The salvaged _sync_session_model_from_agent reached into
self._session_db._execute_write with a duplicate inline read-modify-write
and a comment claiming SessionDB had no metadata updater — but
update_session_meta already exists for exactly this. It also called the
AsyncSessionDB forwarder synchronously (via _execute_write), which returns
an un-awaited coroutine, so the write silently never ran.
Route through the synchronous SessionDB (self._session_db._db) — the same
pattern the surrounding run_sync closure already uses (it runs off the
event loop in the executor) — and use the existing update_session_meta /
get_session helpers instead of raw SQL.
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