When FTS5 index corruption prevents INSERT INTO messages, the gateway
accumulates messages in _pending_messages (memory-only). On shutdown,
.clear() discards the only surviving copy — permanent user data loss.
Changes:
- Add gateway/shutdown_flush.py with flush_pending_to_file() and
recover_pending_to_db() for two-phase data preservation.
- Patch gateway/run.py: flush runner._pending_messages before clear()
in _stop_impl_body, and recover on startup after runner.start().
- Patch gateway/platforms/base.py: flush adapter._pending_messages
before clear() in the adapter shutdown path.
Recovery behavior:
- Reads pending JSON files from ~/.hermes/pending_messages/
- Inserts messages into state.db directly
- Per-session isolation: one corrupt session doesn't block others
- Successful recovery deletes the flush file
- Failed recovery re-saves for next startup retry
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