fix(lock): a live writer keeps its lock regardless of age (#1959)

[danusha2345]

Addresses ask 6 of #1959.

Problem

FileLock treated any lock older than two minutes as stale "regardless of PID status", and a live holder never refreshes the lock file. A sync that runs past two minutes is joined by the next one, and the two write the same rows at once. The report in #1959 has one sync running 75 minutes while newer syncs deleted the rows it kept adding.

Fix

The age test is gone: a lock is stale only when its PID is dead or unparseable. A holder that crashes still frees the lock, because its PID is dead. codegraph unlock stays the manual escape hatch the error message already names.

Tests

security.test.ts: a lock file backdated three minutes, holding a live PID, is still refused. Full suite on this branch (Linux, Node 22, native kernel): all tests pass except the known extraction.test.ts pool-worker crash from #1779 (fixed by #1883), which is intermittent and also occurs on main; that file alone passes 655/655.

🤖 Generated with Claude Code

[colbymchenry]

Thanks @danusha2345! Your commits here were carried into #2043 (authorship preserved), with a few follow-up changes from review, and that is now merged. Closing this one in favour of it. It will be in the next release.