feat(multiplayer): enforce proposal decline cooldowns

multiplayer-next.md

@@ -1463,6 +1463,12 @@ simultaneous connections, releasing capacity on disconnect; this complements
 the bounded per-player event queue and prevents connection fan-out from
 becoming an unbounded account-level resource cost.
 
+Proposal explicit-decline cooldowns are now durable: the declining player is
+requeued for recovery, but a subsequent queue create is rejected until the
+playlist-specific cooldown computed by `domain.CooldownUntil` expires. The
+operation is idempotent and does not affect the other participants' requeue;
+timeout-derived cooldown recording remains a follow-up slice.
+
 ### Current local completion index (2026-09-01)
 
 The following Phase 8 slices have local implementation and verification evidence in this document: 8.29 dynamic allocated launch flags and endpoint handling; 8.30 allocator claim/reconciliation including provider-outcome recovery fencing; 8.31 signed assignment/roster validation; 8.35 initial-connect no-show and casual bot policy; 8.36 controlled drain and shutdown acknowledgment; 8.39–8.43 client state, assignment, profile, recovery, and idempotent action retry; 8.44 structured observability and content-aware redaction; 8.45 bounded API metrics export plus optional Prometheus scrape/alert rules; 8.46 normal/race/vet/fuzz coverage; 8.47–8.48 offline/testkit/Compose coverage; 8.50 atomic stalled-allocation recovery notifications; 8.51 the 10,000-client API load boundary; 8.52 the opt-in per-replica plus shared PostgreSQL regional allocator quota; and 8.53 the fail-closed promotion validator. Their remaining acceptance text is infrastructure or production dependent where explicitly noted below the corresponding row.