# Echolot — build status & next steps

Last updated: 2026-07-29.

## Decided
- Name **Echolot**; domain echo-lot.app; scheme `echolot://`; namespace `app.echo_lot.*`
  (hyphen→underscore; appIds/packages can't contain hyphens). Prober appId `app.echo_lot.prober`.
- Stack: native **Kotlin + Jetpack Compose**, no Flutter.
- Tiers: `app` (no root), **`shizuku` in v1** (wireless-ADB pairing), `root` future.
- **License (decided 2026-07-30):** all code **GPL-3.0-or-later**; the specs in `docs/` **CC-BY-4.0**.
  Rationale: the moat is the no-root platform research, which is trivially liftable into a
  proprietary repackage — copyleft is the only option that prevents that, and the F-Droid /
  network-engineer audience reads GPL as a trust signal rather than friction. The specs go
  permissive on purpose: a wire protocol only becomes a standard if anyone can implement it.
  **Not AGPL for the server** — the ASP loophole it closes is speculative here, while blanket
  corporate AGPL bans would hit exactly the enterprise network teams most likely to self-host.
  Sole copyright holder, so relicensing the server to AGPL later stays possible.
  Open: substitute a real legal copyright holder for "Echolot contributors" in the SPDX headers.

## Specs (in `docs/`, alongside this file)
- `feature-catalog-and-feasibility.md`, `measurement-schema.md`, `probe-protocol.md`. Considered draft-complete and reviewed by the user.

## Capability prober — DELIVERED (as zip, 2026-07-29)
Full Kotlin/Compose project scaffolded: `app.echo_lot.prober`, minSdk 26 / target+compile 35,
AGP 8.7.3, Kotlin 2.0.21, Compose BOM 2024.10, Shizuku api+provider 13.1.5, kotlinx-serialization.
Probes implemented: `link.snapshot`, `icmp.ping4/6` (unprivileged ICMP datagram), `sockopt.matrix`
(TTL/TOS/RECVERR/MTU_DISCOVER), `trace.errqueue_reachable`, `multinetwork.request_and_bind`,
`local.mdns_discover`, `peer.ble_advertise`, `shizuku.command_battery` (ip neigh / ip -6 route /
ip addr / ip monitor / dumpsys network_stack DHCP+IpClient / dumpsys wifi). JSON export via share
intent; results carry verdict + raw evidence.

Could NOT be compiled in the cloud sandbox: dl.google.com (Google Maven) and services.gradle.org
are proxy-blocked, and no device is reachable for on-device runs. Build + iterate locally
(Android Studio / Claude Code). Wrapper is pinned to Gradle 8.14.3.

## Website — `web/` (2026-07-30, LIVE at https://echo-lot.app)
Single-page site for echo-lot.app on Cloudflare Workers: static `public/` from the edge, a small
Worker for the stable short URLs (`/apk`, `/apk.sha256`, `/fdroid`, `/source`) and `/api/latest`.
Version info is resolved from the Gitea releases API at request time (edge-cached 5 min), so
tagging a release is the only publish step — the homepage shows the latest version/date/size via
progressive-enhancement JS and falls back to pre-release copy otherwise. Auto light/dark via
`prefers-color-scheme`: dark = sonar display, light = chart-recorder printout, same amber-accent
token system. Deploy: `npx wrangler deploy` from `web/`, or CI via
`.gitea/workflows/deploy-site.yml` (needs `CLOUDFLARE_API_TOKEN` + `CLOUDFLARE_ACCOUNT_ID`
secrets); full story in `web/README.md`. Branding applied (2026-07-30): real favicon/wordmark
copied into `web/public/assets/` (copies — `assets/branding/` is the source of truth), palette
switched to abyss/teal/amber with teal-as-instrument semantics, sonar-sweep hero replaced by a
Focus-lattice panel (rogue-DHCP finding vignette), tagline "measure, don't guess".

## Branding — `assets/branding/` (2026-07-30)
Identity chosen: the **Focus** mark — a quiet lattice of nodes with exactly one under examination
(amber) inside teal viewfinder brackets. Tone is surgical measurement, not scanning (sonar-sweep
visuals and the "sound out your network" tagline were explicitly rejected); tagline is
**"measure, don't guess"**. Palette: abyss `#071522`, tile `#0E2433`, instrument teal `#35E0C4`,
finding amber `#FFB454`, foam `#E8F4F2` — teal is always the instrument, the single amber point is
the finding. The wordmark is hand-drawn monoline SVG paths (zero font dependency); the second "o"
is the signature teal ring + amber ping. Assets: `icon.svg` (+ `icon.png` 512² — Gitea avatars reject SVG), `icon-adaptive-{foreground,background}.svg`
(108dp adaptive-icon layers, art inside the 66dp safe circle), `wordmark-on-{dark,light}.svg`,
`banner.svg` (1200×300, wired into the repo README), `social-preview.svg`/`.png` (1280×640, for the
Gitea/GitHub social-preview slot). The website's placeholder favicon/wordmark can now be replaced
from these.

## First device report — OnePlus 15, Android 16/SDK 36 (2026-07-30)
Archived at `echolot-prober/reports/CPH2747-android16-sdk36.json`. Collection workflow that works:
deploy over (wireless) adb, but the **user** starts the run and exports the JSON manually — probe
runs reliably kill the adb-over-wifi session (multinetwork/multicast churn the link adb rides on).

OS findings:
- `link.snapshot`, `icmp.ping4` (38 ms), `sockopt.matrix` 4/4, `peer.ble_advertise`: SUPPORTED.
- **`trace.errqueue_reachable` SUPPORTED** — full Os-API errqueue path exists on Android 16;
  the C-over-JNI shim (next-steps #2) may be unnecessary on modern devices. Still needs a real
  errqueue round-trip test, and older devices may differ.
- `icmp.ping6` EAGAIN — topology, not capability: wifi was v4-only, v6 only on cellular, socket
  used the default network. Probe should bind per-network (also covers the ping4 case properly).
- `shizuku.command_battery` SUPPORTED, shell(2000): real `ip -6 route` RA data (lifetimes,
  per-table), `ip monitor` NEIGH events, wifi dump with full DhcpResults. Vendor formats look
  parseable.
- `local.mdns_discover`: lock acquired, discovery ran, 0 services in the 4 s window — needs a
  longer window / known-good reference network before calling it more than formally SUPPORTED.

Prober bugs the run exposed (all fixed same day):
- rotation wiped results + cancelled runs → state moved to a ViewModel;
- `multinetwork.request_and_bind` ERROR → missing `CHANGE_NETWORK_STATE` in the manifest;
- `rtt_ms: "38,1"` → device locale leaked into report numbers, now `Locale.ROOT`;
- 3/7 Shizuku commands `SHIZUKU_BIND_TIMEOUT` → bind/unbind-per-command raced Shizuku; now one
  bind per battery (`execBatch`).
Run 2 (same device, fixed APK — `…-run2.json`) confirmed all three fixes:
- `multinetwork.request_and_bind` **SUPPORTED** — wifi + cellular acquired and bound concurrently
  (downKbps 39094 / 13231); requesting cellular even brought up a second, dual-stack PDN
  (`rmnet_data2`, private v4 /30 + carrier-NAT DNS) next to the IPv6-only default PDN — exactly
  the per-network behavior the production app needs.
- Shizuku battery **7/7** in 2.9 s (was 4/7 in 34 s): full ARP/NDP neighbor table, `ip addr`,
  IpClient ProvisioningConfiguration incl. SSID/BSSID and APF caps (v6000, 4096 B).
- `rtt_ms: "32.0"` — locale fix holds.
Still open (probe improvements, not blockers): ping6 should bind per-network (still EAGAIN via
v4-only default wifi); mDNS window too short to see real services (0 found on a network that has
them); `ip monitor` 2 s window caught nothing on a quiet net — consider longer/event-triggered
capture; IP_MTU read via getsockoptInt reflection unavailable — reader belongs in the errqueue
shim if that lands.

## Go server skeleton — `server/` (2026-07-30)
Pure-Go stdlib implementation of the spec's core: control plane (enroll with single-use tokens,
profile with SPKI pin, sessions with the §2.4 HKDF key schedule) + UDP data plane (ELT1 header,
HMAC gate, 1024-wide anti-replay, ECHO_RESP with observation block, TIMESYNC, §3.4
anti-amplification). Wire format covered by `go test` (roundtrip, replay/bad-HMAC/unknown-prefix
silent drops); full enroll→profile→session flow smoke-tested live. Two run modes: **container**
(autodetected via /.dockerenv etc. or `--docker`; config from `ECHOLOT_*` env; distroless image,
`network_mode: host` required — Docker NAT would falsify the observed sources the protocol
measures) and **native** (`--install-systemd`/`--uninstall-systemd`, opt-in `--self-update`
against a Gitea releases API). CI: `.gitea/workflows/build-server.yml` — tests on push;
`server-v*` tags push the image to the Gitea registry + attach linux amd64/arm64 binaries that
self-update consumes. Not yet: TCP/TLS echo, STUN, canary DNS, actions, observations API,
real admin UI, self-update signature verification.

Prober build numbering: ascending `versionCode` shown on screen + as `proberBuild` in the JSON
report; current deployed build = **3**. Bump on every deployed change.

## Build-2 reports: OnePlus 15 (A16) + Lenovo TB330FU (A15) — 2026-07-30
Archived as `…-build2.json` in `echolot-prober/reports/`. The findings:
- **`traceroute.udp4` SUPPORTED on BOTH devices** (SDK 35 + 36): 6 real hops via pure-Kotlin
  `Os.recvmsg(MSG_ERRQUEUE)` in ~250 ms, identical paths (A1 → Cloudflare). **The C-over-JNI
  errqueue shim is dead** for Android 15+; keep it in mind only if pre-15 devices matter.
- Per-network ICMP works as designed: phone ping6 = "cellular only, default has no v6 path"
  (SUPPORTED with topology evidence instead of the old bare ERROR); per-network RTTs
  (wifi 20 ms vs cellular 201 ms on v4).
- **Network finding (dogfood!): hudeWLAN advertises a v6 default route via RA but hands out no
  global v6 address** — both devices have only link-local + a ::/0 route on wifi. That's a
  half-broken IPv6 config on the LAN, exactly the class of issue the product should flag.
- mDNS: meta-query returns 0 on BOTH devices (NsdManager limitation, now confirmed twice);
  concrete `_http._tcp` finds 4 real services (3× "Magic 2 LAN", EPSON WF-7840) on both.
  Production inventory must enumerate concrete types, not trust the meta-query.
- Tablet Shizuku: binder alive, permission granted, but UserService bind timed out (0/7) —
  first-spawn dex extraction on slow storage suspected; build 3 raises the bind window to
  25 s + one retry. Phone stays 7/7 with rich neighbor/RA/DHCP evidence.
  **Build-3 verdict: not timing.** Both 25 s attempts timed out (50 s total) — the UserService
  spawn genuinely fails on the Lenovo/A15. Build 4 adds a reflection fallback to the legacy
  `Shizuku.newProcess` remote-process API when the bind fails; `exec_path` in the evidence says
  which path ran. Whatever the outcome, core-shizuku must not assume UserService works
  everywhere. (Phone build 3: still 7/7; `ip_monitor` now catches provoked NEIGH
  PROBE→REACHABLE transitions, and a mid-path router dropping one TTL round showed the "*"
  hop path works in traceroute.udp4.)

  **Build-4 verdict (`…-build4.json`): the fallback WORKS.** Tablet Shizuku now SUPPORTED via
  `exec_path: newProcess fallback` — 6/7 commands with real data (full neighbor table, per-netId
  v6 route tables, Lenovo's IpClient dump — a distinctly different format from OnePlus's, i.e.
  the per-vendor parser sample we wanted). **core-shizuku design consequence: dual-path executor
  is mandatory** — UserService where it binds, newProcess where it doesn't; both confirmed live
  on real hardware. Known rough edges: `ip monitor` times out under newProcess (subshell trick
  doesn't survive that path); the 2×25 s bind wait before falling back is worth shortening once
  a device is known-bad. Tablet UserService root cause still open — multi-user (3 users) is the
  prime suspect; Shizuku app is current (13.6.0), so the stale-app theory is dead.
- `ip_monitor` returned no events this run even with the provoked gateway ping (gateway was
  already REACHABLE, so no NEIGH transition happened). Evidence-dependent, not a bug.

## Pipeline shakeout — 2026-07-30, partially done
Repo pushed to git.rambossek.at/EchoLot/echolot (ssh :2222). Actions runner works:
`server-test` green on push. `server-v0.1.0` release shipped with all assets
(`echolot-server_linux_{amd64,arm64}` + `SHA256SUMS`) after two workflow fixes: mixed
paths+tags triggers never fire (split into test-server.yml / build-server.yml), and a greedy
`sed` grabbed a nested user id instead of the release id → uploads 404ed (first-match grep now;
release creation also falls back to GET-by-tag on re-runs). Binaries verified downloadable →
`--self-update` has its artifact source. **Image job green too** on the dedicated
`compilesau-echolot` runner (label `echolot`): needed a PAT with package read/write as the
`REGISTRY_TOKEN` repo secret — the built-in Actions token is rejected by the container
registry. `git.rambossek.at/echolot/echolot-server:{v0.1.0,latest}` pulls anonymously
(3.9 MB distroless, verified). Full chain proven: tag → tests → binaries → release assets →
registry image → anonymous pull. Note the tag convention: image tags carry the bare version
(`v0.1.0`), release tags the namespaced one (`server-v0.1.0`); selfupdate normalizes.

## Toolchain upgrade + build-5 tablet re-run (2026-07-30)

Moved to the laptop (USB adb — far more stable than wireless, as expected). Upgraded the build
off the JDK-21 ceiling: **AGP 8.7.3 → 9.2.0, Gradle 8.14.3 → 9.6.0, Kotlin 2.0.21 → 2.2.10**,
which lets the toolchain run on JDK 25. Two AGP-9 migration edits were required:
- AGP 9 has **built-in Kotlin support**, so applying `org.jetbrains.kotlin.android` alongside it
  fails with "extension with name 'kotlin' already registered" — the alias must be dropped
  (`kotlin.compose` / `kotlin.serialization` stay; they are separate compiler plugins).
- The `kotlinOptions { jvmTarget }` block came from that plugin and no longer resolves; AGP
  derives jvmTarget from `compileOptions` instead.

`compileSdk`/`targetSdk` 35 → 36, because Android Studio only ships API 36.1 by default and
installing 35 was avoidable churn. **Build-5 re-run on the TB330FU is verdict-identical to
build-4 across all 10 probes** (`…-build5.json`) — the toolchain jump and targetSdk 36 are
behaviour-neutral on this device, including the `newProcess` Shizuku fallback (still 7/7,
`exec_path: newProcess fallback`, UserService still never binds).

Also of note: `traceroute.udp4` is SUPPORTED here (6 hops via errqueue, "no native shim needed"),
which is what retires next-step 2 below — the JNI shim is not required on either known device.

**OnePlus 15 build-5 re-run (`CPH2747-android16-sdk36-build5.json`): all 10 SUPPORTED, identical
to build-3.** `exec_path: UserService` on the phone vs `newProcess fallback` on the tablet, both
7/7 — the dual-path executor requirement is now confirmed on the current toolchain on both
devices. Phone is on Android 16 / SDK 36, i.e. `targetSdk = 36` is also exercised natively there.

Two collection-loop gotchas found while driving the phone over USB:
- **`icmp.ping6`'s verdict is topology-dependent, not build-dependent.** A first run with Shizuku
  stopped and only 2 networks up reported UNSUPPORTED; with cellular+wifi present it is the
  expected SUPPORTED / "echo reply on cellular only — default network has no v6 path". Do not
  read a ping6 verdict without checking `link.snapshot`'s `network_count` in the same report.
- **The Shizuku permission dialog times out after 30 s** (`shizuku.command_battery` logs
  `Shizuku permission not granted` at ~30027 ms). Screenshot→read→tap round-trips can exceed
  that. Grant the permission *before* starting a run, or accept that the first run after a fresh
  install burns the Shizuku probe; the grant is persistent, so the next run is clean.
- The phone auto-rotates; tap coordinates must be recomputed per orientation, and `uiautomator
  dump` can report a stale idle state right after a tap — trust the exported JSON's `durationMs`
  values as ground truth for whether a run really completed, not the button label.

## Next steps
1. Build locally, run on several physical devices (varied Android versions/vendors), collect the
   JSON reports — especially the real per-device Shizuku dump formats.
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.
4. Fold confirmed capabilities into the production `core-probe` / `core-shizuku` modules.

## Production probe server — LIVE on dedicated VM "fmr" (2026-07-31)
`echolot-server v0.2.0` runs natively (systemd, no docker) on a dedicated VM: 2×IPv4 + 2×IPv6
service addresses (fmr-1/fmr-2.echo-lot.app, dual-stack DNS), a third IPv6 (`::2`) reserved for
SSH only — verified untouched by the daemon (explicit multi-address binds, no wildcard).
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).
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)
Shipped and deployed to fmr via the server's own `--self-update` (first real exercise:
checksum-verified download v0.2.0→v0.3.0, atomic replace, restart — worked). Added over v0.2.0:
- **STUN** (RFC 5389 + 5780): 4 service addrs × primary/alt-port grid. Externally verified on
  v4 AND v6 — binding success with XOR-MAPPED, RESPONSE-ORIGIN, OTHER-ADDRESS present, so the
  profile now advertises **`stun-5780`** (the second IP earns its keep).
- **TCP echo** (:8441): JSON greeting with observed src + real Linux TCP_INFO — verified
  externally `mss:1440` (v6, 1500−60), options `[sack,wscale]`, then byte-echo.
- **Observations API** `GET /v1/sessions/{id}/observations` (per-packet UDP view, connect-back
  results, TCP records correlated by source IP).
- **Actions** `POST /v1/sessions/{id}/actions`: `delayed_echo` (DELAYED_ECHO at the observed
  data-plane source — NAT-lifetime primitive) and `connect_back` (dials the control-plane
  source, records connected/refused/timeout+rtt).
- Capabilities computed from what's actually wired: `udp-probe, delayed-echo, connect-back,
  tcp-echo, stun-5780`.
Still not implemented: TLS-echo/JA4, HTTP echo, tls-reference, canary DNS (§6.1 reference
records), and the train/big-send/frag/throughput actions. Admin UI still token-mint + health only.

## Canary DNS live — server v0.3.1 on fmr (2026-07-31)
Zone `c.echo-lot.app` delegated (NS → fmr-1/fmr-2) and authoritative on all 4 service IPs
udp+tcp/53. Verified through full public recursion: `ttl-5` A→192.0.2.5 (Cloudflare), `ttl-3600`
AAAA→2001:db8::3600 (Google), `big-txt` TXT returned (TCP fallback, truncated over UDP as
designed). End-to-end session attribution works: a `<nonce>.<session-prefix>.c.echo-lot.app`
query resolved via a public resolver shows up in `GET /v1/sessions/{id}/observations` →
`dns_canary` with the resolver's real egress IP, transport, and EDNS. First real test already
caught a finding: **Google applies 0x20 case randomization** (mixed-case qname), Cloudflare does
not — captured via `case_preserved`. Capabilities now: udp-probe, delayed-echo, connect-back,
tcp-echo, stun-5780, canary-dns. Kept the hand-rolled stdlib DNS (no miekg/dns) — validated
against independent clients. Deployed via `--self-update` (v0.3.0→v0.3.1, checksum-verified).

## Server v0.3.2 + v0.3.3 (2026-07-31)
- **v0.3.2 — control-plane security (live on fmr, externally verified):** `POST /v1/echo`
  reflects the received request head+body (b64) and observed TLS (version/cipher/SNI/ALPN) —
  captured real SNI `fmr-1.echo-lot.app` and an injected header over public TLS1.3; `GET
  /v1/tls-reference` returns the served DER chain + pin (cross-checked against the openssl-derived
  pin). Optional cleartext echo listener (default off). Capability `http-echo`.
- **v0.3.3 — MTU probe (data plane):** MTU_PROBE (0x09) → small MTU_ACK (0x0A) carrying the
  received datagram size; client DF-probes increasing sizes to find path MTU / black holes. ACK
  is tiny → never amplifies. Tested.
- **Note on trains:** upstream trains (TRAIN_DATA 0x03) are already observable — every HMAC-valid
  packet is recorded (seq/t_rx/size/type) with no per-packet response, so loss/reordering/inter-
  arrival are visible via GET observations. The dedicated data-plane TRAIN_REPORT (0x05) is
  deferred: §3.4 anti-amplification means it needs an asymmetric grant + columnar multi-datagram
  encoding — a focused batch, not a corner to rush.
Remaining spec: tls-echo (ClientHello+JA4), TRAIN_REPORT, big/frag-send, throughput, downtrain;
real admin UI.

## Server self-test + host tuning — v0.3.4/v0.3.5, fmr proven good (2026-07-31)
The daemon now proves its own host is a clean measurement target:
- **sysctl audit** (`GET /admin/selftest`, startup warnings): on first run it flagged exactly 4
  real issues on fmr — accept_ra=1 on a static-v6 host, accept_redirects=1, send_redirects=1,
  icmp_ratelimit=1000. Recommended `server/deploy/99-echolot-sysctl.conf` applied (v6 default
  route/addrs are proto static with 0 RA-derived routes, so disabling accept_ra is safe —
  verified v6 egress intact after). Now sysctl_ok=true, 0 warnings.
- **egress-MTU self-proof**: DF PMTUD via IP_MTU_DISCOVER + getsockopt IP_MTU (v0.3.4 had a bug —
  read IP_MTU without connecting → ENOTCONN; v0.3.5 connects first). fmr reports 1500 on both v4
  and v6 → mtu_ok=true, so client MTU tests are trustworthy.
- Both signals ride in the profile as `server_selftest{mtu_ok,sysctl_ok}` so a client can skip
  MTU testing when the server can't support it honestly.
fmr profile now: `{mtu_ok: true, sysctl_ok: true}`.

## Server v0.3.6 — tls-echo / JA4: spec §4 COMPLETE (2026-07-31)
The elt-echo TLS variant runs on the TCP-echo port (8441), multiplexed by a timed 0x16 peek
(plain echo stays server-speaks-first; a TLS ClientHello routes to the TLS path). It captures
the full ClientHello, returns it raw (b64) + as a JA4 fingerprint (FoxIO), then TLS byte-echoes —
the sec.clienthello_echo evidence. Hand-rolled ClientHello parser (ciphers/exts/ALPN/
supported_versions/sig-algs, GREASE-excluded), unit-tested. **Cross-client verified on fmr**:
openssl → t13d3013eo (30 ciphers), python ssl → t13d1712eo (17) — different stacks, different
fingerprints, correct _a structure both. Capability tls-echo.

Spec §4 (TCP/TLS/HTTP/STUN) is now fully implemented. Server capabilities: udp-probe,
delayed-echo, connect-back, http-echo, tcp-echo, tls-echo, stun-5780, canary-dns.
Remaining spec: §5 heavy actions (downtrain/big_send/frag_send/throughput) + the TRAIN_REPORT
retrieval path — all gated on the anti-amplification grant machinery (§3.4) — and a real admin UI.