Replaces the 1.5s HTTP polling loop for clarify with a Server-Sent Events endpoint at /api/clarify/stream that pushes clarify events to the browser instantly. Mirrors the approval SSE pattern from v0.50.248 (#1350) including all the correctness lessons:
- Atomic subscribe + initial snapshot under clarify._lock
- _clarify_sse_notify called inside _lock for ordering guarantees (no notify-out-of-order race)
- Notify passes head=q[0].data (head-fidelity, not the just-appended entry)
- resolve_clarify also calls notify after pop so trailing clarifies surface immediately (no stuck-clarify bug)
- Empty-state notify with None,0 after pop-empty so frontend hides the card
- 30s keepalive comments, _CLIENT_DISCONNECT_ERRORS handling
- Bounded queue (maxsize=16) with silent drop on full
- Frontend: EventSource with automatic 3s HTTP polling fallback on onerror
Co-authored-by: fxd-jason <wujiachen7@gmail.com>
fxd-jason