The bus is up: decision 4 accepted; orin-status publishes yukart/host/*

Also: std::process::Command breaks the cross-compile fallback (GLIBC_2.39).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

docs/ROADMAP.md

@@ -67,8 +67,10 @@ provides a cross-check for reverse-engineered ones.
 
 ## Phase 3 — Bus and contracts
 
-- [ ] Stand up the broker; confirm MQTT holds up at real CAN rates (decision 4
-      in [ARCHITECTURE.md](ARCHITECTURE.md) is still *proposed*)
+- [x] Stand up the broker, 2026-10-12: mosquitto 2.0.11 on the car Orin,
+      localhost only. First publisher `orin-status` (svc-core,
+      `yukart/host/*`); `svc-gw` subscribes and serves it to the tablet
+- [ ] Confirm MQTT holds up at real CAN rates (`yukart/can/raw`)
 - [ ] Freeze v1 of topic names and payload schemas
 - [ ] `telemetry-gw` — external client access, including the serial bridge