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

README.md

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+---
+type: reference
+---
+# Contracts
+
+Part of **Project Yukart**, making an old 2008 Mitsubishi Z27AG a bit smarter with modern technologies.  
+This file serves as the minimalist portal to other docs
+
+
+## What this repo is about
+
+The topic namespace, payload schemas and signal registry that every other repo
+depends on. Rust services, Python tooling and the Dart client all read the same
+definitions from here.
+
+| File | Holds |
+|---|---|
+| [`schema/topics.json`](schema/topics.json) | Topic namespace: payload kind, retention, rate, publisher |
+| [`schema/envelope.json`](schema/envelope.json) | JSON Schema for the decoded-signal envelope |
+| [`schema/signals.json`](schema/signals.json) | Signal registry — the single source for name, unit, type and range |
+
+The Z27AG DBC lands here too, once Phase 2 produces one.
+
+- For implementation practice guidelines, refer to the [guidelines](docs/GUIDELINES.md);  
+- For implementation plans and history, refer to [them](docs/impl/);