1.广角/主摄切换按钮已上移：

2.新增 isSwitchingLens 状态、避免切换镜头    stop 按钮禁用，不会触发 stopRecording
倍距按钮禁用，避免连续切换
ViewModel 层也兜底：isSwitchingLens=true 时直接拒绝 stop
3.合并失败兜底提示

lib/features/recording/model/model_recording_session.dart

@@ -7,6 +7,7 @@ class RecordingSessionState {
     this.isTouchLocked = true,
     this.isPreviewReady = false,
     this.isStartingRecording = false,
+    this.isSwitchingLens = false,
     this.hasDndAccess = false,
     this.isBatteryOptimizedIgnored = true,
     this.notificationsGranted = true,
@@ -19,12 +20,14 @@ class RecordingSessionState {
     this.errorMessage,
     this.permissionWarning,
     this.fileSaveFailed = false,
+    this.segmentOutputPaths = const [],
   });
 
   final RecordingStatus status;
   final bool isTouchLocked;
   final bool isPreviewReady;
   final bool isStartingRecording;
+  final bool isSwitchingLens;
   final bool hasDndAccess;
   final bool isBatteryOptimizedIgnored;
   final bool notificationsGranted;
@@ -37,6 +40,7 @@ class RecordingSessionState {
   final String? errorMessage;
   final String? permissionWarning;
   final bool fileSaveFailed;
+  final List<String> segmentOutputPaths;
 
   bool get isRecording => status.isRecording;
 
@@ -53,6 +57,7 @@ class RecordingSessionState {
     bool? isTouchLocked,
     bool? isPreviewReady,
     bool? isStartingRecording,
+    bool? isSwitchingLens,
     bool? hasDndAccess,
     bool? isBatteryOptimizedIgnored,
     bool? notificationsGranted,
@@ -65,6 +70,7 @@ class RecordingSessionState {
     String? errorMessage,
     String? permissionWarning,
     bool? fileSaveFailed,
+    List<String>? segmentOutputPaths,
     bool clearPermissionWarning = false,
     bool clearLastSaved = false,
   }) {
@@ -73,6 +79,7 @@ class RecordingSessionState {
       isTouchLocked: isTouchLocked ?? this.isTouchLocked,
       isPreviewReady: isPreviewReady ?? this.isPreviewReady,
       isStartingRecording: isStartingRecording ?? this.isStartingRecording,
+      isSwitchingLens: isSwitchingLens ?? this.isSwitchingLens,
       hasDndAccess: hasDndAccess ?? this.hasDndAccess,
       isBatteryOptimizedIgnored:
           isBatteryOptimizedIgnored ?? this.isBatteryOptimizedIgnored,
@@ -90,6 +97,7 @@ class RecordingSessionState {
           ? null
           : (permissionWarning ?? this.permissionWarning),
       fileSaveFailed: fileSaveFailed ?? this.fileSaveFailed,
+      segmentOutputPaths: segmentOutputPaths ?? this.segmentOutputPaths,
     );
   }
 }