refactor: split container switch and commit steps

internal/backendupdate/container.go

@@ -517,25 +517,47 @@ func (u *Updater) switchAndCommitContainer(ctx context.Context, transactionID st
 		}
 		switch record.State {
 		case transaction.StateSwitching:
-			reportProgress(report, Progress{TransactionID: transactionID, State: record.State, Message: fmt.Sprintf("Switching host Nginx backend traffic to port %d", request.TargetPort)})
+			if err := u.switchContainerTraffic(ctx, transactionID, request, before, after, report); err != nil {
+				return err
+			}
+		case transaction.StateVerifying:
+			if err := u.markContainerDraining(ctx, transactionID, request); err != nil {
+				return err
+			}
+		case transaction.StateDraining:
+			return u.drainAndCommitContainer(ctx, transactionID, request, report)
+		case transaction.StateCommitted:
+			return nil
+		case transaction.StateRollingBack:
+			return u.rollbackContainer(ctx, transactionID, request, before, after, errors.New("resuming container backend rollback"))
+		default:
+			return fmt.Errorf("container backend commit cannot continue transaction %s in state %s", transactionID, record.State)
+		}
+	}
+}
+
+func (u *Updater) switchContainerTraffic(ctx context.Context, transactionID string, request persistedContainerRequest, before hostnginx.Snapshot, after hostnginx.Snapshot, report ProgressReporter) error {
+	reportProgress(report, Progress{TransactionID: transactionID, State: transaction.StateSwitching, Message: fmt.Sprintf("Switching host Nginx backend traffic to port %d", request.TargetPort)})
 	operation := &gatewayOperation{controller: u.gateway, before: before, after: after, receiptPath: request.GatewayReceiptPath}
 	if _, err := u.coordinator.ExecuteStep(ctx, transactionID, containerGatewaySwitchIntent(request), operation); err != nil {
 		return u.rollbackContainer(ctx, transactionID, request, before, after, err)
 	}
-			if _, err := u.store.Transition(ctx, transactionID, transaction.StateVerifying, "host Nginx now routes backend traffic to the healthy container slot"); err != nil {
+	_, err := u.store.Transition(ctx, transactionID, transaction.StateVerifying, "host Nginx now routes backend traffic to the healthy container slot")
 	return err
 }
-		case transaction.StateVerifying:
+
+func (u *Updater) markContainerDraining(ctx context.Context, transactionID string, request persistedContainerRequest) error {
 	message := "container backend switch verified"
 	if request.PreviousContainer != "" {
 		message += "; previous container draining"
 	}
-			if _, err := u.store.Transition(ctx, transactionID, transaction.StateDraining, message); err != nil {
+	_, err := u.store.Transition(ctx, transactionID, transaction.StateDraining, message)
 	return err
 }
-		case transaction.StateDraining:
+
+func (u *Updater) drainAndCommitContainer(ctx context.Context, transactionID string, request persistedContainerRequest, report ProgressReporter) error {
 	if request.PreviousContainer != "" {
-				reportProgress(report, Progress{TransactionID: transactionID, State: record.State, Message: fmt.Sprintf("Draining previous backend container for %s", u.drain)})
+		reportProgress(report, Progress{TransactionID: transactionID, State: transaction.StateDraining, Message: fmt.Sprintf("Draining previous backend container for %s", u.drain)})
 		if err := waitContext(ctx, u.drain); err != nil {
 			return err
 		}
@@ -554,24 +576,11 @@ func (u *Updater) switchAndCommitContainer(ctx context.Context, transactionID st
 	if target.ImageReference != request.ImmutableReference && target.ImageReference != request.ImageReference {
 		return fmt.Errorf("target backend container %s image reference does not match the transaction", request.TargetContainer)
 	}
-			_, err = u.store.CommitBackendContainerDeployment(ctx, transactionID, transaction.BackendContainerDeployment{
+	_, err = u.store.CommitBackendContainerDeployment(ctx, transactionID, transaction.BackendContainerDeployment{ActivePort: request.TargetPort, ContainerName: request.TargetContainer, ImageDigest: request.ImageDigest, ContainerID: target.ID}, "container backend update committed")
-				ActivePort:    request.TargetPort,
-				ContainerName: request.TargetContainer,
-				ImageDigest:   request.ImageDigest,
-				ContainerID:   target.ID,
-			}, "container backend update committed")
 	if err == nil {
 		reportProgress(report, Progress{TransactionID: transactionID, State: transaction.StateCommitted, Message: "Container backend update committed"})
 	}
 	return err
-		case transaction.StateCommitted:
-			return nil
-		case transaction.StateRollingBack:
-			return u.rollbackContainer(ctx, transactionID, request, before, after, errors.New("resuming container backend rollback"))
-		default:
-			return fmt.Errorf("container backend commit cannot continue transaction %s in state %s", transactionID, record.State)
-		}
-	}
 }
 
 // rollbackContainer 执行容器后端补偿：恢复 Nginx 上游、停止被补偿的目标容器，并