Detect a routing key whose session is already ended in state.db
(end_reason set) inside get_or_create_session and drop the stale entry
instead of silently routing the message into a closed session.
Previously the only runtime cleanup of sessions.json was the startup
_prune_stale_sessions_locked (#52808/#54138), which requires a restart.
A session ended while the gateway stays alive — any path that finalizes
the DB row without clearing sessions.json — left a live routing key
pointing at a closed session. get_or_create_session never consulted
end_reason, so it returned that stale entry and every subsequent message
was silently dropped (no log, no error, no response) until the next
restart. This is the live-gateway variant of #52804/FM9, which needed an
actual gateway crash.
The guard drops the stale entry and falls through to
_recover_session_from_db, which reopens agent_close-ended rows and
resumes the SAME session_id (transcript preserved); if the row ended for
a non-recoverable reason (e.g. /new) it correctly starts a fresh
session. A warning is logged so the event is visible (the field
incident reported zero log output).
Adds tests/gateway/test_session_store_runtime_stale_guard.py covering
the _is_session_ended_in_db helper and the end-to-end routing self-heal
(recover-vs-fresh, live-entry untouched, stale-wins-over-suspended,
force_new short-circuit).
Closes#54878.
Co-authored-by: David Gutowsky <david.gutowsky@gmail.com>
3a83b6bc5d