Re-applied onto 3aee29089 after `hermes update` reset main to origin/main.
1. web_routers/sessions.py: _resolve_session_id() classifies malformed-DB
errors via the existing is_malformed_db_error() and raises 503 at all five
call sites. delete_session_endpoint was the worst — an unresolvable id
counted as idempotent success, so DELETE reported it had removed a session
that was still on disk.
2. gateway/lifecycle_ledger.py: check_state_db_integrity() runs PRAGMA
quick_check(1) on the unclean-exit path only (~2s on 500MB) and records the
verdict into gateway-exit-diag.log. The 2026-08-31 corruption sat undetected
for 3.5 days because nothing ever looked.
3. hermes_cli/gateway.py: `gateway run --replace` gave the outgoing gateway 5s
before SIGKILL; SessionDB.close() runs a PASSIVE WAL checkpoint that does
not finish in 5s on a WAL 4x past the autocheckpoint threshold, and a kill
mid-checkpoint tears b-tree pages. Grace raised to 30s via a testable
_await_gateway_exit() that also re-checks after the final sleep (a PID
exiting in the last interval must not be SIGKILLed — PID-reuse hazard).
NOT added: wal_checkpoint(TRUNCATE) at shutdown — removed upstream in #45383
because a TRUNCATE reset races the live writer and tears b-tree pages.
Adversarial review: Codex gpt-5.6-sol, 9.0/10 across three groups, no must-fix.
Nio Thomas
ba7743b076