- Implement stream-keyed ACK buffering in StreamConsumer with periodic and capacity-triggered flushes
- Consolidate delivery outbox persistence to a single post-dispatch write, cutting PostgreSQL outbox writes by 50%
- Make retry key deletion and idempotency TTL extension non-blocking on message success
- Add host-unique consumer identifiers across distributed delivery, engine, and enricher workers
- Add unit tests verifying buffered stream ACK flushing behavior