`hermes sessions optimize` could corrupt state.db. Root cause is Hermes,
not the SQLite WAL-reset bug (#69784).
close() on ANY file descriptor for a SQLite database cancels every POSIX
advisory lock the process holds on that file, including a running VACUUM's
EXCLUSIVE lock (sqlite.org/howtocorrupt.html section 2.2). Hermes byte-probed
live databases in several hot paths: the zeroed-state.db detector runs on every
SessionDB construction (and the gateway builds those constantly), and kanban's
post-commit invariant check ran after every COMMIT. While VACUUM rewrote the
file, those probes dropped its lock and let other processes write into it.
A/B against the real code, only variable being the raw read:
SQLite 3.50.4, VACUUM + concurrent writers, DELETE mode
raw open/close during VACUUM 8 vacuums, 319 vacuum errors, 2/2 corrupt
no raw read (control) 229 vacuums, 0 vacuum errors, 0/2 corrupt
SQLite 3.53.1 (WAL-reset FIXED) reproduces identically: 2/2 corrupt.
After this change: 0/4 corrupt, 0 vacuum errors.
Because the upgraded runtime corrupts too, replacing the embedded SQLite does
not fix this class; and because DELETE is where it reproduces, #70055's
"force DELETE on vulnerable builds" mitigation steered users into the failing
mode. That gate is reverted here: vulnerable builds get WAL again and still
warn so operators can upgrade.
- add hermes_cli/sqlite_safe_read.py: read page_count via PRAGMA over the
existing connection instead of open()+seek(28); byte-level probes are
restricted to before any connection exists and refused once one is live,
with an explicit force= escape for offline artifacts (snapshots, archives)
- track live connections in SessionDB and kanban's connect so that guard is
enforced rather than merely documented
- kanban's torn-extend check now only applies under a rollback journal; in WAL
a committed page may still legitimately sit in the -wal file
- revert the force-DELETE WAL gate and update the tests that pinned it
Regression tests assert the behavioural contract (an external process stays
locked out across Hermes' inspection calls) and were verified to fail when the
old raw-open behaviour is restored.
Assert the version matrix, fresh-DB DELETE fallback, already-WAL left
alone (no checkpoint/DELETE), fixed-SQLite WAL path, and warn-only
doctor output for vulnerable builds (#69784).
