feat: enforce durable queue resource limits and backpressure

internal/storage/mysql/schedule_tick.go

@@ -153,8 +153,15 @@ func (s *ScheduleStore) tickOne(ctx context.Context, ns, id, queue core.ID) (int
 			if err != nil {
 				return err
 			}
+			backpressured := false
 			for _, decision := range batch.Decisions {
 				if err := s.saveOccurrence(ctx, tx, v, version, decision, now); err != nil {
+					if errors.Is(err, fault.QueueFull) {
+						// 已提交本批较早的决定仍保留；满额的原触发点留待下次按冻结策略处理。
+						t := decision.ScheduledAt
+						next, backpressured = &t, true
+						break
+					}
 					return err
 				}
 				if decision.Kind == "SKIPPED" {
@@ -163,7 +170,9 @@ func (s *ScheduleStore) tickOne(ctx context.Context, ns, id, queue core.ID) (int
 					fired++
 				}
 			}
-			next = batch.Next
+			if !backpressured {
+				next = batch.Next
+			}
 			if next == nil && cursor < v.CurrentVersion {
 				cursor++
 				needsInitialization = true
@@ -205,6 +214,9 @@ func (s *ScheduleStore) saveOccurrence(ctx context.Context, tx *sql.Tx, v schedu
 		if in.QueueID != v.QueueID {
 			return errors.New("schedule template queue mismatch")
 		}
+		if err := reserveQueueTask(ctx, tx, v.NamespaceID, v.QueueID); err != nil {
+			return err
+		}
 		policy, err := json.Marshal(in.Retry)
 		if err != nil {
 			return err