Vitest's forks pool SIGTERMs a fork when a test times out, which skips
`beforeExit`/`exit` handlers and leaves `kb-db-test-*` dirs behind.
`holdWriteLock` child processes also kept WAL/SHM handles open, blocking
recursive removal on macOS. Both paths now run cleanup: SIGTERM/SIGINT/
SIGHUP handlers sweep tracked dirs and re-raise the signal, and active
lock-helper children are tracked and SIGKILLed during cleanup so the
parent dir can be removed.
These leaks tripped scripts/check-test-isolation.mjs during deterministic
merge verification, failing auto-merge with "Completion handoff limbo
recovery exhausted" (e.g. FN-5521, FN-5486).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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