Finish durable abnormal query termination and compaction handling

WIP branch: https://github.com/OpenCoven/coven-code/tree/wip/post-pr175-stream-query-hardening

Follow-up scope:
- substantive stall/cancel durability
- unmatched tool closure
- proactive/reactive/emergency compaction cancellation
- retry output without empty durable assistants
- TUI DurableMessage handling
- full gates/reviews