Initial commit: capability prober + design docs

Monorepo root for Echolot. Contains the no-root capability prober
(Kotlin/Compose, app.echo_lot.prober) and the four design docs that act
as the contract for the production app and the Go server.

LICENSE is deliberately absent — still undecided, see docs/build-status.md.

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

CLAUDE.md

@@ -0,0 +1,66 @@
+# Echolot — context for Claude Code
+
+This repo is the **capability prober** for the Echolot project: an F/OSS Android app for detecting
+and debugging local network issues (target audience: network engineers). The prober validates the
+no-root feasibility matrix on real hardware before the production app is built.
+
+## Project facts
+
+- **Name:** Echolot. Domain echo-lot.app. URI scheme `echolot://`. Namespace `app.echo_lot.*`
+  (hyphen→underscore; appIds/packages can't contain hyphens). Prober appId: `app.echo_lot.prober`.
+- **Stack:** native Kotlin + Jetpack Compose. No Flutter (all value is in platform APIs;
+  Flutter would be a Dart skin over a full Kotlin app + F-Droid build friction).
+- **Tiers:** `app` (no root), `shizuku` (ADB-shell privileges via wireless pairing, shipped in v1),
+  `root` (future module). Every result records which tier produced it.
+- **License:** undecided (GPLv3 vs Apache-2.0). LICENSE is a TODO before going public.
+
+## Design docs (source of truth, in `docs/`)
+
+- `docs/feature-catalog-and-feasibility.md` — full feature list + no-root feasibility matrix.
+- `docs/measurement-schema.md` — the archived/exportable measurement JSON format (observation vs
+  finding separation, two-clock rule, columnar trains, anonymization types).
+- `docs/probe-protocol.md` — client↔server wire protocol (pinned-TLS control plane, binary UDP data
+  plane with anti-amplification HMAC, STUN, canary DNS reference records).
+- `docs/build-status.md` — running log of decisions, what is delivered, and the next steps.
+
+The three specs are draft-complete and user-reviewed; treat them as the contract. `build-status.md`
+is the mutable one — update it as work lands.
+
+Keep prober result IDs aligned with the measurement-schema test-type registry.
+
+## Layout
+
+Monorepo. The prober is one deliverable; the Go server and the production app land as siblings.
+
+```
+docs/                          design docs (above) — apply repo-wide, not just to the prober
+echolot-prober/                the capability prober (self-contained Gradle build)
+  app/src/main/java/app/echo_lot/prober/
+    MainActivity.kt            Compose host, runs probes sequentially
+    probe/                     Probe interface + all app-tier probes + OS ABI helper
+    shizuku/                   AIDL UserService + ShizukuRunner (shell command exec)
+    export/Report.kt           JSON report + share intent
+    ui/ProberScreen.kt         result cards colored by verdict
+```
+
+## Conventions
+
+- Every probe returns a `ProbeResult` — never throws to the caller (MainActivity wraps anyway).
+- Uncertain OS API paths (getsockoptInt, recvmsg, nat64Prefix) are reached via reflection/runCatching
+  and reported, not assumed — the prober's purpose is to discover what exists.
+- Hardcoded Linux sockopt ABI numbers live in `OsAbi.kt` with rationale; do not "fix" them to
+  OsConstants names that don't exist.
+
+## Build
+
+From `echolot-prober/`: `./gradlew :app:assembleDebug` (needs local Android SDK; set `sdk.dir` in
+`echolot-prober/local.properties`). The Gradle build is rooted there, not at the repo root.
+First build downloads AGP/Compose/Shizuku from Google Maven + Maven Central.
+
+## 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.
+3. Fold the confirmed capabilities + Shizuku dump-format samples back into the production
+   `core-probe` / `core-shizuku` modules.