Summary

• add a file lock for file-backed PGLite brains so only one local gbrain process can open the same brain at a time
• fail fast with a clear error when the brain is already in use instead of letting PGLite crash obscurely
• recover stale .gbrain.lock files and stale postmaster.pid files when the recorded pid is no longer alive
• add focused tests for concurrent file-backed access and stale lock recovery

Why

Local PGLite brains are single-user, but the CLI currently allows multiple commands to open the same file-backed brain concurrently. In practice this can leave the brain wedged after interrupted imports or overlapping commands, with errors like PGLite failed to initialize properly instead of an actionable message.

This keeps the local path honest: serialize access, recover obvious stale state, and tell the user what to do.

Test plan

• bun test test/pglite-engine.test.ts
• verified new tests:
  • rejects a second connection to the same file-backed brain
  • recovers from stale .gbrain.lock and stale postmaster.pid

Notes

• this is intentionally scoped to local file-backed PGLite only
• in-memory PGLite behavior is unchanged
• repo-wide TypeScript still has unrelated pre-existing errors outside this patch