Reviewer egilewski identified that the 5s lock timeout fell open:
quarantine_zeroed_state_db() logged 'proceeding without the cross-
process lock' and continued to re-check + rename state.db. A slow or
paused startup that still owns the lock can overlap this fallback and
the two processes can again act on the same live file.
Fix: fail closed — return None without moving the file when the lock
cannot be acquired within 5s. Log an error with recovery guidance
(restore from state-snapshots).
Test: test_quarantine_fails_closed_when_lock_held holds the cross-
process lock from a background thread, calls quarantine, and asserts
it returns None without moving the zeroed file.
Reviewer egilewski identified two recovery-loss paths:
Path A — quarantine race (hermes_state.py):
SessionDB checks state.db before quarantine_zeroed_state_db() without a
shared cross-process lock, and Path.rename() may replace an existing
destination. Two writable startups can therefore move the first
instance's newly created database over the .zeroed-*.bak, erase the
original damaged-file evidence, and replace the live database with
another empty one.
Fix: add a cross-process lock (msvcrt on Windows, fcntl on POSIX)
around quarantine_zeroed_state_db() with a 5s bounded timeout. Under
the lock: re-check is_zeroed_state_db (another process may have already
quarantined it and created a fresh DB), use a PID-suffixed unique
destination, and non-clobbering rename with counter fallback.
Path B — size-cap pruning gap (hermes_cli/backup.py):
_too_large() runs before failed-database tracking. With keep=1 and a
size cap, an oversized state.db is omitted while failed_dbs stays empty,
so automatic pruning deletes the older complete snapshot that may
contain the only recoverable database.
Fix: track oversized DB files in a new oversized_skipped list (both in
the directory walk and top-level file loop). The manifest now records
oversized_skipped. Pruning is suppressed when failed_dbs or
oversized_skipped is non-empty, preserving the older complete snapshot
as recovery source.
Tests:
- test_concurrent_quarantine_no_clobber: two threads racing on the
same zeroed state.db — verifies quarantine backup survives with
original bytes and live DB is valid.
- test_oversized_db_suppresses_pruning: keep=1 + oversized state.db
verifies the older complete snapshot is not pruned.
All 33 tests pass (3 zeroed_state_db + 25 TestQuickSnapshot + 5
quarantine_forensic_logging).
Hardening for the Windows zeroed-state.db class (#68474):
- Surface critical stdout when pre-update/quick snapshot cannot copy a
present *.db (was log-only; update still looked successful).
- Detect all-NUL SQLite header on SessionDB open, quarantine the bytes,
and open a fresh DB with recovery guidance to state-snapshots.
Does not claim storage-stack root cause.
