优化录制页面的相机预览逻辑，增加预览未就绪时的错误提示，确保用户体验更流畅。

lib/features/recording/pages/page_record.dart

@@ -135,7 +135,13 @@ class _RecordingPageState extends ConsumerState<RecordingPage> {
     final result = await ref
         .read(recordingViewModelProvider.notifier)
         .ensureCameraAndMicrophonePermissions();
-    if (result.allGranted) return true;
+    if (result.allGranted) {
+      final ready = ref.read(recordingViewModelProvider).session.isPreviewReady;
+      if (ready) return true;
+      if (!mounted) return false;
+      AppToast.show('相机预览启动失败，请重试');
+      return false;
+    }
     if (!mounted) return false;
 
     await RecordDialog.showSingle(

lib/features/recording/view-model/view_model_recording.dart

@@ -280,6 +280,12 @@ class RecordingViewModel extends Notifier<RecordingModel> {
 
     _updateSession((s) => s.copyWith(isMicrophoneGranted: microphoneGranted));
 
+    if (cameraGranted && !state.session.isPreviewReady) {
+      _updateSession((s) => s.copyWith(errorMessage: null));
+      await _listenStatus();
+      await restorePreview();
+    }
+
     return RecordingRequiredPermissions(
       cameraGranted: cameraGranted,
       microphoneGranted: microphoneGranted,
@@ -293,9 +299,13 @@ class RecordingViewModel extends Notifier<RecordingModel> {
   /// 开始录制，可选开启勿扰模式。
   Future<void> startRecording({bool enableDoNotDisturb = true}) async {
     final session = state.session;
-    if (!session.isPreviewReady ||
-        session.isRecording ||
-        session.isStartingRecording) {
+    if (session.isRecording || session.isStartingRecording) {
+      return;
+    }
+    if (!session.isPreviewReady) {
+      _updateSession(
+        (s) => s.copyWith(errorMessage: '相机预览未就绪，请稍后重试'),
+      );
       return;
     }