Adds a per-machine singleton lock that engages in
ProjectEngineManager.createAndStart() before any engine subsystems
spin up. Two fn dashboard processes can no longer run engines for the
same project on the same host — previously they would share .fusion/
state and corrupt worktrees / task rows for in-process projects.
The guard combines two independent checks:
- A proper-lockfile file at <project>/.fusion/engine.lock with
stale-lock recovery (auto-released on process death).
- A loopback listener on a hashed per-project address — UDS on
POSIX, named pipe on Windows. Stale UDS files are probed and
unlinked before a retry bind.
Failures raise EngineAlreadyRunningError. Both guards are released
from stopAll() and pauseProject(); a release on engine.start()
failure lets retries re-acquire cleanly.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
