emrg: daemon all-path stop logging + stop-reason tracking

[argszero]

Summary

Host rant 2026-08-19T14:02:37: any reason / any path the daemon stops must leave a detailed log — when, why, who triggered, what was cleaned up — so "why did the daemon disappear" is always answerable from emrgd.log instead of guesswork.

Changes (all in emrg/server/daemon.py unless noted)

1. _stop_reason tracking — the daemon records why it is stopping on every path:
   • shutdown_msg (client shutdown message) — also logs the sender's source tag
   • cancel (asyncio CancelledError — Ctrl+C / parent kill)
   • sigint (KeyboardInterrupt handler in run_server)
   • bind_exit (fixed-port admission self-exit, EADDRINUSE)
   • crash (unhandled exception in serve() — now logged with full traceback via exc_info=True, previously depended on the top-level handler)
2. serve() no longer swallows CancelledError silently — logs daemon serve cancelled (asyncio.CancelledError) — cleanup started.
3. New _shutdown_all() — refactored teardown with per-step logging:
   • entry: daemon stopping (reason=…, handlers=N) — cleaning up
   • each step logged with success/failure: background loop cancellations, scheduler stop, LLM client close, port-file removal, pid-file removal
   • exit: daemon stopped (reason=…, uptime=…s, steps=…, all_ok=…)
4. Shutdown message source tagging — loopback peers are indistinguishable, so senders now tag the message: emrg server stop (CLI) and stop_all (GUI/installer) send "source"; missing source degrades to unknown (backward compatible).
5. KeyboardInterrupt — now logs shutdown signal received (SIGINT), cleanup started.

Tests

5 new unit tests in tests/test_daemon.py (pure mocks — mock scheduler/LLM/background tasks; no real daemon is stopped or restarted, per the highest principle). Cover: stop-reason echo in start/final log lines, per-step cleanup logging, failing-step handling (all_ok=False), and shutdown-message peer/source logging incl. legacy missing-source. Python suite: 979 collected, 978 passed + 1 skipped; import + CLI checks green. Agent.md test count synced 974 → 979.

[argszero]

✅ LGTM — cycle. CI test + test-windows PASS (run 32222270573); local suite 979 collected (978 passed + 1 skipped); stop-reason tracking covers all 5 stop paths (shutdown_msg/cancel/sigint/bind_exit/crash); pure-mock tests never stop/restart a real daemon.

[argszero]

✅ LGTM — cycle. Head unchanged (1baa40b), CI test + test-windows PASS, MERGEABLE/CLEAN; stop-reason + _shutdown_all logging verified in prior local run.

[argszero]

✅ LGTM — cycle. Third consecutive approval (cycles 908/909/910); head unchanged, CI test + test-windows PASS, MERGEABLE/CLEAN.