Define the envelope, topic namespace and OBD-II signal registry

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_013kj58Jugkic783b8ZrtTVZ
2026-09-05 12:54:14 +09:00
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+---
+type: plan
+status: active
+updated: 2026-09-05
+---
+# Initial plan
+
+## What is defined
+
+The envelope, the topic namespace, and the standard OBD-II signals — the ones
+whose names, units and ranges are fixed by the standard rather than by the car.
+
+## What is not
+
+**Z27AG-specific signals.** They do not exist until Phase 2 identifies them from
+observed traffic. They arrive as DBC entries plus registry rows with
+`source: "z27ag"`, one at a time as each is confirmed.
+
+**Composite payload shapes.** `gnss/fix`, `nav/guidance`, `nav/route` and
+`system/<service>` have their fields named in `topics.json` but no JSON Schema
+yet. They get one when a publisher exists to constrain.
+
+## Order
+
+1. Schema validation available to all three languages — the Rust services, the
+   Python fixtures and the Dart client must reject a malformed message
+   identically, or the contract is decorative.
+2. `gnss/fix` schema, driven by what `tool-mock` replays.
+3. Z27AG signals, as Phase 2 confirms them.
+
+## Consumers
+
+| Repo | Reads |
+|---|---|
+| `svc-core` | signals, envelope, DBC |
+| `svc-gw` | topics, envelope |
+| `svc-nav` | topics, envelope |
+| `app-flutter` | topics, envelope, signals (for display units) |
+| `tool-mock` | all of it — fixtures publish the real schema |