Webhook deliveries created a unique one-shot session (delivery_id baked into
the session key at gateway/platforms/webhook.py:668) but the adapter fired
handle_message via asyncio.create_task WITHOUT ever ending the session
(webhook.py:713, pre-fix). Nothing else closes it: the gateway caches/expires
the agent per session_key but never calls end_session for the webhook path,
and _end_session_on_close teardown doesn't run for these fire-and-forget tasks.
SessionDB.prune_sessions (hermes_state.py:4965) only deletes rows WHERE
ended_at IS NOT NULL. So every webhook session stayed with ended_at NULL ->
unprunable -> unbounded state.db growth. This was the primary driver of the
SQLite lock-contention gateway outage.
Fix: wrap the delivery in _run_delivery_and_close, which awaits
handle_message and then (in finally, so failures still reap) calls
_end_webhook_session -> SessionDB.end_session(session_id, 'webhook_complete').
This mirrors how cron closes its session with 'cron_complete'
(cron/scheduler.py:3065). end_session is first-reason-wins and no-ops on an
already-ended row, so it never clobbers a compression/agent_close reason.
Adds tests/gateway/test_webhook_session_close.py asserting the invariant
(a completed webhook session has ended_at set + is prunable), including the
error-path case, against a real SessionStore + SessionDB.
14882bab7e