fix: retain realtime work through draining

R-02: add an OPEN/DRAINING/CLOSED lifecycle orthogonal to freshness. Effect and
recovery authorities are now awaited under a deadline: on expiry the commit
capability is revoked and the work aborted, the caller gets a bounded
non-retryable IDLE_TIMEOUT, and the underlying task is retained rather than
dropped. A draining stream refuses new events and recovery, and close() returns
a Promise that succeeds only once every retained task actually settled,
reporting IDLE_TIMEOUT otherwise.

R-03: a handoff fail-close moves active, probe, quiescing and transition leases
into a retired-writer set before clearing their references, and close() waits on
current and retired writers together, so an abandoned non-cooperative writer can
no longer make teardown report a false success.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/architecture/decisions/VD-28-realtime-events-web-push-and-bounded-polling.md

@@ -11,6 +11,26 @@
   첫 제품 stream/Web Push를 선택할 때, 또는 backend replay/hosting/provider
   protocol이 바뀔 때
 
+
+## 스트림 lifecycle은 freshness와 직교한다 (R-02, R-03)
+
+`RealtimeStreamLifecycle = OPEN | DRAINING | CLOSED`는 freshness
+(`UNKNOWN/CURRENT/STALE/RESYNCING`)와 별개다.
+
+- effect/recovery deadline에 도달하면 commit capability를 즉시 영구 무효화하고
+  abort한다. caller에는 bounded `IDLE_TIMEOUT`(non-retryable, operation
+  `APPLY`/`RECOVER`)을 반환하되 **실제 task는 버리지 않고 retain**한다.
+- retain된 task가 하나라도 있으면 stream은 `DRAINING`이고 새 event/recovery
+  admission을 거절한다. 실제 settlement가 일어나야 `STALE`로 돌아가
+  authoritative recovery를 요구하거나, close 요청이면 `CLOSED`가 된다.
+- `close()`는 `Promise<RealtimeResult<void>>`다. 모든 retain task가 실제로
+  settle해야 success이고, drain bound를 넘기면 `IDLE_TIMEOUT/CLOSE`를 반환하며
+  stream은 계속 `DRAINING`이다. teardown success가 곧 quiescence다.
+- LIVE↔POLL overflow fail-close는 active/probe/quiescing/transition lease를
+  모두 abort한 뒤 **retired writer set**으로 옮기고 나서 reference를 지운다.
+  `close()`는 current와 retired를 dedupe해 함께 기다리므로, 버려진
+  non-cooperative writer가 아직 실행 중인데 close가 성공을 보고할 수 없다.
+
 ## 배경
 
 현재 optional recipe catalog는 realtime capability에