# 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:** code is **GPL-3.0-or-later** (`LICENSE`), the specs in `docs/` are **CC-BY-4.0**
  (`docs/LICENSE`). New source files get the two-line SPDX header the existing ones carry.
  The server, when it lands, is GPL too — not AGPL (see `docs/build-status.md` for the reasoning).

## 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.