Get Extension Events

Poll for extension lifecycle events the current user has triggered.

Events are scoped to the authenticated user via a server-derived keyspace (user:{user_id}); there is no client-controllable keyspace, so an authenticated user cannot read another user's flow-migration or bundle-reload events. A client-supplied keyspace query parameter is rejected with 422 so the contract is explicit -- previously the value was silently dropped, which masked client bugs that assumed it had effect.

svc.since() uses blocking sqlite3; run in a thread pool so the asyncio event loop is not held while waiting on disk I/O.