fix: use buildMtime for daemon stale detection, preserve port on restart

[piotrski]

Summary

Follow-up to #41 which introduced daemon auto-restart but had two bugs:

1. Port lost on restart — ensureDaemon() restarted the daemon with port = undefined (most CLI commands don't pass a port), silently switching to 8097. Now preserves the original info.port.

2. False restarts in CI — comparing daemon.js mtime against startedAt was fragile: when build and daemon start happened close together, filesystem timestamp precision could make them appear out of order.

New approach

The daemon now records daemon.js's mtime at startup as buildMtime in daemon.json. The CLI compares the file's current mtime against this stored value — if they differ, the file was rebuilt and the daemon restarts. No tolerance or clock comparison needed.

Changes

• DaemonInfo gains optional buildMtime field
• Daemon writes daemon.js mtime to daemon.json on startup
• ensureDaemon() compares current mtime vs stored buildMtime
• Port is preserved from info.port when restarting

E2E test

New daemon-auto-restart.test.ts uses the full CLI lifecycle (start/stop/get tree) to verify:

• Daemon restarts (new PID, same port) when buildMtime doesn't match
• Daemon stays alive when buildMtime matches

Test plan

• 68 unit tests pass
• 34 e2e tests pass (including new auto-restart tests)
• CI green

🤖 Generated with Claude Code

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