The expose tracker used sync.Map for in-memory TTL tracking of active expose sessions, which broke and lost all sessions on restart.
Replace with SQL-backed operations that reuse the existing meta_last_renewed_at column:
- Add store methods: RenewEphemeralService, GetExpiredEphemeralServices, CountEphemeralServicesByPeer, EphemeralServiceExists
- Move duplicate/limit checks inside a transaction with row-level locking (SELECT ... FOR UPDATE) to prevent concurrent bypass
- Reaper re-checks expiry under row lock to avoid deleting a just-renewed service and prevent duplicate event emission
- Add composite index on (source, source_peer) for efficient queries
- Batch-limit and column-select the reaper query to avoid DB/GC spikes
- Filter out malformed rows with empty source_peer
