram = 1200
+	trainReportHeader      = 16
+	trainReportRow         = 17 // 4 seq + 8 t_rx_ns + 2 size + 1 ttl + 1 dscp + 1 ecn
+)
+
+// recordTrain buffers one TRAIN_DATA packet into its train (session-side, bounded — see
+// session/train.go). A payload too short to carry the id is unreportable and stays only in the
+// flat packet log, which already recorded it.
+func recordTrain(sess *session.Session, payload []byte, seq uint32, size int, tRxNs int64, meta pktMeta) {
+	if len(payload) < 4 {
+		return
+	}
+	sess.RecordTrainPacket(binary.BigEndian.Uint32(payload[0:4]), session.TrainEntry{
+		Seq: seq, TRxNs: tRxNs, Size: uint16(min(size, 0xFFFF)),
+		TTL: meta.TTL, DSCP: meta.dscp(), ECN: meta.ecn(),
+	})
+}
+
+// trainReport answers one TRAIN_REPORT_REQ with the full columnar report.
+//
+// Grant-free on purpose. §3.4 caps ungranted responses at the request size, and a multi-part
+// report is larger than the single REPORT_REQ that asked for it — but it cannot amplify: every
+// 17-byte row accounts for one HMAC-valid TRAIN_DATA packet of at least HeaderSize+4 bytes this
+// session already delivered here, so the whole report is a strict fraction of the traffic it
+// describes, and it only ever goes to the session's verified source address. An unknown id gets
+// a single zero-row report rather than silence — "nothing arrived" IS the measurement.
+func (s *Server) trainReport(conn *net.UDPConn, raddr netip.AddrPort, sess *session.Session, payload []byte) {
+	if len(payload) < 4 {
+		return
+	}
+	id := binary.BigEndian.Uint32(payload[0:4])
+	train, _ := sess.TrainView(id)
+	train.ID = id
+	for i, part := range buildTrainReport(train) {
+		s.send(conn, raddr, sess, TypeTrainReport, uint32(i), part)
+	}
+}
+
+// buildTrainReport lays a train's received view out columnar and cuts it into datagram-sized
+// payloads. Layout (mirrored by the client; all big-endian):
+//
+//	 0  4  train_id
+//	 4  4  received       (every packet counted, buffered or not — loss math uses this)
+//	 8  2  part           (0-based)
+//	10  2  parts
+//	12  1  flags          (bit0: buffer overflowed; rows beyond the cap were counted, not kept —
+//	                       the schema's evidence_truncated honesty, on the wire)
+//	13  1  reserved
+//	14  2  n              (rows in this part)
+//	16     n×4 seq, n×8 t_rx_ns, n×2 size, n×1 ttl, n×1 dscp, n×1 ecn (columns contiguous)
+func buildTrainReport(t session.Train) [][]byte {
+	perPart := (trainReportMaxDatagram - HeaderSize - trainReportHeader) / trainReportRow
+	parts := (len(t.Entries) + perPart - 1) / perPart
+	if parts == 0 {
+		parts = 1 // an empty train still gets its "received: 0" answer
+	}
+	out := make([][]byte, 0, parts)
+	for p := 0; p < parts; p++ {
+		rows := t.Entries[p*perPart : min((p+1)*perPart, len(t.Entries))]
+		n := len(rows)
+		b := make([]byte, trainReportHeader+n*trainReportRow)
+		binary.BigEndian.PutUint32(b[0:4], t.ID)
+		binary.BigEndian.PutUint32(b[4:8], uint32(t.Received))
+		binary.BigEndian.PutUint16(b[8:10], uint16(p))
+		binary.BigEndian.PutUint16(b[10:12], uint16(parts))
+		if t.Truncated {
+			b[12] = 1
+		}
+		binary.BigEndian.PutUint16(b[14:16], uint16(n))
+		off := trainReportHeader
+		for i, r := range rows {
+			binary.BigEndian.PutUint32(b[off+i*4:], r.Seq)
+		}
+		off += n * 4
+		for i, r := range rows {
+			binary.BigEndian.PutUint64(b[off+i*8:], uint64(r.TRxNs))
+		}
+		off += n * 8
+		for i, r := range rows {
+			binary.BigEndian.PutUint16(b[off+i*2:], r.Size)
+		}
+		off += n * 2
+		for i, r := range rows {
+			b[off+i] = r.TTL
+		}
+		off += n
+		for i, r := range rows {
+			b[off+i] = r.DSCP
+		}
+		off += n
+		for i, r := range rows {
+			b[off+i] = r.ECN
+		}
+		out = append(out, b)
+	}
+	return out
+}