server: STUN, TCP echo, observations API, delayed-echo + connect-back actions

- stun: RFC 5389 binding responder + RFC 5780 attributes (OTHER-ADDRESS, RESPONSE-ORIGIN, CHANGE-REQUEST) on a primary/alt-port socket grid per address; advertises stun-5780 with >=2 same-family addrs, else stun-basic. Unmodified framing for tooling interop. Tested. - tcpecho: JSON greeting with observed src + TCP_INFO MSS/options (Linux getsockopt; zeroed elsewhere via build tags), then byte echo. - session: per-packet UDP observations + connect-back results, ByID lookup. - control: GET /v1/sessions/{id}/observations, POST .../actions (delayed_echo → DELAYED_ECHO at the observed data-plane source; connect_back → dial the control-plane source, record connected/refused/ timeout+rtt). Capabilities computed from what is actually wired. - config/main: comma-separated STUN listeners; all planes bind explicit addresses; graceful shutdown of the new listeners. Full flow smoke-tested; go test green (stun binding/change-port, dataplane wire format). Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
build-status: production server v0.2.0 live on the fmr VM
2026-07-31 19:53:36 +02:00 · 2026-07-31 19:42:56 +02:00 · 2026-07-31 19:40:36 +02:00 · 2026-07-30 17:35:53 +02:00 · 2026-07-30 17:34:54 +02:00 · 2026-07-30 16:54:52 +02:00
21 changed files with 1576 additions and 83 deletions
@@ -1,7 +1,7 @@
 {
  "permissions": {
    "allow": [
-      "WebFetch(domain:open-vsx.org)"
+      "WebFetch(domain:open-vsx.org)",
      "WebFetch(domain:github.com)"
    ]
  }
@@ -63,23 +63,27 @@ First build downloads AGP/Compose/Shizuku from Google Maven + Maven Central.

 - **Prefer USB for adb.** Wireless debugging dies constantly: probe runs churn the wifi the
  debug link rides on, the Lenovo tablet's ZUI power management kills the listener anyway, and
-  the port rotates on every restart. Deploys over wireless work between runs; never drive a
-  probe run over adb.
- Collection loop that works: install over adb → the **user** runs the probes and exports the
-  JSON manually → archive it under `echolot-prober/reports/` and record findings in
-  `docs/build-status.md`.
+  the port rotates on every restart. Never drive a probe run over *wireless* adb.
+- Collection loop over USB, fully driveable by Claude: install → `am start` → tap "Run all
+  probes" → poll `uiautomator dump` until the button label returns to "Run all probes" → tap
+  "Export JSON" → the report lands in `cache/reports/` and comes back via
+  `adb shell run-as app.echo_lot.prober cat …` (no need to drive the share sheet; dismiss it
+  with BACK). Archive under `echolot-prober/reports/`, record findings in `docs/build-status.md`.
+- Bash-tool `adb shell` calls with absolute device paths get mangled by Git Bash path
+  conversion (`/data/…` → `C:/Program Files/Git/data/…`); use the PowerShell tool for those.
 - Bump `versionCode` on every deployed prober change — it shows on screen and as `proberBuild`
  in the report; that's how a report is matched to a build.
 - Known devices: OnePlus 15 (CPH2747, A16) — Shizuku UserService works;
  Lenovo TB330FU (A15, multi-user) — UserService never binds, the `newProcess` fallback carries
  it. Full history in build-status.md.
- Gradle needs JDK 17–21 (`JAVA_HOME`); a system JDK 25 breaks AGP 8.7. On machines with
-  Android Studio, its `jbr` directory works.
+- As of the AGP 9.2.0 / Gradle 9.6.0 / Kotlin 2.2.10 bump, JDK 17+ (including 25) works —
+  AGP 9 requires Gradle 9.1.0+ and Kotlin 2.2.10+ as its minimum KGP version. On machines with
+  Android Studio, its `jbr` directory works as `JAVA_HOME`.

 ## Likely next steps

 1. Run on physical devices; collect JSON reports across Android versions/vendors.
-2. If `trace.errqueue_reachable` is PARTIAL, add the C-over-JNI errqueue shim (recvmsg + cmsg parse)
-   as a `:native` module and a real `traceroute.udp4` probe.
+2. ~~C-over-JNI errqueue shim~~ — not needed; `trace.errqueue_reachable` and `traceroute.udp4`
+   are SUPPORTED on both known devices via `Os.recvmsg` + `StructMsghdr` reflection.
 3. Fold the confirmed capabilities + Shizuku dump-format samples back into the production
   `core-probe` / `core-shizuku` modules.
@@ -159,15 +159,68 @@ Repo pushed to git.rambossek.at/EchoLot/echolot (ssh :2222). Actions runner work
 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. **Still open: the `image` job** — needs a
-docker-capable runner (GITHUB_SERVER_URL inside the runner is the internal `http://app:3000`;
-set `ECHOLOT_REGISTRY_HOST=git.rambossek.at` as a repo variable/env when enabling it).
+`--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 (`recvmsg`+cmsg parse)
-   as a `:native` module and a real `traceroute.udp4` probe.
+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`.
@@ -1,21 +1,20 @@
 plugins {
    alias(libs.plugins.android.application)
-    alias(libs.plugins.kotlin.android)
    alias(libs.plugins.kotlin.compose)
    alias(libs.plugins.kotlin.serialization)
 }

 android {
    namespace = "app.echo_lot.prober"
-    compileSdk = 35
+    compileSdk = 36

    defaultConfig {
        applicationId = "app.echo_lot.prober"
        minSdk = 26
-        targetSdk = 35
+        targetSdk = 36
        // Bump versionCode on EVERY deployed change — it is shown on screen and lands in the
        // JSON report as proberBuild, so a report is attributable to an exact prober build.
-        versionCode = 4
+        versionCode = 5
        versionName = "0.1.0"
    }

@@ -28,9 +27,6 @@ android {
        sourceCompatibility = JavaVersion.VERSION_17
        targetCompatibility = JavaVersion.VERSION_17
    }
-    kotlinOptions {
-        jvmTarget = "17"
-    }
    buildFeatures {
        compose = true
        aidl = true
@@ -1,6 +1,6 @@
 [versions]
-agp = "8.7.3"
-kotlin = "2.0.21"
+agp = "9.2.0"
+kotlin = "2.2.10"
 coreKtx = "1.13.1"
 lifecycle = "2.8.7"
 activityCompose = "1.9.3"
@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.3-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.6.0-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME
@@ -0,0 +1,191 @@
+{
+    "schema": "echolot/prober-report",
+    "schemaVersion": "0.1.0",
+    "proberBuild": 5,
+    "device": {
+        "manufacturer": "OnePlus",
+        "model": "CPH2747",
+        "androidSdk": 36,
+        "androidRelease": "16"
+    },
+    "results": [
+        {
+            "id": "link.snapshot",
+            "title": "LinkProperties snapshot (all active networks)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "3 active network(s) read",
+            "evidence": {
+                "network_count": "3",
+                "net0.cellular.iface": "rmnet_data4",
+                "net0.cellular.mtu": "1500",
+                "net0.cellular.addrs": "2001:4bb8:417:bd78:e4fe:8cff:febe:ca8c/64",
+                "net0.cellular.dns": "fda1:3fb1:0:8:0:10:0:101, fda1:3fb1:0:8:0:10:0:100",
+                "net0.cellular.routes": "::/0 -> fe80::246f:12be:21ef:1b54 rmnet_data4 mtu 1500 | 2001:4bb8:417:bd78::/64 -> :: rmnet_data4 mtu 0",
+                "net0.cellular.domains": "",
+                "net0.cellular.nat64": "none",
+                "net0.cellular.private_dns": "off/opportunistic",
+                "net1.wifi.iface": "wlan0",
+                "net1.wifi.mtu": "0",
+                "net1.wifi.addrs": "fe80::bcf6:edff:fe67:b139/64, 10.13.102.122/24",
+                "net1.wifi.dns": "10.13.102.1",
+                "net1.wifi.routes": "fe80::/64 -> :: wlan0 mtu 0 | ::/0 -> fe80::7a9a:18ff:fe54:b8f9 wlan0 mtu 0 | 10.13.102.0/24 -> 0.0.0.0 wlan0 mtu 0 | 0.0.0.0/0 -> 10.13.102.1 wlan0 mtu 0",
+                "net1.wifi.domains": "hudelist.local",
+                "net1.wifi.nat64": "none",
+                "net1.wifi.private_dns": "off/opportunistic",
+                "net2.cellular.iface": "rmnet_data2",
+                "net2.cellular.mtu": "1500",
+                "net2.cellular.addrs": "10.73.62.113/30, 2001:4bb8:2fb:fe4c:f028:16ff:fee4:774d/64",
+                "net2.cellular.dns": "10.88.152.122, 10.88.152.123, fda1:3fb1:0:8:0:10:0:102, fda1:3fb1:0:8:0:10:0:103",
+                "net2.cellular.routes": "0.0.0.0/0 -> 10.73.62.114 rmnet_data2 mtu 1500 | ::/0 -> fe80::9419:9179:7ab7:1a1d rmnet_data2 mtu 1500 | 10.73.62.112/30 -> 0.0.0.0 rmnet_data2 mtu 0 | 2001:4bb8:2fb:fe4c::/64 -> :: rmnet_data2 mtu 0",
+                "net2.cellular.domains": "",
+                "net2.cellular.nat64": "none",
+                "net2.cellular.private_dns": "off/opportunistic"
+            },
+            "durationMs": 2
+        },
+        {
+            "id": "icmp.ping4",
+            "title": "ICMPv4 echo (unprivileged datagram socket)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "Echo reply on the default network",
+            "evidence": {
+                "default": "reply type=0 rtt_ms=79.3 bytes=22 target=1.1.1.1",
+                "net.cellular": "reply type=0 rtt_ms=180.5 bytes=22 target=1.1.1.1",
+                "net.wifi": "reply type=0 rtt_ms=39.7 bytes=22 target=1.1.1.1"
+            },
+            "durationMs": 304
+        },
+        {
+            "id": "icmp.ping6",
+            "title": "ICMPv6 echo (unprivileged datagram socket)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "Echo reply on cellular only — default network has no v6 path",
+            "evidence": {
+                "default": "error: recvfrom failed: EAGAIN (Try again)",
+                "net.cellular": "reply type=129 rtt_ms=53.8 bytes=22 target=2606:4700:4700::1111",
+                "net.wifi": "error: recvfrom failed: EAGAIN (Try again)"
+            },
+            "durationMs": 6308
+        },
+        {
+            "id": "sockopt.matrix",
+            "title": "Socket options: TTL, RECVERR, MTU_DISCOVER (DF)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "4/4 core sockopts accepted; IP_MTU read=false",
+            "evidence": {
+                "IP_TTL": "accepted (ttl=5)",
+                "IP_TOS/DSCP": "accepted (EF/46)",
+                "IP_RECVERR": "accepted",
+                "IP_MTU_DISCOVER=PROBE": "accepted (DF set)",
+                "IP_MTU(read)": "unreadable: android.system.Os.getsockoptInt [class java.io.FileDescriptor, int, int]"
+            },
+            "durationMs": 2
+        },
+        {
+            "id": "trace.errqueue_reachable",
+            "title": "Traceroute via IP_RECVERR + MSG_ERRQUEUE",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "Errqueue path fully reachable from Os API",
+            "evidence": {
+                "IP_RECVERR": "accepted",
+                "IP_TTL=1": "accepted",
+                "StructMsghdr": "true",
+                "Os.recvmsg": "true"
+            },
+            "durationMs": 1
+        },
+        {
+            "id": "traceroute.udp4",
+            "title": "UDP traceroute via MSG_ERRQUEUE (no root, no JNI)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "6 hop(s) read via errqueue — no native shim needed",
+            "evidence": {
+                "recvmsg_api": "StructMsghdr + Os.recvmsg via reflection",
+                "target": "1.1.1.1",
+                "hop.1": "10.13.102.1 icmp type=11 origin=2 ~41 ms",
+                "hop.2": "178.191.103.254 icmp type=11 origin=2 ~41 ms",
+                "hop.3": "195.3.76.32 icmp type=11 origin=2 ~41 ms",
+                "hop.4": "195.3.64.153 icmp type=11 origin=2 ~41 ms",
+                "hop.5": "172.68.48.30 icmp type=11 origin=2 ~41 ms",
+                "hop.6": "172.68.48.14 icmp type=11 origin=2 ~41 ms"
+            },
+            "durationMs": 248
+        },
+        {
+            "id": "multinetwork.request_and_bind",
+            "title": "Concurrent per-network binding (Wi-Fi / cellular / ethernet)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "2 transport(s) acquired and bound (only currently-present links can bind)",
+            "evidence": {
+                "wifi": "network acquired; bindSocket=ok; downKbps=27368",
+                "cellular": "network acquired; bindSocket=ok; downKbps=13231",
+                "ethernet": "no network within 4s"
+            },
+            "durationMs": 4013
+        },
+        {
+            "id": "local.mdns_discover",
+            "title": "Multicast reception (MulticastLock + mDNS/NSD)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "mDNS discovery ran; 4 service(s)/type(s) seen across 3 queries",
+            "evidence": {
+                "multicast_lock": "acquired",
+                "meta.started": "true",
+                "meta.found": "0",
+                "meta.type": "_services._dns-sd._udp.",
+                "http.started": "true",
+                "http.found": "4",
+                "http.names": "Magic 2 LAN 1-1, Magic 2 LAN triple #5, Magic 2 LAN triple #4, EPSON WF-7840 Series",
+                "http.type": "_http._tcp.",
+                "googlecast.started": "true",
+                "googlecast.found": "0",
+                "googlecast.type": "_googlecast._tcp."
+            },
+            "durationMs": 10005
+        },
+        {
+            "id": "peer.ble_advertise",
+            "title": "BLE peripheral advertising (peer-mode control channel)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "Advertising start: success",
+            "evidence": {
+                "FEATURE_BLUETOOTH_LE": "true",
+                "adapter_enabled": "true",
+                "multi_advertisement_supported": "true",
+                "startAdvertising": "success"
+            },
+            "durationMs": 29
+        },
+        {
+            "id": "shizuku.command_battery",
+            "title": "Shizuku shell tier (ip neigh / route / dumpsys network_stack)",
+            "tier": "SHIZUKU",
+            "verdict": "SUPPORTED",
+            "summary": "Shizuku runs as shell(2000); 7/7 commands returned data",
+            "evidence": {
+                "binder_alive": "true",
+                "version": "13",
+                "runs_as": "shell(2000)",
+                "permission": "true",
+                "exec_path": "UserService",
+                "id": "uid=2000\nuid=2000(shell) gid=2000(shell) groups=2000(shell),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),1078(ext_data_rw),1079(ext_obb_rw),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats),3009(readproc),3011(uhid),3012(readtracefs) context=u:r:shell:s0",
+                "ip_neigh": "uid=2000\n10.13.102.111 dev wlan0  FAILED\n10.13.102.50 dev wlan0 lladdr 50:57:9c:4f:7a:3c STALE\n10.13.102.31 dev wlan0 lladdr 98:5f:d3:f6:f1:75 STALE\n10.13.102.116 dev wlan0 lladdr 0c:08:b4:03:68:0e STALE\n10.13.102.120 dev wlan0 lladdr 0e:d8:14:58:6c:8b STALE\n10.13.102.5 dev wlan0 lladdr 90:09:d0:1a:83:e4 STALE\n10.13.102.1 dev wlan0 lladdr 78:9a:18:54:b8:f9 REACHABLE\n10.13.102.21 dev wlan0 lladdr c8:7f:54:01:94:7c STALE\nfe80::babe:f4ff:febc:caf9 dev wlan0 lladdr b8:be:f4:bc:ca:f9 REACHABLE\nfe80::7a9a:18ff:fe54:b8f9 dev wlan0 lladdr 78:9a:18:54:b8:f9 router STALE\nfe80::babe:f4ff:febc:cacf dev wlan0 lladdr b8:be:f4:bc:ca:cf REACHABLE\nfe80::babe:f4ff:fec2:bf14 dev wlan0 lladdr b8:be:f4:c2:bf:14 REACHABLE",
+                "ip6_route": "uid=2000\nfe80::/64 dev wlan0 table 1028 proto kernel metric 256 pref medium\nfe80::/64 dev wlan0 table 1028 proto static metric 1024 pref medium\ndefault via fe80::7a9a:18ff:fe54:b8f9 dev wlan0 table 1028 proto ra metric 1024 expires 1269sec pref medium\nfe80::/64 dev vgate0 table 1031 proto kernel metric 256 pref medium\n2001:4bb8:417:bd78::/64 dev rmnet_data4 table 1032 proto kernel metric 256 pref medium\n2001:4bb8:417:bd78::/64 dev rmnet_data4 table 1032 proto static metric 1024 pref medium\nfe80::/64 dev rmnet_data4 table 1032 proto kernel metric 256 pref medium\ndefault via fe80::246f:12be:21ef:1b54 dev rmnet_data4 table 1032 proto ra metric 1024 expires 64373sec hoplimit 255 pref medium\n2001:4bb8:2fb:fe4c::/64 dev rmnet_data2 table 1000000022 proto static metric 1024 pref medium\nfe80::/64 dev wlan0 table 1000000028 proto static metric 1024 pref medium\n2001:4bb8:417:bd78::/64 dev rmnet_data4 table 1000000032 proto static metric 1024 pref medium\nfe80::/64 dev dummy0 table 1002 proto kernel metric 256 pref medium\ndefault dev dummy0 table 1002 proto static metric 1024 pref medium\nfe80::/64 dev ifb0 table 1003 proto kernel metric 256 pref medium\nfe80::/64 dev ifb1 table 1004 proto kerne",
+                "ip_addr": "uid=2000\n1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000\n    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00\n    inet 127.0.0.1/8 scope host lo\n       valid_lft forever preferred_lft forever\n    inet6 ::1/128 scope host \n       valid_lft forever preferred_lft forever\n2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000\n    link/ether be:3d:e2:93:78:b9 brd ff:ff:ff:ff:ff:ff\n    inet6 fe80::bc3d:e2ff:fe93:78b9/64 scope link \n       valid_lft forever preferred_lft forever\n3: ifb0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc htb state UNKNOWN group default qlen 1000\n    link/ether ba:6e:46:b5:3d:bb brd ff:ff:ff:ff:ff:ff\n    inet6 fe80::b86e:46ff:feb5:3dbb/64 scope link \n       valid_lft forever preferred_lft forever\n4: ifb1: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc htb state UNKNOWN group default qlen 1000\n    link/ether d6:2a:e2:f5:93:8f brd ff:ff:ff:ff:ff:ff\n    inet6 fe80::d42a:e2ff:fef5:938f/64 scope link \n       valid_lft forever preferred_lft forever\n5: tunl0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN group default qlen 1000\n    link/ipip 0.0.0.0 brd 0.0.0.0\n6: gre0@NONE: <NO",
+                "ip_monitor": "uid=2000",
+                "dhcp_log": "uid=2000\nRecently active IpClient logs:\nIpClient.wlan0\n  IpClient.wlan0 APF dump:\n    Capabilities: { apfVersionSupported: 6000, maximumApfProgramSize: 4096 }\n    InstallableProgramSizeClamp: 2147483647\n--\n  IpClient.wlan0 current ProvisioningConfiguration:\n    ProvisioningConfiguration{mUniqueEui64AddressesOnly: false, mEnablePreconnection: false, mUsingMultinetworkPolicyTracker: true, mUsingIpReachabilityMonitor: true, mRequestedPreDhcpActionMs: 18000, mInitialConfig: null, mStaticIpConfig: null, mApfCapabilities: ApfCapabilities{version: 6000, maxSize: 4096, format: 1}, mProvisioningTimeoutMs: 18000, mIPv6AddrGenMode: 0, mNetwork: 171, mDisplayName: \"hudeWLAN\", mCreatorUid:1000, mScanResultInfo: SSID: hudeWLAN, BSSID: 24:5a:4c:5f:58:c5, Information Elements: {[ID: 0, [104, 117, 100, 101, 87, 76, 65, 78]][ID: 1, [-126, -124, -117, -106, 18, 36, 72, 108]][ID: 3, [6]][ID: 42, [0]][ID: 50, [12, 24, 48, 96]][ID: 45, [-83, 1, 23, -1, -1, -1, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 24, 4, -121, 25, 0]][ID: 61, [6, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]][ID: 48, [1, 0, 0, 15, -84, 4, 1, 0, 0, 15, -84, 4, 1, 0, 0, 15, -84, 2, 0, 0]][ID: 127, [0, 0, 8, -128, ",
+                "wifi_dump": "uid=2000\n rec[7]: time=07-30 16:23:27.779 processed=L2ConnectedState org=L3ConnectedState dest=<null> what=CMD_POST_DHCP_ACTION screen=on v4 v4r v4dns v6r\n rec[8]: time=07-30 16:23:27.784 processed=L2ConnectedState org=L3ConnectedState dest=<null> what=CMD_IPV4_PROVISIONING_SUCCESS screen=on DhcpResultsParcelable{baseConfiguration: IP address 10.13.102.122/24 Gateway 10.13.102.1  DNS servers: [ 10.13.102.1 ] Domains hudelist.local, leaseDuration: 600, mtu: 0, serverAddress: 10.13.102.1, vendorInfo: null, serverHostName: , captivePortalApiUrl: null}\n rec[9]: time=07-30 16:23:27.791 processed=ConnectableState org=L3ConnectedState dest=<null> what=CMD_UPDATE_LINKPROPERTIES screen=on 17 0 v4 v4r v4dns v6r\n rec[10]: time=07-30 16:23:47.971 processed=ConnectableState org=L3ConnectedState dest=<null> what=CMD_SCREEN_STATE_CHANGED screen=off 0 0\n--\n rec[31]: time=07-30 16:28:27.831 processed=L2ConnectedState org=L3ConnectedState dest=<null> what=CMD_POST_DHCP_ACTION screen=off v4 v4r v4dns v6r\n rec[32]: time=07-30 16:28:27.835 processed=L2ConnectedState org=L3ConnectedState dest=<null> what=CMD_IPV4_PROVISIONING_SUCCESS screen=off DhcpResultsParcelable{baseConfiguration: IP address 10.13.1"
+            },
+            "durationMs": 6000
+        }
+    ]
+}
@@ -0,0 +1,173 @@
+{
+    "schema": "echolot/prober-report",
+    "schemaVersion": "0.1.0",
+    "proberBuild": 5,
+    "device": {
+        "manufacturer": "LENOVO",
+        "model": "TB330FU",
+        "androidSdk": 35,
+        "androidRelease": "15"
+    },
+    "results": [
+        {
+            "id": "link.snapshot",
+            "title": "LinkProperties snapshot (all active networks)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "1 active network(s) read",
+            "evidence": {
+                "network_count": "1",
+                "net0.wifi.iface": "wlan0",
+                "net0.wifi.mtu": "0",
+                "net0.wifi.addrs": "fe80::416:b9ff:feac:5b65/64, 10.13.102.125/24",
+                "net0.wifi.dns": "10.13.102.1",
+                "net0.wifi.routes": "fe80::/64 -> :: wlan0 mtu 0 | ::/0 -> fe80::7a9a:18ff:fe54:b8f9 wlan0 mtu 0 | 10.13.102.0/24 -> 0.0.0.0 wlan0 mtu 0 | 0.0.0.0/0 -> 10.13.102.1 wlan0 mtu 0",
+                "net0.wifi.domains": "hudelist.local",
+                "net0.wifi.nat64": "none",
+                "net0.wifi.private_dns": "off/opportunistic"
+            },
+            "durationMs": 15
+        },
+        {
+            "id": "icmp.ping4",
+            "title": "ICMPv4 echo (unprivileged datagram socket)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "Echo reply on the default network",
+            "evidence": {
+                "default": "reply type=0 rtt_ms=104.5 bytes=22 target=1.1.1.1",
+                "net.wifi": "reply type=0 rtt_ms=24.2 bytes=22 target=1.1.1.1"
+            },
+            "durationMs": 135
+        },
+        {
+            "id": "icmp.ping6",
+            "title": "ICMPv6 echo (unprivileged datagram socket)",
+            "tier": "APP",
+            "verdict": "ERROR",
+            "summary": "No echo reply on any of 2 attempt(s)",
+            "evidence": {
+                "default": "error: recvfrom failed: EAGAIN (Try again)",
+                "net.wifi": "error: recvfrom failed: EAGAIN (Try again)"
+            },
+            "durationMs": 6125
+        },
+        {
+            "id": "sockopt.matrix",
+            "title": "Socket options: TTL, RECVERR, MTU_DISCOVER (DF)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "4/4 core sockopts accepted; IP_MTU read=false",
+            "evidence": {
+                "IP_TTL": "accepted (ttl=5)",
+                "IP_TOS/DSCP": "accepted (EF/46)",
+                "IP_RECVERR": "accepted",
+                "IP_MTU_DISCOVER=PROBE": "accepted (DF set)",
+                "IP_MTU(read)": "unreadable: android.system.Os.getsockoptInt [class java.io.FileDescriptor, int, int]"
+            },
+            "durationMs": 6
+        },
+        {
+            "id": "trace.errqueue_reachable",
+            "title": "Traceroute via IP_RECVERR + MSG_ERRQUEUE",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "Errqueue path fully reachable from Os API",
+            "evidence": {
+                "IP_RECVERR": "accepted",
+                "IP_TTL=1": "accepted",
+                "StructMsghdr": "true",
+                "Os.recvmsg": "true"
+            },
+            "durationMs": 5
+        },
+        {
+            "id": "traceroute.udp4",
+            "title": "UDP traceroute via MSG_ERRQUEUE (no root, no JNI)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "5 hop(s) read via errqueue — no native shim needed",
+            "evidence": {
+                "recvmsg_api": "StructMsghdr + Os.recvmsg via reflection",
+                "target": "1.1.1.1",
+                "hop.1": "10.13.102.1 icmp type=11 origin=2 ~44 ms",
+                "hop.2": "178.191.103.254 icmp type=11 origin=2 ~41 ms",
+                "hop.3": "195.3.76.32 icmp type=11 origin=2 ~44 ms",
+                "hop.4": "* (no errqueue event in 900 ms)",
+                "hop.5": "172.68.48.30 icmp type=11 origin=2 ~42 ms",
+                "hop.6": "172.68.48.14 icmp type=11 origin=2 ~42 ms"
+            },
+            "durationMs": 1140
+        },
+        {
+            "id": "multinetwork.request_and_bind",
+            "title": "Concurrent per-network binding (Wi-Fi / cellular / ethernet)",
+            "tier": "APP",
+            "verdict": "PARTIAL",
+            "summary": "1 transport(s) acquired and bound (only currently-present links can bind)",
+            "evidence": {
+                "wifi": "network acquired; bindSocket=ok; downKbps=30000",
+                "cellular": "no network within 4s",
+                "ethernet": "no network within 4s"
+            },
+            "durationMs": 8036
+        },
+        {
+            "id": "local.mdns_discover",
+            "title": "Multicast reception (MulticastLock + mDNS/NSD)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "mDNS discovery ran; 4 service(s)/type(s) seen across 3 queries",
+            "evidence": {
+                "multicast_lock": "acquired",
+                "meta.started": "true",
+                "meta.found": "0",
+                "meta.type": "_services._dns-sd._udp.",
+                "http.started": "true",
+                "http.found": "4",
+                "http.names": "Magic 2 LAN 1-1, Magic 2 LAN triple #5, Magic 2 LAN triple #4, EPSON WF-7840 Series",
+                "http.type": "_http._tcp.",
+                "googlecast.started": "true",
+                "googlecast.found": "0",
+                "googlecast.type": "_googlecast._tcp."
+            },
+            "durationMs": 10042
+        },
+        {
+            "id": "peer.ble_advertise",
+            "title": "BLE peripheral advertising (peer-mode control channel)",
+            "tier": "APP",
+            "verdict": "SUPPORTED",
+            "summary": "Advertising start: success",
+            "evidence": {
+                "FEATURE_BLUETOOTH_LE": "true",
+                "adapter_enabled": "true",
+                "multi_advertisement_supported": "true",
+                "startAdvertising": "success"
+            },
+            "durationMs": 74
+        },
+        {
+            "id": "shizuku.command_battery",
+            "title": "Shizuku shell tier (ip neigh / route / dumpsys network_stack)",
+            "tier": "SHIZUKU",
+            "verdict": "SUPPORTED",
+            "summary": "Shizuku runs as shell(2000); 6/7 commands returned data",
+            "evidence": {
+                "binder_alive": "true",
+                "version": "13",
+                "runs_as": "shell(2000)",
+                "permission": "true",
+                "exec_path": "newProcess fallback (UserService bind failed)",
+                "id": "uid=2000(shell) gid=2000(shell) groups=2000(shell),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),1078(ext_data_rw),1079(ext_obb_rw),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats),3009(readproc),3011(uhid),3012(readtracefs) context=u:r:shell:s0",
+                "ip_neigh": "10.13.102.21 dev wlan0 lladdr c8:7f:54:01:94:7c STALE\n10.13.102.64 dev wlan0 lladdr b8:be:f4:c2:bf:14 STALE\n10.13.102.5 dev wlan0 lladdr 90:09:d0:1a:83:e4 STALE\n10.13.102.1 dev wlan0 lladdr 78:9a:18:54:b8:f9 STALE\n10.13.102.79 dev wlan0 lladdr 02:11:32:25:63:bb STALE\nfe80::babe:f4ff:febc:cacf dev wlan0 lladdr b8:be:f4:bc:ca:cf STALE\nfe80::7a9a:18ff:fe54:b8f9 dev wlan0 lladdr 78:9a:18:54:b8:f9 router STALE\nfe80::babe:f4ff:fec2:bf14 dev wlan0 lladdr b8:be:f4:c2:bf:14 STALE\nfe80::babe:f4ff:febc:caf9 dev wlan0 lladdr b8:be:f4:bc:ca:f9 STALE",
+                "ip6_route": "fe80::/64 dev wlan0 table 1000000015 proto static metric 1024 pref medium\nfe80::/64 dev dummy0 table 1002 proto kernel metric 256 pref medium\ndefault dev dummy0 table 1002 proto static metric 1024 pref medium\nfe80::/64 dev wlan0 table 1015 proto kernel metric 256 pref medium\nfe80::/64 dev wlan0 table 1015 proto static metric 1024 pref medium\ndefault via fe80::7a9a:18ff:fe54:b8f9 dev wlan0 table 1015 proto ra metric 1024 expires 1622sec pref medium\nlocal ::1 dev lo table local proto kernel metric 0 pref medium\nlocal fe80::416:b9ff:feac:5b65 dev wlan0 table local proto kernel metric 0 pref medium\nlocal fe80::1450:43ff:feec:93c4 dev dummy0 table local proto kernel metric 0 pref medium\nmulticast ff00::/8 dev dummy0 table local proto kernel metric 256 pref medium\nmulticast ff00::/8 dev wlan0 table local proto kernel metric 256 pref medium",
+                "ip_addr": "1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000\n    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00\n    inet 127.0.0.1/8 scope host lo\n       valid_lft forever preferred_lft forever\n    inet6 ::1/128 scope host \n       valid_lft forever preferred_lft forever\n2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000\n    link/ether 16:50:43:ec:93:c4 brd ff:ff:ff:ff:ff:ff\n    inet6 fe80::1450:43ff:feec:93c4/64 scope link \n       valid_lft forever preferred_lft forever\n3: ifb0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 32\n    link/ether f6:d4:d4:9b:51:9c brd ff:ff:ff:ff:ff:ff\n4: ifb1: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 32\n    link/ether fe:16:ea:60:a2:d1 brd ff:ff:ff:ff:ff:ff\n5: tunl0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN group default qlen 1000\n    link/ipip 0.0.0.0 brd 0.0.0.0\n6: gre0@NONE: <NOARP> mtu 1476 qdisc noop state DOWN group default qlen 1000\n    link/gre 0.0.0.0 brd 0.0.0.0\n7: gretap0@NONE: <BROADCAST,MULTICAST> mtu 1462 qdisc noop state DOWN group default qlen 1000\n    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:f",
+                "ip_monitor": "EXEC_TIMEOUT(newProcess)",
+                "dhcp_log": "Recently active IpClient logs:\nIpClient.wlan0\n  IpClient.wlan0 APF dump:\n    No active ApfFilter; IpClient not yet started.\n  \n  IpClient.wlan0 current ProvisioningConfiguration:\n    N/A\n  \n  IpClient.wlan0 StateMachine dump:\n    2026-07-30T14:15:44.904384 - CMD_UPDATE_L2INFORMATION wlan0/15 0 0 Layer2InformationParcelable{l2Key: null, cluster: null, bssid: null} [rcvd_in=null, proc_in=null]\n    2026-07-30T14:15:45.903681 - CMD_UPDATE_L2INFORMATION wlan0/15 0 0 Layer2InformationParcelable{l2Key: We37ae5a065df5f7e, cluster: G8ead16cc1945078e, bssid: 24:5a:4c:5f:6d:2e} [rcvd_in=null, proc_in=null]\n    2026-07-30T14:15:45.917119 - CMD_STOP wlan0/15 1 0 null [rcvd_in=StoppedState, proc_in=IpClient$StoppedState]\n    2026-07-30T14:15:45.917386 - CMD_UPDATE_HTTP_PROXY wlan0/15 0 0 null [rcvd_in=StoppedState, proc_in=IpClient$StoppedState]\n    2026-07-30T14:15:45.921937 - CMD_UPDATE_TCP_BUFFER_SIZES wlan0/15 0 0 1730560,3461120,6922240,524288,1048576,4525824 [rcvd_in=StoppedState, proc_in=IpClient$StoppedState]\n    2026-07-30T14:15:45.922243 - INVOKE getInterfaceVersion\n    2026-07-30T14:15:45.923124 - CMD_START wlan0/15 0 0 ProvisioningConfiguration{mUniqueEui64AddressesOnly: false, mEnab",
+                "wifi_dump": "rec[2]: time=07-30 15:44:09.909 processed=L2ConnectedState org=L3ConnectedState dest=<null> what=CMD_POST_DHCP_ACTION screen=off v4 v4r v4dns v6r\n rec[3]: time=07-30 15:44:09.915 processed=L2ConnectedState org=L3ConnectedState dest=<null> what=CMD_IPV4_PROVISIONING_SUCCESS screen=off DhcpResultsParcelable{baseConfiguration: IP address 10.13.102.125/24 Gateway 10.13.102.1  DNS servers: [ 10.13.102.1 ] Domains hudelist.local, leaseDuration: 600, mtu: 0, serverAddress: 10.13.102.1, vendorInfo: null, serverHostName: , captivePortalApiUrl: null}\n rec[4]: time=07-30 15:44:09.916 processed=ConnectableState org=L3ConnectedState dest=<null> what=CMD_UPDATE_LINKPROPERTIES screen=off 3 0 v4 v4r v4dns v6r\n rec[5]: time=07-30 15:48:27.650 processed=ConnectableState org=L3ConnectedState dest=<null> what=CMD_INSTALL_PACKET_FILTER screen=off len=435\n--\n rec[13]: time=07-30 15:49:09.976 processed=L2ConnectedState org=L3ConnectedState dest=<null> what=CMD_POST_DHCP_ACTION screen=on v4 v4r v4dns v6r\n rec[14]: time=07-30 15:49:10.006 processed=L2ConnectedState org=L3ConnectedState dest=<null> what=CMD_IPV4_PROVISIONING_SUCCESS screen=on DhcpResultsParcelable{baseConfiguration: IP address 10.13.102.125"
+            },
+            "durationMs": 55313
+        }
+    ]
+}
@@ -7,6 +7,44 @@ schedule), UDP data plane (ECHO with observation block, TIMESYNC, HMAC gate, ant
 anti-amplification — wire format covered by tests). Not yet: TCP/TLS echo, STUN, canary DNS,
 actions, observations API, admin UI beyond token minting.

+## Deployment requirements
+
+**No reverse proxy, no 80/443 — by design.** Traefik/nginx on the same host are fine; this
+server never touches their ports, and putting it *behind* them would break two protocol
+properties:
+
+- Clients trust the control plane **only** via the SPKI pin from enrollment (self-signed is
+  first-class). A proxy terminates TLS with its own rotating ACME cert → pins break. The pin
+  model exists so no real certificate is ever needed.
+- On the data plane, **the observed source address/port/TTL/DSCP *is* the measurement**. Any
+  proxy or NAT layer (including Docker's) substitutes its own — hence host networking.
+
+What a target host actually needs:
+
+| Port | Proto | Purpose | Notes |
+|---|---|---|---|
+| 8443 | tcp | control plane (pinned HTTPS) | any port — it travels in the enrollment QR + profile |
+| 8442 | udp | UDP probe data plane | any port, profile-driven |
+| 8441 | tcp | TCP/TLS echo | any port (not yet implemented) |
+| 3478 | udp | STUN | keep standard: vanilla RFC 5389 for tool interop; rarely contended |
+| 8444 | tcp | admin | loopback-only by design — reach via SSH tunnel |
+
+All configurable via `ECHOLOT_*_LISTEN`. Plus:
+
+1. **A public IP on the host** (v4, ideally also v6 — v6 topology issues are half of what
+   clients want to measure). Behind NAT, plain port-forwards work.
+2. **Second IP (optional):** full RFC 5780 NAT-behavior discovery (`stun-5780`) needs an
+   alternate reply address; without it the profile advertises `stun-basic` and clients degrade
+   gracefully.
+3. **Delegated DNS subzone (optional, later):** the `canary-dns` capability needs port 53 on
+   some IP + an NS delegation (mind systemd-resolved on 127.0.0.53). Absent → capability simply
+   not advertised.
+4. **Outbound freedom** for connect-back / delayed-echo actions — no extra inbound ports;
+   generated traffic goes only to the session's observed source.
+
+Deliberately out of scope here: an echo listener on 443 (to detect port-based egress filtering)
+— that genuinely needs 443 and belongs on a dedicated IP, not on a host running a reverse proxy.
+
 ## Run in Docker (config via env)

 ```sh
@@ -27,7 +65,22 @@ sudo /usr/local/bin/echolot-server --uninstall-systemd
 ```

 Config precedence: flags > `ECHOLOT_*` env > defaults. Every flag has an env twin
-(`--udp-listen` ↔ `ECHOLOT_UDP_LISTEN`).
+(`--udp-listen` ↔ `ECHOLOT_UDP_LISTEN`). Host config lives in `/etc/echolot-server.env`
+(seeded by `--install-systemd`, never overwritten).
+
+**Multi-IP hosts:** listen specs are comma-separated, and you should bind explicit addresses —
+a wildcard bind would also claim management-only IPs:
+
+```sh
+ECHOLOT_CONTROL_LISTEN=203.0.113.10:8443,[2001:db8::10]:8443
+ECHOLOT_UDP_LISTEN=203.0.113.10:8442,203.0.113.11:8442,[2001:db8::10]:8442,[2001:db8::11]:8442
+```
+
+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).

 ### Self-update (opt-in, native only)

@@ -38,7 +38,9 @@ import (
 	"echo-lot.app/server/internal/selfupdate"
 	"echo-lot.app/server/internal/session"
 	"echo-lot.app/server/internal/store"
+	"echo-lot.app/server/internal/stun"
 	"echo-lot.app/server/internal/system"
+	"echo-lot.app/server/internal/tcpecho"
 )

 // Version is stamped via -ldflags "-X main.Version=v1.2.3" in CI.
@@ -63,8 +65,10 @@ func run() error {
 		fmt.Println(Version)
 		return nil
 	case actions.InstallSystemd:
-		// The unit runs this same binary in serve mode with env-based config.
-		return system.InstallSystemd(nil)
+		// The unit runs this same binary in serve mode; host config comes
+		// from /etc/echolot-server.env. A self-update timer is installed
+		// only when an update API is configured.
+		return system.InstallSystemd(cfg.SelfUpdateAPI)
 	case actions.UninstallSystemd:
 		return system.UninstallSystemd()
 	case actions.SelfUpdate:
@@ -93,22 +97,44 @@ func serve(cfg *config.Config) error {
 	slog.Info("control-plane certificate", "pin-sha256", pin)

 	sessions := session.NewManager(15 * time.Minute)
+	dp := &dataplane.Server{Sessions: sessions}
+	tcpSrv := &tcpecho.Server{}
+
+	caps := []string{"udp-probe", "delayed-echo", "connect-back"}
+	if len(config.Addrs(cfg.TCPListen)) > 0 {
+		caps = append(caps, "tcp-echo")
+	}
+
 	ctl := &control.Server{
 		Store: st, Sessions: sessions, Name: cfg.Name,
-		UDPPort: mustPort(cfg.UDPListen), TCPPort: mustPort(cfg.TCPListen), PinB64: pin,
+		UDPPort: mustPort(firstAddr(cfg.UDPListen)), TCPPort: mustPort(firstAddr(cfg.TCPListen)),
+		StunPort: mustPort(firstAddr(cfg.StunListen)), PinB64: pin,
+		DelayedEcho: dp.SendDelayedEcho,
+		TCPRecent:   func(ip string) any { return tcpSrv.RecentFor(ip) },
 	}

 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer stop()
-	errCh := make(chan error, 4)
+	ctlAddrs := config.Addrs(cfg.ControlListen)
+	udpAddrs := config.Addrs(cfg.UDPListen)
+	errCh := make(chan error, len(ctlAddrs)+len(udpAddrs)+2)

-	// Control plane (HTTPS, pin-based trust)
+	// Control plane (HTTPS, pin-based trust) — one shared server, one
+	// listener per configured address; Shutdown closes them all.
 	ctlSrv := &http.Server{
-		Addr: cfg.ControlListen, Handler: ctl.Handler(),
+		Handler:           ctl.Handler(),
 		TLSConfig:         &tls.Config{Certificates: []tls.Certificate{cert}, MinVersion: tls.VersionTLS12},
 		ReadHeaderTimeout: 10 * time.Second,
 	}
-	go func() { errCh <- fmt.Errorf("control: %w", ctlSrv.ListenAndServeTLS("", "")) }()
+	for _, addr := range ctlAddrs {
+		ln, err := net.Listen("tcp", addr)
+		if err != nil {
+			return fmt.Errorf("control listen %s: %w", addr, err)
+		}
+		go func(a string, l net.Listener) {
+			errCh <- fmt.Errorf("control %s: %w", a, ctlSrv.ServeTLS(l, "", ""))
+		}(addr, ln)
+	}

 	// Admin/health (plain HTTP, localhost by default; spec §7)
 	admin := http.NewServeMux()
@@ -129,20 +155,59 @@ func serve(cfg *config.Config) error {
 	adminSrv := &http.Server{Addr: cfg.AdminListen, Handler: admin, ReadHeaderTimeout: 10 * time.Second}
 	go func() { errCh <- fmt.Errorf("admin: %w", adminSrv.ListenAndServe()) }()

-	// UDP data plane
-	udpAddr, err := net.ResolveUDPAddr("udp", cfg.UDPListen)
+	// UDP data plane — one socket per configured address. Distinct sockets
+	// (not wildcard) also guarantee responses leave from the address the
+	// request arrived on, which stun-5780 will rely on.
+	var udpConns []*net.UDPConn
+	for _, addr := range udpAddrs {
+		udpAddr, err := net.ResolveUDPAddr("udp", addr)
 		if err != nil {
-		return err
+			return fmt.Errorf("udp addr %s: %w", addr, err)
 		}
-	udpConn, err := net.ListenUDP("udp", udpAddr)
+		conn, err := net.ListenUDP("udp", udpAddr)
 		if err != nil {
-		return fmt.Errorf("udp listen: %w", err)
+			return fmt.Errorf("udp listen %s: %w", addr, err)
+		}
+		udpConns = append(udpConns, conn)
+		go func(a string, c *net.UDPConn) {
+			errCh <- fmt.Errorf("udp %s: %w", a, dp.Serve(c))
+		}(addr, conn)
+	}
+
+	// TCP echo (spec §4)
+	var tcpLns []net.Listener
+	for _, addr := range config.Addrs(cfg.TCPListen) {
+		ln, err := net.Listen("tcp", addr)
+		if err != nil {
+			return fmt.Errorf("tcp listen %s: %w", addr, err)
+		}
+		tcpLns = append(tcpLns, ln)
+		go func(a string, l net.Listener) {
+			errCh <- fmt.Errorf("tcp %s: %w", a, tcpSrv.Serve(l))
+		}(addr, ln)
+	}
+
+	// STUN (spec §4) — advertises stun-5780 only with ≥2 same-family addrs.
+	var stunSrv *stun.Server
+	if stunAddrs := config.Addrs(cfg.StunListen); len(stunAddrs) > 0 {
+		stunSrv, err = stun.Listen(stunAddrs)
+		if err != nil {
+			return fmt.Errorf("stun listen: %w", err)
+		}
+		go func() { errCh <- fmt.Errorf("stun: %w", stunSrv.Serve()) }()
+		if stunSrv.Has5780() {
+			ctl.Capabilities = append(caps, "stun-5780")
+		} else {
+			ctl.Capabilities = append(caps, "stun-basic")
+		}
+	} else {
+		ctl.Capabilities = caps
 	}
-	dp := &dataplane.Server{Sessions: sessions}
-	go func() { errCh <- fmt.Errorf("udp: %w", dp.Serve(udpConn)) }()

 	slog.Info("listening",
-		"control", cfg.ControlListen, "admin", cfg.AdminListen, "udp", cfg.UDPListen)
+		"control", ctlAddrs, "admin", cfg.AdminListen, "udp", udpAddrs,
+		"tcp", config.Addrs(cfg.TCPListen), "stun", config.Addrs(cfg.StunListen),
+		"capabilities", ctl.Capabilities)

 	select {
 	case <-ctx.Done():
@@ -151,13 +216,28 @@ func serve(cfg *config.Config) error {
 		defer cancel()
 		_ = ctlSrv.Shutdown(shutCtx)
 		_ = adminSrv.Shutdown(shutCtx)
-		_ = udpConn.Close()
+		for _, c := range udpConns {
+			_ = c.Close()
+		}
+		for _, l := range tcpLns {
+			_ = l.Close()
+		}
+		if stunSrv != nil {
+			stunSrv.Close()
+		}
 		return nil
 	case err := <-errCh:
 		return err
 	}
 }

+func firstAddr(spec string) string {
+	if a := config.Addrs(spec); len(a) > 0 {
+		return a[0]
+	}
+	return ""
+}
+
 func mustPort(listen string) int {
 	_, p, err := net.SplitHostPort(listen)
 	if err != nil {
@@ -26,6 +26,7 @@ type Config struct {
 	// Data plane
 	UDPListen  string // ECHOLOT_UDP_LISTEN / --udp-listen (spec default port 8442)
 	TCPListen  string // ECHOLOT_TCP_LISTEN / --tcp-listen (spec default port 8441)
+	StunListen string // ECHOLOT_STUN_LISTEN / --stun-listen (spec default 3478; empty disables)

 	// Admin UI / health listener (spec §7: localhost-only by default)
 	AdminListen string // ECHOLOT_ADMIN_LISTEN / --admin-listen
@@ -60,11 +61,12 @@ func Load(args []string) (*Config, *Actions, error) {
 	c := &Config{}
 	a := &Actions{}

-	fs.StringVar(&c.ControlListen, "control-listen", envOr("CONTROL_LISTEN", ":8443"), "control-plane HTTPS listen address")
+	fs.StringVar(&c.ControlListen, "control-listen", envOr("CONTROL_LISTEN", ":8443"), "control-plane HTTPS listen address(es), comma-separated")
 	fs.StringVar(&c.TLSCert, "tls-cert", envOr("TLS_CERT", ""), "TLS cert path (empty: self-signed in state dir)")
 	fs.StringVar(&c.TLSKey, "tls-key", envOr("TLS_KEY", ""), "TLS key path (empty: self-signed in state dir)")
-	fs.StringVar(&c.UDPListen, "udp-listen", envOr("UDP_LISTEN", ":8442"), "UDP data-plane listen address")
-	fs.StringVar(&c.TCPListen, "tcp-listen", envOr("TCP_LISTEN", ":8441"), "TCP echo listen address")
+	fs.StringVar(&c.UDPListen, "udp-listen", envOr("UDP_LISTEN", ":8442"), "UDP data-plane listen address(es), comma-separated")
+	fs.StringVar(&c.TCPListen, "tcp-listen", envOr("TCP_LISTEN", ":8441"), "TCP echo listen address(es), comma-separated")
+	fs.StringVar(&c.StunListen, "stun-listen", envOr("STUN_LISTEN", ":3478"), "STUN listen address(es), comma-separated; empty disables (spec §4)")
 	fs.StringVar(&c.AdminListen, "admin-listen", envOr("ADMIN_LISTEN", "127.0.0.1:8444"), "admin/health listen address (keep localhost)")
 	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")
@@ -88,6 +90,20 @@ func Load(args []string) (*Config, *Actions, error) {
 	return c, a, nil
 }

+// 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
+// SSH-only management IP).
+func Addrs(spec string) []string {
+	var out []string
+	for _, a := range strings.Split(spec, ",") {
+		if a = strings.TrimSpace(a); a != "" {
+			out = append(out, a)
+		}
+	}
+	return out
+}
+
 // Actions are one-shot verbs that exit instead of serving.
 type Actions struct {
 	InstallSystemd   bool
@@ -7,14 +7,19 @@
 package control

 import (
+	"crypto/rand"
 	"crypto/sha256"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/base64"
+	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"log/slog"
+	"net"
 	"net/http"
 	"net/netip"
+	"strconv"
 	"strings"
 	"time"

@@ -29,12 +34,19 @@ type Server struct {
 	Store    *store.Store
 	Sessions *session.Manager
 	Name     string
-	// Targets/capabilities for the profile response. The skeleton offers only
+	// Targets/capabilities for the profile response. The server offers only
 	// what it actually implements; the registry grows with the code.
 	UDPPort  int
 	TCPPort  int
+	StunPort int
 	// SPKI pin of the serving cert, for the profile's pins[] field.
 	PinB64 string
+	// Capabilities as computed at startup from what is actually wired up.
+	Capabilities []string
+	// TCPRecent returns recent TCP-echo connections for a source IP (may be nil).
+	TCPRecent func(ip string) any
+	// DelayedEcho schedules/sends a DELAYED_ECHO for a session (may be nil).
+	DelayedEcho func(sess *session.Session, actionID string) error
 }

 func (s *Server) Handler() http.Handler {
@@ -43,11 +55,131 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("GET /v1/profile", s.profile)
 	mux.HandleFunc("POST /v1/sessions", s.newSession)
 	mux.HandleFunc("DELETE /v1/sessions/{id}", s.deleteSession)
-	// TODO(spec §5, §6): /v1/sessions/{id}/actions, /v1/sessions/{id}/observations
-	// TODO(spec §4): POST /v1/echo, GET /v1/tls-reference
+	mux.HandleFunc("GET /v1/sessions/{id}/observations", s.observations)
+	mux.HandleFunc("POST /v1/sessions/{id}/actions", s.actions)
+	// TODO(spec §4): POST /v1/echo, GET /v1/tls-reference; TLS-echo/JA4
+	// TODO(spec §5): downtrain, big_send, frag_send, throughput
 	return mux
 }

+// 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))
+	if dev == nil {
+		writeJSON(w, http.StatusUnauthorized, map[string]string{"error": "unknown credential"})
+		return nil
+	}
+	sess := s.Sessions.ByID(r.PathValue("id"))
+	if sess == nil || sess.Device != dev.ID {
+		writeJSON(w, http.StatusNotFound, map[string]string{"error": "no such session"})
+		return nil
+	}
+	return sess
+}
+
+// observations is spec §6 — everything the server witnessed for a session.
+func (s *Server) observations(w http.ResponseWriter, r *http.Request) {
+	sess := s.sessionAuth(w, r)
+	if sess == nil {
+		return
+	}
+	packetsSeen, udp, cb := sess.Observations()
+	var tcp any
+	if s.TCPRecent != nil {
+		// Correlate by source IP: TCP echo carries no session id on the wire.
+		if ds := sess.DataSource(); ds.IsValid() {
+			tcp = s.TCPRecent(ds.Addr().Unmap().String())
+		} else if sess.ControlSource.IsValid() {
+			tcp = s.TCPRecent(sess.ControlSource.Unmap().String())
+		}
+	}
+	writeJSON(w, http.StatusOK, map[string]any{
+		"udp":          map[string]any{"packets_seen": packetsSeen, "packets": udp},
+		"tcp":          tcp,
+		"connect_back": cb,
+		// TODO(spec §6): http echo records, dns_canary
+	})
+}
+
+// actions is spec §5 — authenticated asymmetric operations. Implemented:
+// delayed_echo, connect_back. Destination is ALWAYS the session's observed
+// source (data-plane source; connect_back uses the control-plane source).
+func (s *Server) actions(w http.ResponseWriter, r *http.Request) {
+	sess := s.sessionAuth(w, r)
+	if sess == nil {
+		return
+	}
+	var req struct {
+		Action   string `json:"action"`
+		DelayS   int    `json:"delay_s"`
+		Protocol string `json:"protocol"`
+		Port     int    `json:"port"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "bad body"})
+		return
+	}
+	actionID := randomID()
+	switch req.Action {
+	case "delayed_echo":
+		if s.DelayedEcho == nil {
+			writeJSON(w, http.StatusNotImplemented, map[string]string{"error": "delayed_echo not wired"})
+			return
+		}
+		delay := min(max(req.DelayS, 1), 600)
+		if !sess.DataSource().IsValid() {
+			writeJSON(w, http.StatusConflict, map[string]string{"error": "no data-plane traffic seen yet — send an ECHO first"})
+			return
+		}
+		time.AfterFunc(time.Duration(delay)*time.Second, func() {
+			if err := s.DelayedEcho(sess, actionID); err != nil {
+				slog.Debug("delayed echo failed", "err", err)
+			}
+		})
+		writeJSON(w, http.StatusAccepted, map[string]any{"action_id": actionID, "delay_s": delay})
+	case "connect_back":
+		if req.Port < 1 || req.Port > 65535 || (req.Protocol != "tcp" && req.Protocol != "udp") {
+			writeJSON(w, http.StatusBadRequest, map[string]string{"error": "connect_back needs protocol tcp|udp and a port"})
+			return
+		}
+		target := net.JoinHostPort(sess.ControlSource.Unmap().String(), strconv.Itoa(req.Port))
+		go func() {
+			start := time.Now()
+			conn, err := net.DialTimeout(req.Protocol, target, 5*time.Second)
+			res := session.ConnectBackResult{ActionID: actionID, RttMs: float64(time.Since(start).Microseconds()) / 1000}
+			switch {
+			case err == nil:
+				res.Result = "connected"
+				if req.Protocol == "udp" {
+					// UDP "dial" always succeeds locally; send one datagram
+					// so the client actually observes something.
+					_, _ = conn.Write([]byte("echolot-connect-back " + actionID))
+				}
+				conn.Close()
+			case isTimeout(err):
+				res.Result = "timeout"
+			default:
+				res.Result = "refused"
+			}
+			sess.RecordConnectBack(res)
+		}()
+		writeJSON(w, http.StatusAccepted, map[string]any{"action_id": actionID, "target": target})
+	default:
+		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "unknown or unimplemented action"})
+	}
+}
+
+func isTimeout(err error) bool {
+	var ne net.Error
+	return errors.As(err, &ne) && ne.Timeout()
+}
+
+func randomID() string {
+	var b [8]byte
+	_, _ = rand.Read(b[:])
+	return hex.EncodeToString(b[:])
+}
+
 func bearer(r *http.Request) string {
 	h := r.Header.Get("Authorization")
 	if v, ok := strings.CutPrefix(h, "Bearer "); ok {
@@ -103,12 +235,13 @@ func (s *Server) profile(w http.ResponseWriter, r *http.Request) {
 		// source_url makes GPL §6 compliance mechanical for operators of
 		// modified builds and gives clients provenance for the measurement.
 		"source_url":   "", // TODO: stamp from build metadata
-		"capabilities": []string{"udp-probe"},
+		"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,
 		}},
 		"pins":      []string{"pin-sha256:" + s.PinB64},
 		"next_pins": []string{},
@@ -11,9 +11,11 @@ import (
 	"crypto/hmac"
 	"crypto/sha256"
 	"encoding/binary"
+	"fmt"
 	"log/slog"
 	"net"
 	"net/netip"
+	"sync"
 	"time"

 	"echo-lot.app/server/internal/session"
@@ -27,6 +29,7 @@ const (
 	TypeEchoResp    = 0x02
 	TypeTimesyncReq = 0x07
 	TypeTimesyncRsp = 0x08
+	TypeDelayedEcho = 0x0B
 )

 type Server struct {
@@ -34,13 +37,22 @@ type Server struct {
 	// Epoch for server-side t_rx/t_tx: process start; observation consumers
 	// only need differences plus the timesync exchange, not absolute time.
 	start time.Time
+
+	mu    sync.Mutex
+	conns []*net.UDPConn
 }

+// Serve runs the read loop for one socket; call once per bound address.
+// The socket is retained so actions (delayed echo) can pick a family-matching
+// sender later.
 func (s *Server) Serve(conn *net.UDPConn) error {
+	s.mu.Lock()
+	if s.start.IsZero() {
 		s.start = time.Now()
+	}
+	s.conns = append(s.conns, conn)
+	s.mu.Unlock()
 	buf := make([]byte, 65535)
-	oob := make([]byte, 0)
-	_ = oob // TODO: recvmsg w/ IP_RECVTOS+IP_RECVTTL via golang.org/x/net for TTL/DSCP/ECN observation
 	for {
 		n, raddr, err := conn.ReadFromUDPAddrPort(buf)
 		if err != nil {
@@ -51,6 +63,36 @@ func (s *Server) Serve(conn *net.UDPConn) error {
 	}
 }

+// connFor picks a retained socket whose family matches the target.
+func (s *Server) connFor(target netip.AddrPort) *net.UDPConn {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	want4 := target.Addr().Unmap().Is4()
+	for _, c := range s.conns {
+		la := c.LocalAddr().(*net.UDPAddr).AddrPort()
+		if la.Addr().Unmap().Is4() == want4 {
+			return c
+		}
+	}
+	return nil
+}
+
+// SendDelayedEcho fires one DELAYED_ECHO packet at the session's observed
+// data-plane source (spec §5: the NAT-mapping-lifetime primitive). The
+// payload carries the action id for correlation.
+func (s *Server) SendDelayedEcho(sess *session.Session, actionID string) error {
+	target := sess.DataSource()
+	if !target.IsValid() {
+		return fmt.Errorf("session has no observed data-plane source yet")
+	}
+	conn := s.connFor(target)
+	if conn == nil {
+		return fmt.Errorf("no data-plane socket matches target family")
+	}
+	s.send(conn, target, sess, TypeDelayedEcho, 0, []byte(actionID))
+	return nil
+}
+
 // handle enforces spec §3.1/§3.4: unknown prefix, bad HMAC, expired session,
 // replayed seq → silent drop, never a response.
 func (s *Server) handle(conn *net.UDPConn, raddr netip.AddrPort, pkt []byte, tRxNs int64) {
@@ -80,6 +122,10 @@ func (s *Server) handle(conn *net.UDPConn, raddr netip.AddrPort, pkt []byte, tRx
 		return
 	}
 	sess.NoteDataSource(raddr)
+	sess.RecordUDP(session.UDPObservation{
+		Seq: seq, TRxNs: tRxNs, TTxNs: time.Since(s.start).Nanoseconds(),
+		Src: raddr.String(), Size: len(pkt), Type: typ,
+	})

 	switch typ {
 	case TypeEchoReq:
@@ -8,6 +8,8 @@
 package selfupdate

 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -49,7 +51,11 @@ func Run(api, currentVersion string) error {
 	if err := json.NewDecoder(resp.Body).Decode(&rel); err != nil {
 		return err
 	}
-	if rel.TagName == "" || rel.TagName == currentVersion {
+	// Tags are namespaced (server-v1.2.3) but binaries are stamped with the
+	// bare version (v1.2.3) — compare the normalized forms or the updater
+	// would re-download the same version forever.
+	latest := strings.TrimPrefix(rel.TagName, "server-")
+	if rel.TagName == "" || latest == currentVersion {
 		fmt.Printf("already current (%s)\n", currentVersion)
 		return nil
 	}
@@ -65,6 +71,35 @@ func Run(api, currentVersion string) error {
 		return fmt.Errorf("release %s has no asset %q", rel.TagName, want)
 	}

+	// The release must carry SHA256SUMS; refuse to update without it. This
+	// protects download integrity (truncation, proxy mangling). It is NOT a
+	// defense against a compromised Gitea — both files come from the same
+	// place; a detached signature would be needed for that (still TODO).
+	var sums string
+	for _, a := range rel.Assets {
+		if a.Name == "SHA256SUMS" {
+			resp, err := client.Get(a.URL)
+			if err != nil {
+				return fmt.Errorf("fetching SHA256SUMS: %w", err)
+			}
+			b, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+			resp.Body.Close()
+			if err != nil {
+				return err
+			}
+			sums = string(b)
+		}
+	}
+	wantSum := ""
+	for _, line := range strings.Split(sums, "\n") {
+		if fields := strings.Fields(line); len(fields) == 2 && fields[1] == want {
+			wantSum = fields[0]
+		}
+	}
+	if wantSum == "" {
+		return fmt.Errorf("release %s has no SHA256SUMS entry for %q — refusing to update", rel.TagName, want)
+	}
+
 	self, err := os.Executable()
 	if err != nil {
 		return err
@@ -81,15 +116,18 @@ func Run(api, currentVersion string) error {
 		os.Remove(tmp)
 		return err
 	}
-	_, err = io.Copy(f, dl.Body)
+	h := sha256.New()
+	_, err = io.Copy(io.MultiWriter(f, h), dl.Body)
 	dl.Body.Close()
 	f.Close()
 	if err != nil {
 		os.Remove(tmp)
 		return err
 	}
-	// TODO(security): verify a detached signature/checksum asset before the
-	// rename — a Gitea compromise currently equals code execution here.
+	if got := hex.EncodeToString(h.Sum(nil)); got != wantSum {
+		os.Remove(tmp)
+		return fmt.Errorf("checksum mismatch for %s: got %s want %s", want, got, wantSum)
+	}
 	if err := os.Rename(tmp, self); err != nil {
 		os.Remove(tmp)
 		return fmt.Errorf("atomic replace failed (filesystem boundaries?): %w", err)
@@ -31,6 +31,64 @@ type Session struct {
 	// a bitmask of the 1024 preceding.
 	maxSeq uint32
 	window [16]uint64
+
+	// Observations (spec §6): per-packet UDP view + connect-back results.
+	packetsSeen uint64
+	udpObs      []UDPObservation // ring, newest last, cap obsCap
+	connectBack []ConnectBackResult
+}
+
+const obsCap = 4096
+
+// UDPObservation is the server's witnessed view of one data-plane packet.
+type UDPObservation struct {
+	Seq   uint32 `json:"seq"`
+	TRxNs int64  `json:"t_rx_ns"`
+	TTxNs int64  `json:"t_tx_ns"`
+	Src   string `json:"src"`
+	Size  int    `json:"size"`
+	Type  uint8  `json:"type"`
+}
+
+// ConnectBackResult records one connect-back action outcome.
+type ConnectBackResult struct {
+	ActionID string  `json:"action_id"`
+	Result   string  `json:"result"` // connected | refused | timeout
+	RttMs    float64 `json:"rtt_ms"`
+}
+
+// RecordUDP appends a packet observation (ring-capped).
+func (s *Session) RecordUDP(o UDPObservation) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.packetsSeen++
+	if len(s.udpObs) >= obsCap {
+		s.udpObs = s.udpObs[1:]
+	}
+	s.udpObs = append(s.udpObs, o)
+}
+
+// RecordConnectBack appends a connect-back outcome.
+func (s *Session) RecordConnectBack(r ConnectBackResult) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.connectBack = append(s.connectBack, r)
+}
+
+// Observations returns a copy of everything witnessed so far.
+func (s *Session) Observations() (packetsSeen uint64, udp []UDPObservation, cb []ConnectBackResult) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.packetsSeen, append([]UDPObservation(nil), s.udpObs...),
+		append([]ConnectBackResult(nil), s.connectBack...)
+}
+
+// DataSource returns the last verified data-plane source (invalid when the
+// session has not sent data-plane traffic yet).
+func (s *Session) DataSource() netip.AddrPort {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.dataSource
 }

 // KeySalt returns nothing — the salt is not retained after derivation; it is
@@ -87,6 +145,20 @@ func (m *Manager) ByWirePrefix(prefix [8]byte) *Session {
 	return s
 }

+// ByID resolves a full session id (sessions are keyed by their wire prefix).
+func (m *Manager) ByID(id string) *Session {
+	if len(id) < 16 {
+		return nil
+	}
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	s := m.byPrefix[id[:16]]
+	if s == nil || s.ID != id || time.Now().After(s.Expires) {
+		return nil
+	}
+	return s
+}
+
 func (m *Manager) Delete(id string) {
 	m.mu.Lock()
 	defer m.mu.Unlock()
@@ -0,0 +1,266 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Package stun implements an unmodified RFC 5389 STUN binding responder with
+// the RFC 5780 NAT-behavior-discovery attributes (OTHER-ADDRESS,
+// RESPONSE-ORIGIN, CHANGE-REQUEST) when alternate addresses are available.
+// No custom framing — interop with existing STUN tooling is a feature
+// (spec §4). Each configured primary address gets two sockets: the given
+// port and port+1 (the RFC 5780 alternate-port convention).
+package stun
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"log/slog"
+	"net"
+	"net/netip"
+)
+
+const (
+	magicCookie = 0x2112A442
+
+	typeBindingRequest = 0x0001
+	typeBindingSuccess = 0x0101
+
+	attrChangeRequest  = 0x0003
+	attrXorMapped      = 0x0020
+	attrSoftware       = 0x8022
+	attrResponseOrigin = 0x802B
+	attrOtherAddress   = 0x802C
+
+	changeIP   = 0x04
+	changePort = 0x02
+)
+
+// sock is one bound socket, addressable by (address index, port index).
+type sock struct {
+	conn *net.UDPConn
+	addr netip.AddrPort
+}
+
+// Server holds the socket grid: addrs × {primary, alternate} ports.
+type Server struct {
+	// socks[i][0] = primary port, socks[i][1] = alt port for address i.
+	socks [][2]*sock
+}
+
+// Listen binds primary+alternate sockets for every address. Addresses are
+// "ip:port" specs; the alternate port is port+1.
+func Listen(addrs []string) (*Server, error) {
+	s := &Server{}
+	for _, spec := range addrs {
+		ap, err := netip.ParseAddrPort(spec)
+		if err != nil {
+			return nil, err
+		}
+		var pair [2]*sock
+		for i, port := range []uint16{ap.Port(), ap.Port() + 1} {
+			bind := netip.AddrPortFrom(ap.Addr(), port)
+			conn, err := net.ListenUDP("udp", net.UDPAddrFromAddrPort(bind))
+			if err != nil {
+				s.Close()
+				return nil, err
+			}
+			pair[i] = &sock{conn: conn, addr: bind}
+		}
+		s.socks = append(s.socks, pair)
+	}
+	return s, nil
+}
+
+func (s *Server) Close() {
+	for _, pair := range s.socks {
+		for _, sk := range pair {
+			if sk != nil {
+				sk.conn.Close()
+			}
+		}
+	}
+}
+
+// Has5780 reports whether any address family has ≥2 addresses — the
+// prerequisite for full NAT behavior discovery.
+func (s *Server) Has5780() bool {
+	var v4, v6 int
+	for _, pair := range s.socks {
+		if pair[0].addr.Addr().Is4() || pair[0].addr.Addr().Is4In6() {
+			v4++
+		} else {
+			v6++
+		}
+	}
+	return v4 >= 2 || v6 >= 2
+}
+
+// Serve starts one read loop per socket and blocks until the first error.
+func (s *Server) Serve() error {
+	errCh := make(chan error, len(s.socks)*2)
+	for ai := range s.socks {
+		for pi := range s.socks[ai] {
+			go func(ai, pi int) { errCh <- s.loop(ai, pi) }(ai, pi)
+		}
+	}
+	return <-errCh
+}
+
+func (s *Server) loop(ai, pi int) error {
+	sk := s.socks[ai][pi]
+	buf := make([]byte, 1500)
+	for {
+		n, raddr, err := sk.conn.ReadFromUDPAddrPort(buf)
+		if err != nil {
+			return err
+		}
+		s.handle(ai, pi, buf[:n], raddr)
+	}
+}
+
+// otherAddr finds the "diagonal" alternate for RFC 5780: different address
+// (same family), different port. Returns nil when there is none.
+func (s *Server) other(ai int, sameFamily bool, fam4 bool) int {
+	for i, pair := range s.socks {
+		if i == ai {
+			continue
+		}
+		is4 := pair[0].addr.Addr().Is4() || pair[0].addr.Addr().Is4In6()
+		if !sameFamily || is4 == fam4 {
+			return i
+		}
+	}
+	return -1
+}
+
+func (s *Server) handle(ai, pi int, pkt []byte, raddr netip.AddrPort) {
+	if len(pkt) < 20 || binary.BigEndian.Uint16(pkt[0:2]) != typeBindingRequest {
+		return
+	}
+	if binary.BigEndian.Uint32(pkt[4:8]) != magicCookie {
+		return
+	}
+	msgLen := int(binary.BigEndian.Uint16(pkt[2:4]))
+	if 20+msgLen > len(pkt) {
+		return
+	}
+	var txid [12]byte
+	copy(txid[:], pkt[8:20])
+
+	// Parse CHANGE-REQUEST if present (RFC 5780 §7.2).
+	var change byte
+	for off := 20; off+4 <= 20+msgLen; {
+		at := binary.BigEndian.Uint16(pkt[off : off+2])
+		al := int(binary.BigEndian.Uint16(pkt[off+2 : off+4]))
+		if off+4+al > len(pkt) {
+			break
+		}
+		if at == attrChangeRequest && al >= 4 {
+			change = pkt[off+7]
+		}
+		off += 4 + al + (4-al%4)%4 // attributes are 32-bit aligned
+	}
+
+	// Pick the responding socket per CHANGE-REQUEST.
+	fam4 := raddr.Addr().Is4() || raddr.Addr().Is4In6()
+	rai, rpi := ai, pi
+	if change&changeIP != 0 {
+		if o := s.other(ai, true, fam4); o >= 0 {
+			rai = o
+		} else {
+			return // cannot honor — RFC says error response; silence is safer for a probe target
+		}
+	}
+	if change&changePort != 0 {
+		rpi = 1 - pi
+	}
+	responder := s.socks[rai][rpi]
+
+	resp := buildResponse(txid, raddr, responder.addr, s.otherAddress(ai, fam4))
+	if _, err := responder.conn.WriteToUDPAddrPort(resp, raddr); err != nil {
+		slog.Debug("stun write failed", "to", raddr, "err", err)
+	}
+}
+
+// otherAddress computes the OTHER-ADDRESS attribute value (alt IP, alt port)
+// for the client's family, or an invalid AddrPort when unavailable.
+func (s *Server) otherAddress(ai int, fam4 bool) netip.AddrPort {
+	if o := s.other(ai, true, fam4); o >= 0 {
+		return s.socks[o][1].addr
+	}
+	return netip.AddrPort{}
+}
+
+func buildResponse(txid [12]byte, mapped, origin, other netip.AddrPort) []byte {
+	attrs := xorMappedAttr(attrXorMapped, mapped, txid)
+	attrs = append(attrs, addrAttr(attrResponseOrigin, origin)...)
+	if other.IsValid() {
+		attrs = append(attrs, addrAttr(attrOtherAddress, other)...)
+	}
+	sw := []byte("echolot")
+	attrs = append(attrs, attrHeader(attrSoftware, len(sw))...)
+	attrs = append(attrs, pad4(sw)...)
+
+	msg := make([]byte, 20, 20+len(attrs))
+	binary.BigEndian.PutUint16(msg[0:2], typeBindingSuccess)
+	binary.BigEndian.PutUint16(msg[2:4], uint16(len(attrs)))
+	binary.BigEndian.PutUint32(msg[4:8], magicCookie)
+	copy(msg[8:20], txid[:])
+	return append(msg, attrs...)
+}
+
+func attrHeader(typ uint16, valLen int) []byte {
+	h := make([]byte, 4)
+	binary.BigEndian.PutUint16(h[0:2], typ)
+	binary.BigEndian.PutUint16(h[2:4], uint16(valLen))
+	return h
+}
+
+func pad4(b []byte) []byte {
+	for len(b)%4 != 0 {
+		b = append(b, 0)
+	}
+	return b
+}
+
+// addrValue encodes the RFC 5389 address structure (family, port, address).
+func addrValue(ap netip.AddrPort) []byte {
+	addr := ap.Addr().Unmap()
+	if addr.Is4() {
+		v := make([]byte, 8)
+		v[1] = 0x01
+		binary.BigEndian.PutUint16(v[2:4], ap.Port())
+		a4 := addr.As4()
+		copy(v[4:], a4[:])
+		return v
+	}
+	v := make([]byte, 20)
+	v[1] = 0x02
+	binary.BigEndian.PutUint16(v[2:4], ap.Port())
+	a16 := addr.As16()
+	copy(v[4:], a16[:])
+	return v
+}
+
+func addrAttr(typ uint16, ap netip.AddrPort) []byte {
+	v := addrValue(ap)
+	return append(attrHeader(typ, len(v)), v...)
+}
+
+// xorMappedAttr encodes XOR-MAPPED-ADDRESS (RFC 5389 §15.2).
+func xorMappedAttr(typ uint16, ap netip.AddrPort, txid [12]byte) []byte {
+	v := addrValue(ap)
+	binary.BigEndian.PutUint16(v[2:4], ap.Port()^uint16(magicCookie>>16))
+	var key [16]byte
+	binary.BigEndian.PutUint32(key[0:4], magicCookie)
+	copy(key[4:], txid[:])
+	for i := 4; i < len(v); i++ {
+		v[i] ^= key[i-4]
+	}
+	return append(attrHeader(typ, len(v)), v...)
+}
+
+// NewTxID is exported for tests and client code.
+func NewTxID() [12]byte {
+	var t [12]byte
+	_, _ = rand.Read(t[:])
+	return t
+}
@@ -0,0 +1,137 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package stun
+
+import (
+	"encoding/binary"
+	"net"
+	"net/netip"
+	"testing"
+	"time"
+)
+
+// bindingRequest builds a minimal RFC 5389 binding request.
+func bindingRequest(txid [12]byte, change byte) []byte {
+	var attrs []byte
+	if change != 0 {
+		attrs = append(attrs, attrHeader(attrChangeRequest, 4)...)
+		attrs = append(attrs, 0, 0, 0, change)
+	}
+	msg := make([]byte, 20, 20+len(attrs))
+	binary.BigEndian.PutUint16(msg[0:2], typeBindingRequest)
+	binary.BigEndian.PutUint16(msg[2:4], uint16(len(attrs)))
+	binary.BigEndian.PutUint32(msg[4:8], magicCookie)
+	copy(msg[8:20], txid[:])
+	return append(msg, attrs...)
+}
+
+// parseXorMapped extracts XOR-MAPPED-ADDRESS from a binding success.
+func parseXorMapped(t *testing.T, resp []byte, txid [12]byte) netip.AddrPort {
+	t.Helper()
+	if binary.BigEndian.Uint16(resp[0:2]) != typeBindingSuccess {
+		t.Fatalf("type = %#x, want binding success", resp[0:2])
+	}
+	msgLen := int(binary.BigEndian.Uint16(resp[2:4]))
+	for off := 20; off+4 <= 20+msgLen; {
+		at := binary.BigEndian.Uint16(resp[off : off+2])
+		al := int(binary.BigEndian.Uint16(resp[off+2 : off+4]))
+		if at == attrXorMapped {
+			v := append([]byte(nil), resp[off+4:off+4+al]...)
+			port := binary.BigEndian.Uint16(v[2:4]) ^ uint16(magicCookie>>16)
+			var key [16]byte
+			binary.BigEndian.PutUint32(key[0:4], magicCookie)
+			copy(key[4:], txid[:])
+			for i := 4; i < len(v); i++ {
+				v[i] ^= key[i-4]
+			}
+			if v[1] == 0x01 {
+				return netip.AddrPortFrom(netip.AddrFrom4([4]byte(v[4:8])), port)
+			}
+			return netip.AddrPortFrom(netip.AddrFrom16([16]byte(v[4:20])), port)
+		}
+		off += 4 + al + (4-al%4)%4
+	}
+	t.Fatal("no XOR-MAPPED-ADDRESS in response")
+	return netip.AddrPort{}
+}
+
+func TestBindingAndChangePort(t *testing.T) {
+	// Two loopback "addresses" is not possible portably, so exercise one
+	// address (basic binding + change-port); the change-IP path needs the
+	// two-address grid of a real deployment.
+	srv, err := Listen([]string{"127.0.0.1:0"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	// port 0 twice would collide at 1; rebind explicitly on free ports
+	srv.Close()
+	base := freePort(t)
+	srv, err = Listen([]string{netip.AddrPortFrom(netip.MustParseAddr("127.0.0.1"), base).String()})
+	if err != nil {
+		t.Skipf("cannot bind %d/%d: %v", base, base+1, err)
+	}
+	defer srv.Close()
+	go srv.Serve()
+
+	client, err := net.DialUDP("udp", nil, srv.socks[0][0].conn.LocalAddr().(*net.UDPAddr))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer client.Close()
+	client.SetDeadline(time.Now().Add(2 * time.Second))
+
+	txid := NewTxID()
+	client.Write(bindingRequest(txid, 0))
+	buf := make([]byte, 1500)
+	n, err := client.Read(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	mapped := parseXorMapped(t, buf[:n], txid)
+	want := client.LocalAddr().(*net.UDPAddr).AddrPort()
+	if mapped.Port() != want.Port() {
+		t.Fatalf("mapped port %d, want %d", mapped.Port(), want.Port())
+	}
+
+	// CHANGE-REQUEST(port): response must come from the alternate port.
+	// Dial-connected sockets drop packets from other sources, so use an
+	// unconnected socket and inspect the reply's source.
+	uc, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer uc.Close()
+	uc.SetDeadline(time.Now().Add(2 * time.Second))
+	txid2 := NewTxID()
+	uc.WriteToUDPAddrPort(bindingRequest(txid2, changePort), srv.socks[0][0].addr)
+	n, from, err := uc.ReadFromUDPAddrPort(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if from.Port() != srv.socks[0][1].addr.Port() {
+		t.Fatalf("change-port reply came from %v, want alt port %d", from, srv.socks[0][1].addr.Port())
+	}
+	parseXorMapped(t, buf[:n], txid2)
+}
+
+func freePort(t *testing.T) uint16 {
+	t.Helper()
+	// Find two adjacent free ports for the primary/alternate pair.
+	for tries := 0; tries < 20; tries++ {
+		l, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1)})
+		if err != nil {
+			continue
+		}
+		p := l.LocalAddr().(*net.UDPAddr).Port
+		l.Close()
+		l2, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: p + 1})
+		if err != nil {
+			continue
+		}
+		l2.Close()
+		return uint16(p)
+	}
+	t.Skip("no adjacent free UDP ports found")
+	return 0
+}
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: GPL-3.0-or-later

 // Package system implements native-host lifecycle: systemd unit install /
-// uninstall. Linux-only by nature; on other OSes the commands fail with a
-// clear message rather than pretending.
+// uninstall, plus an optional self-update timer. Linux-only by nature; on
+// other OSes the commands fail with a clear message rather than pretending.
 package system

 import (
@@ -14,7 +14,12 @@ import (
 	"runtime"
 )

-const unitPath = "/etc/systemd/system/echolot-server.service"
+const (
+	unitPath        = "/etc/systemd/system/echolot-server.service"
+	updateUnitPath  = "/etc/systemd/system/echolot-server-update.service"
+	updateTimerPath = "/etc/systemd/system/echolot-server-update.timer"
+	envFilePath     = "/etc/echolot-server.env"
+)

 const unitTemplate = `[Unit]
 Description=Echolot probe server
@@ -29,6 +34,8 @@ Restart=on-failure
 RestartSec=5
 StateDirectory=echolot-server
 Environment=ECHOLOT_STATE_DIR=/var/lib/echolot-server
+# Host-specific config (listen addresses etc.) lives here, not in the unit:
+EnvironmentFile=-%s
 # Hardening — the server needs sockets and its state dir, nothing else.
 NoNewPrivileges=true
 ProtectSystem=strict
@@ -40,9 +47,43 @@ PrivateTmp=true
 WantedBy=multi-user.target
 `

-// InstallSystemd writes the unit for THIS binary (absolute path), reloads
-// systemd, and enables the service. Idempotent.
-func InstallSystemd(extraArgs []string) error {
+const updateUnitTemplate = `[Unit]
+Description=Echolot server self-update
+After=network-online.target
+
+[Service]
+Type=oneshot
+ExecStart=%s --self-update --self-update-api=%s
+# The updater only replaces the binary; the restart activates it.
+ExecStartPost=/usr/bin/systemctl try-restart echolot-server.service
+`
+
+const updateTimerTemplate = `[Unit]
+Description=Daily Echolot server self-update check
+
+[Timer]
+OnCalendar=daily
+RandomizedDelaySec=1h
+Persistent=true
+
+[Install]
+WantedBy=timers.target
+`
+
+const envFileTemplate = `# Echolot server host configuration (systemd EnvironmentFile).
+# Bind explicit addresses on multi-IP hosts — a wildcard would also claim
+# management-only addresses. Comma-separated lists are supported.
+#ECHOLOT_CONTROL_LISTEN=203.0.113.10:8443,[2001:db8::10]:8443
+#ECHOLOT_UDP_LISTEN=203.0.113.10:8442,[2001:db8::10]:8442
+#ECHOLOT_TCP_LISTEN=203.0.113.10:8441,[2001:db8::10]:8441
+#ECHOLOT_ADMIN_LISTEN=127.0.0.1:8444
+#ECHOLOT_NAME=my-server
+`
+
+// InstallSystemd writes the unit(s) for THIS binary (absolute path), reloads
+// systemd, and enables the service. When selfUpdateAPI is non-empty, a daily
+// self-update timer is installed alongside. Idempotent.
+func InstallSystemd(selfUpdateAPI string) error {
 	if runtime.GOOS != "linux" {
 		return fmt.Errorf("--install-systemd is Linux-only (this is %s)", runtime.GOOS)
 	}
@@ -54,22 +95,36 @@ func InstallSystemd(extraArgs []string) error {
 	if err != nil {
 		return err
 	}
-	execStart := self
-	for _, a := range extraArgs {
-		execStart += " " + a
-	}
-	if err := os.WriteFile(unitPath, []byte(fmt.Sprintf(unitTemplate, execStart)), 0o644); err != nil {
+	if err := os.WriteFile(unitPath, []byte(fmt.Sprintf(unitTemplate, self, envFilePath)), 0o644); err != nil {
 		return fmt.Errorf("writing %s (need root?): %w", unitPath, err)
 	}
-	for _, cmd := range [][]string{
+	// Seed the env file once; never overwrite an existing one.
+	if _, err := os.Stat(envFilePath); os.IsNotExist(err) {
+		_ = os.WriteFile(envFilePath, []byte(envFileTemplate), 0o644)
+	}
+	cmds := [][]string{
 		{"systemctl", "daemon-reload"},
 		{"systemctl", "enable", "--now", "echolot-server.service"},
-	} {
+	}
+	if selfUpdateAPI != "" {
+		if err := os.WriteFile(updateUnitPath,
+			[]byte(fmt.Sprintf(updateUnitTemplate, self, selfUpdateAPI)), 0o644); err != nil {
+			return err
+		}
+		if err := os.WriteFile(updateTimerPath, []byte(updateTimerTemplate), 0o644); err != nil {
+			return err
+		}
+		cmds = append(cmds, []string{"systemctl", "enable", "--now", "echolot-server-update.timer"})
+	}
+	for _, cmd := range cmds {
 		if out, err := exec.Command(cmd[0], cmd[1:]...).CombinedOutput(); err != nil {
 			return fmt.Errorf("%v: %s: %w", cmd, out, err)
 		}
 	}
-	fmt.Printf("installed + started echolot-server.service (ExecStart=%s)\n", execStart)
+	fmt.Printf("installed echolot-server.service (ExecStart=%s, config: %s)\n", self, envFilePath)
+	if selfUpdateAPI != "" {
+		fmt.Println("installed echolot-server-update.timer (daily, randomized)")
+	}
 	return nil
 }

@@ -78,11 +133,14 @@ func UninstallSystemd() error {
 		return fmt.Errorf("--uninstall-systemd is Linux-only (this is %s)", runtime.GOOS)
 	}
 	// Stop/disable first; ignore "not loaded" errors so uninstall is idempotent.
+	_ = exec.Command("systemctl", "disable", "--now", "echolot-server-update.timer").Run()
 	_ = exec.Command("systemctl", "disable", "--now", "echolot-server.service").Run()
-	if err := os.Remove(unitPath); err != nil && !os.IsNotExist(err) {
+	for _, p := range []string{unitPath, updateUnitPath, updateTimerPath} {
+		if err := os.Remove(p); err != nil && !os.IsNotExist(err) {
 			return err
 		}
+	}
 	_ = exec.Command("systemctl", "daemon-reload").Run()
-	fmt.Println("removed echolot-server.service (state dir left in place)")
+	fmt.Println("removed echolot-server units (state dir and env file left in place)")
 	return nil
 }
@@ -0,0 +1,91 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Package tcpecho implements the spec §4 TCP echo: after connect the server
+// sends one JSON line with what it observed (source address/port, negotiated
+// MSS and TCP options from TCP_INFO), then byte-echoes until FIN. This is the
+// evidence source for mtu.mss_observed.
+//
+// The TLS/ALPN "elt-echo" variant (ClientHello capture + JA4) is not
+// implemented yet.
+package tcpecho
+
+import (
+	"encoding/json"
+	"io"
+	"net"
+	"sync"
+	"time"
+)
+
+// ConnRecord is what the observations API reports per connection (spec §6).
+type ConnRecord struct {
+	ConnectedAt time.Time `json:"connected_at"`
+	Src         string    `json:"src"`
+	MSS         int       `json:"mss"`
+	Options     []string  `json:"options"`
+}
+
+type Server struct {
+	mu     sync.Mutex
+	recent []ConnRecord // ring, newest last
+}
+
+const recentCap = 1024
+
+func (s *Server) record(r ConnRecord) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if len(s.recent) >= recentCap {
+		s.recent = s.recent[1:]
+	}
+	s.recent = append(s.recent, r)
+}
+
+// RecentFor returns records whose source IP matches ip.
+func (s *Server) RecentFor(ip string) []ConnRecord {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	var out []ConnRecord
+	for _, r := range s.recent {
+		if h, _, err := net.SplitHostPort(r.Src); err == nil && h == ip {
+			out = append(out, r)
+		}
+	}
+	return out
+}
+
+func (s *Server) Serve(ln net.Listener) error {
+	for {
+		conn, err := ln.Accept()
+		if err != nil {
+			return err
+		}
+		go s.handle(conn)
+	}
+}
+
+func (s *Server) handle(conn net.Conn) {
+	defer conn.Close()
+	_ = conn.SetDeadline(time.Now().Add(5 * time.Minute))
+
+	info := tcpInfo(conn) // platform-specific; zero values off-Linux
+	rec := ConnRecord{
+		ConnectedAt: time.Now().UTC(),
+		Src:         conn.RemoteAddr().String(),
+		MSS:         info.MSS,
+		Options:     info.Options,
+	}
+	s.record(rec)
+
+	greeting, _ := json.Marshal(map[string]any{
+		"observed_src": rec.Src,
+		"mss":          rec.MSS,
+		"options":      rec.Options,
+	})
+	if _, err := conn.Write(append(greeting, '\n')); err != nil {
+		return
+	}
+	// Byte-echo until FIN; the client's data is its own to interpret.
+	_, _ = io.Copy(conn, conn)
+}
@@ -0,0 +1,69 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build linux
+
+package tcpecho
+
+import (
+	"encoding/binary"
+	"net"
+	"syscall"
+	"unsafe"
+)
+
+type connInfo struct {
+	MSS     int
+	Options []string
+}
+
+// tcpInfo reads TCP_INFO via getsockopt. Only the head of struct tcp_info is
+// needed: 8 header bytes (state..wscale flags) then u32 rto, ato, snd_mss,
+// rcv_mss — layout is part of the kernel ABI and stable.
+func tcpInfo(conn net.Conn) connInfo {
+	tc, ok := conn.(*net.TCPConn)
+	if !ok {
+		return connInfo{}
+	}
+	raw, err := tc.SyscallConn()
+	if err != nil {
+		return connInfo{}
+	}
+	var buf [104]byte
+	var got bool
+	_ = raw.Control(func(fd uintptr) {
+		l := uint32(len(buf))
+		_, _, errno := syscall.Syscall6(syscall.SYS_GETSOCKOPT, fd,
+			uintptr(syscall.SOL_TCP), uintptr(syscall.TCP_INFO),
+			uintptr(unsafe.Pointer(&buf[0])), uintptr(unsafe.Pointer(&l)), 0)
+		got = errno == 0 && l >= 24
+	})
+	if !got {
+		return connInfo{}
+	}
+	// tcpi_options bit flags (include/uapi/linux/tcp.h)
+	const (
+		optTimestamps = 1
+		optSACK       = 2
+		optWscale     = 4
+		optECN        = 8
+	)
+	var opts []string
+	ob := buf[5]
+	if ob&optTimestamps != 0 {
+		opts = append(opts, "timestamps")
+	}
+	if ob&optSACK != 0 {
+		opts = append(opts, "sack")
+	}
+	if ob&optWscale != 0 {
+		opts = append(opts, "wscale")
+	}
+	if ob&optECN != 0 {
+		opts = append(opts, "ecn")
+	}
+	return connInfo{
+		MSS:     int(binary.LittleEndian.Uint32(buf[16:20])), // tcpi_snd_mss
+		Options: opts,
+	}
+}
@@ -0,0 +1,17 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build !linux
+
+package tcpecho
+
+import "net"
+
+type connInfo struct {
+	MSS     int
+	Options []string
+}
+
+// tcpInfo: TCP_INFO is Linux-only; other platforms report zero values and
+// the greeting says mss:0 — honest absence rather than a guess.
+func tcpInfo(net.Conn) connInfo { return connInfo{} }
Author	SHA1	Message	Date
mrambossekandClaude Opus 5	7b676e666e	server: STUN, TCP echo, observations API, delayed-echo + connect-back actions server-test / test (push) Successful in 27s Details server-release / image (push) Successful in 14s Details server-release / release (push) Successful in 27s Details - stun: RFC 5389 binding responder + RFC 5780 attributes (OTHER-ADDRESS, RESPONSE-ORIGIN, CHANGE-REQUEST) on a primary/alt-port socket grid per address; advertises stun-5780 with >=2 same-family addrs, else stun-basic. Unmodified framing for tooling interop. Tested. - tcpecho: JSON greeting with observed src + TCP_INFO MSS/options (Linux getsockopt; zeroed elsewhere via build tags), then byte echo. - session: per-packet UDP observations + connect-back results, ByID lookup. - control: GET /v1/sessions/{id}/observations, POST .../actions (delayed_echo → DELAYED_ECHO at the observed data-plane source; connect_back → dial the control-plane source, record connected/refused/ timeout+rtt). Capabilities computed from what is actually wired. - config/main: comma-separated STUN listeners; all planes bind explicit addresses; graceful shutdown of the new listeners. Full flow smoke-tested; go test green (stun binding/change-port, dataplane wire format). Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>	2026-07-31 19:53:36 +02:00
mrambossekandClaude Opus 5	507a8bfc1f	build-status: production server v0.2.0 live on the fmr VM Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>	2026-07-31 19:42:56 +02:00
mrambossekandClaude Opus 5	43e1ba778a	server: multi-address listeners, env-file config, self-update timer + checksums server-test / test (push) Successful in 24s Details server-release / image (push) Successful in 5s Details server-release / release (push) Successful in 26s Details - Comma-separated ECHOLOT_{CONTROL,UDP,TCP}_LISTEN; one listener/socket per address. Explicit binds matter on multi-IP hosts (a wildcard would also claim the SSH-only management address) and per-address UDP sockets are the substrate stun-5780 needs. - systemd unit reads /etc/echolot-server.env (seeded once, never overwritten); --install-systemd with --self-update-api also installs a daily randomized update timer that try-restarts the service. - selfupdate: SHA256SUMS verification is now mandatory before the atomic replace (integrity, not authenticity — signing still TODO). Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>	2026-07-31 19:40:36 +02:00
Markus RambossekandClaude Opus 5	4de3064f71	reports: build-5 runs on both devices — new toolchain is behaviour-neutral TB330FU (A15/SDK35) and CPH2747 (A16/SDK36) both re-run on the AGP 9.2 / Gradle 9.6 / Kotlin 2.2.10 / JDK 25 / targetSdk 36 toolchain. Every probe on both devices keeps the verdict it had on the previous build (tablet vs build-4, phone vs build-3), so the upgrade changed no observed capability. Dual-path Shizuku executor now confirmed on the current toolchain on both: phone exec_path=UserService, tablet exec_path=newProcess fallback, both 7/7. Collection-loop gotchas recorded in build-status.md, found while driving the phone over USB: - icmp.ping6's verdict is topology-dependent, not build-dependent. A run with only 2 networks up reported UNSUPPORTED; with cellular present it is the expected "echo reply on cellular only". Always read it against link.snapshot's network_count from the same report. - The Shizuku permission dialog times out after 30 s and the probe logs "permission not granted" at ~30027 ms. Grant it before starting a run. - uiautomator dump can report a stale idle state right after a tap; the exported JSON's durationMs values are the ground truth for completion. CLAUDE.md's collection loop is updated — over USB the run is fully driveable via am start / input tap / run-as cat, no manual export needed. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>	2026-07-30 17:35:53 +02:00
Markus RambossekandClaude Opus 5	edcad3e539	prober: AGP 9.2 / Gradle 9.6 / Kotlin 2.2.10, targetSdk 36, build 5 Lifts the build off the JDK-21 ceiling — the old AGP 8.7.3 pin could not run on JDK 25. Two AGP-9 migration edits were required: - AGP 9 ships built-in Kotlin support, so applying org.jetbrains.kotlin.android alongside it fails with "extension with name kotlin already registered"; the alias is dropped (kotlin.compose / kotlin.serialization stay, they are separate compiler plugins). - kotlinOptions { jvmTarget } came from that plugin and no longer resolves; AGP derives jvmTarget from compileOptions instead. compileSdk/targetSdk 35 -> 36, since Android Studio ships API 36.1 by default and installing 35 was avoidable churn. versionCode 5 so the reports from this toolchain are attributable (build 4 was already archived from the old one). Also fixes a missing comma that left .claude/settings.json invalid JSON. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>	2026-07-30 17:34:54 +02:00
mrambossekandClaude Opus 5	cae3c00990	server: document deployment requirements — no proxy, no 80/443, and why server-test / test (push) Successful in 24s Details Ports table, host-IP/second-IP/canary-zone requirements, and the two protocol properties (SPKI pinning, observed-source fidelity) that a reverse proxy would break. Coexists with traefik by never touching its ports. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>	2026-07-30 16:54:52 +02:00
mrambossekandClaude Opus 5	b7658a6777	server: selfupdate must normalize namespaced tags; build-status: pipeline green server-test / test (push) Successful in 24s Details Release tags are server-v1.2.3 but binaries are stamped v1.2.3 — the raw comparison would re-download the current version on every check. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>	2026-07-30 16:38:08 +02:00