Closes#3139
Three layered fixes for the scenario where CLI and gateway write to
state.db concurrently, causing create_session() to fail with
'database is locked' and permanently disabling session_search on the
gateway side.
1. Increase SQLite connection timeout: 10s -> 30s
hermes_state.py: longer window for the WAL writer to finish a batch
flush before the other process gives up entirely.
2. INSERT OR IGNORE in create_session
hermes_state.py: prevents IntegrityError on duplicate session IDs
(e.g. gateway restarts while CLI session is still alive).
3. Don't null out _session_db on create_session failure (main fix)
run_agent.py: a transient lock at agent startup must not permanently
disable session_search for the lifetime of that agent instance.
_session_db now stays alive so subsequent flushes and searches work
once the lock clears.
4. New ensure_session() helper + call it during flush
hermes_state.py: INSERT OR IGNORE for a minimal session row.
run_agent.py _flush_messages_to_session_db: calls ensure_session()
before appending messages, so the FK constraint is satisfied even
when create_session() failed at startup. No-op when the row exists.
6fbb5e52e0