completeByDbId only cleaned up in-memory state, leaving sdk_sessions rows
with status='active' and completed_at=NULL indefinitely. Ghost sessions
accumulated and exhausted the agent pool, causing 60s timeout errors.
- Add SessionStore.markSessionCompleted() to set status/completed_at/completed_at_epoch
- Call it at the start of completeByDbId before in-memory cleanup
- Inject SessionStore into SessionCompletionHandler via constructor
- Add 4 tests covering status, timestamps, isolation, and non-existent IDs
Closes#1532
Co-Authored-By: Claude <noreply@anthropic.com>
Ousama Ben Younes