fix(queue): 隔离异步准入故障并持久化退避

将 X-Async 调度改为逐任务阻塞协议，区分全局容量、平台容量、用户组 FIFO、任务级异常和系统级故障，避免单个历史毒任务触发整批回滚。\n\n新增持久化退避、单任务 CAS 重选、幂等终态事务、固定标签指标和损坏快照自愈，并修复 Worker 从 preparing 直接进入 finalizing 时的自等待死锁。\n\n验证：API 全量测试、PostgreSQL 集成场景、race、go vet、govulncheck、pnpm lint/test/build、Compose 与发布脚本测试通过；pnpm audit 命中未改动的 Nx 工具链既有漏洞。

apps/api/internal/securityevents/metrics.go

@@ -80,6 +80,15 @@ type Metrics struct {
 	taskAdmissionCancelled      atomic.Uint64
 	taskAdmissionExpired        atomic.Uint64
 	taskAdmissionMigrated       atomic.Uint64
+	asyncAdmissionAdmitted      atomic.Uint64
+	asyncAdmissionGlobalWait    atomic.Uint64
+	asyncAdmissionPlatformWait  atomic.Uint64
+	asyncAdmissionGroupWait     atomic.Uint64
+	asyncAdmissionReselect      atomic.Uint64
+	asyncAdmissionDeferred      atomic.Uint64
+	asyncAdmissionTerminal      atomic.Uint64
+	asyncAdmissionTaskError     atomic.Uint64
+	asyncAdmissionSystemError   atomic.Uint64
 	candidateNormalRotation     atomic.Uint64
 	candidateFullAvoided        atomic.Uint64
 	candidateQuotaRaceRotated   atomic.Uint64
@@ -260,6 +269,29 @@ func (m *Metrics) ObserveTaskAdmission(event string) {
 	}
 }
 
+func (m *Metrics) ObserveAsyncAdmissionDispatch(outcome string) {
+	switch outcome {
+	case "admitted":
+		m.asyncAdmissionAdmitted.Add(1)
+	case "global_wait":
+		m.asyncAdmissionGlobalWait.Add(1)
+	case "platform_wait":
+		m.asyncAdmissionPlatformWait.Add(1)
+	case "group_wait":
+		m.asyncAdmissionGroupWait.Add(1)
+	case "reselect":
+		m.asyncAdmissionReselect.Add(1)
+	case "deferred":
+		m.asyncAdmissionDeferred.Add(1)
+	case "terminal":
+		m.asyncAdmissionTerminal.Add(1)
+	case "task_error":
+		m.asyncAdmissionTaskError.Add(1)
+	case "system_error":
+		m.asyncAdmissionSystemError.Add(1)
+	}
+}
+
 func (m *Metrics) ObserveCandidateRouting(reason string) {
 	switch reason {
 	case "normal_rotation":
@@ -568,7 +600,10 @@ func (m *Metrics) Handler(provider MetricsSnapshotProvider, issuer, audience str
 		plainGauge(w, "easyai_gateway_task_admission_queue_depth", "Current persistent non-text task admission queue depth.", int64(admission.QueueDepth))
 		plainGauge(w, "easyai_gateway_task_admission_waiting_sync", "Current synchronous admission waiters.", int64(admission.WaitingSync))
 		plainGauge(w, "easyai_gateway_task_admission_waiting_async", "Current asynchronous admission waiters.", int64(admission.WaitingAsync))
+		plainGauge(w, "easyai_gateway_task_admission_deferred_async", "Asynchronous admissions quarantined until a future dispatch attempt.", int64(admission.DeferredAsync))
+		plainGauge(w, "easyai_gateway_task_admission_pending_reselect", "Waiting asynchronous admissions marked for candidate reselection.", int64(admission.PendingReselect))
 		plainFloatGauge(w, "easyai_gateway_task_admission_oldest_wait_seconds", "Age of the oldest persistent admission waiter.", admission.OldestWaitSeconds)
+		plainFloatGauge(w, "easyai_gateway_task_admission_oldest_dispatchable_wait_seconds", "Age of the oldest asynchronous admission currently eligible for dispatch.", admission.OldestDispatchableWaitSeconds)
 		plainGauge(w, "easyai_gateway_task_admission_expired_waiter_backlog", "Expired synchronous waiter leases awaiting reclamation.", int64(admission.ExpiredWaiterBacklog))
 		plainGauge(w, "easyai_gateway_task_admission_expired_deadline_backlog", "Expired queue deadlines awaiting reclamation.", int64(admission.ExpiredDeadlineBacklog))
 		outcomeCounters(w, "easyai_gateway_task_admissions_total", "Task admission transitions by bounded outcome.", []outcomeValue{
@@ -579,6 +614,17 @@ func (m *Metrics) Handler(provider MetricsSnapshotProvider, issuer, audience str
 			{"expired", m.taskAdmissionExpired.Load()},
 			{"candidate_migrated", m.taskAdmissionMigrated.Load()},
 		})
+		outcomeCounters(w, "easyai_gateway_async_admission_dispatch_total", "Asynchronous admission dispatcher decisions by bounded outcome.", []outcomeValue{
+			{"admitted", m.asyncAdmissionAdmitted.Load()},
+			{"global_wait", m.asyncAdmissionGlobalWait.Load()},
+			{"platform_wait", m.asyncAdmissionPlatformWait.Load()},
+			{"group_wait", m.asyncAdmissionGroupWait.Load()},
+			{"reselect", m.asyncAdmissionReselect.Load()},
+			{"deferred", m.asyncAdmissionDeferred.Load()},
+			{"terminal", m.asyncAdmissionTerminal.Load()},
+			{"task_error", m.asyncAdmissionTaskError.Load()},
+			{"system_error", m.asyncAdmissionSystemError.Load()},
+		})
 		taskAdmissionWaitHistogram(w, m)
 	})
 }