Scaffold repo: docs layout, guidelines and initial plan

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013kj58Jugkic783b8ZrtTVZ

docs/GUIDELINES.md

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+---
+type: default
+---
+# Mock and fixture guidelines
+
+## 1. Fixtures publish the real contract
+- A fixture emits the **real topic with the real payload schema**. `yukart/gnss/fix`
+  from a replayed track must be indistinguishable, at the bus, from a real fix.  
+- A fixture that invents its own topic or shape is worse than no fixture: it defers
+  the integration work instead of removing it.
+
+## 2. Never stub our own services
+- Stub the **car** and the **hardware**. Never stub `svc-gw`, `svc-nav` or anything
+  else we wrote.  
+- A stub of our own service is a second implementation of our own contract, and it
+  will drift from the first. Run the real service against fake inputs instead —
+  none of our services touch hardware, so they all run on x86 unmodified.
+
+## 3. Prefer upstream tools, wrap rather than rewrite
+- `vcan`, `canplayer` and ICSim already solve the CAN problem. This repo holds the
+  scripts that drive them, not reimplementations of them.
+
+## 4. Recorded logs are data, not source
+- `candump` logs and GPX tracks are artifacts. Reference them, do not commit them.
+
+## 5. To be added