fix(player): 持久化竖滑播放画面层

lib/pages/player/widgets/player_video_surface.dart

@@ -25,6 +25,9 @@ class PlayerVideoSurface extends StatefulWidget {
     this.fallback = PlayerOpeningFallback.black,
     this.warmSlotReused = false,
     this.waitForPlaybackFrame = false,
+    this.debugSlot = 'default',
+    this.debugIndex,
+    this.showFallbackBackground = true,
   });
 
   final VideoPlayerController? controller;
@@ -49,6 +52,9 @@ class PlayerVideoSurface extends StatefulWidget {
 
   /// 自动播放中的新集等待 position 首次前进后再移交画面。
   final bool waitForPlaybackFrame;
+  final String debugSlot;
+  final int? debugIndex;
+  final bool showFallbackBackground;
   final String videoUrl;
   final bool theater;
 
@@ -79,8 +85,11 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
     final value = widget.controller?.value;
     _updatePlaybackFlags(value);
     _videoSize = value != null && value.isInitialized ? value.size : null;
+    _logSlot('init', value);
     if (_firstFrameConfirmed(value)) {
       _confirmFirstFrame(initial: true);
+    } else {
+      _logLayer('placeholder', value);
     }
   }
 
@@ -88,13 +97,19 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
   void didUpdateWidget(covariant PlayerVideoSurface oldWidget) {
     super.didUpdateWidget(oldWidget);
     if (oldWidget.controller != widget.controller) {
+      _logSlot('controller-change-before', oldWidget.controller?.value);
       _detachController(oldWidget.controller);
       _resetForControllerChange();
       _attachController(widget.controller);
       final value = widget.controller?.value;
       _updatePlaybackFlags(value);
       _videoSize = value != null && value.isInitialized ? value.size : null;
-      if (_firstFrameConfirmed(value)) _confirmFirstFrame(initial: true);
+      _logSlot('controller-change-after', value);
+      if (_firstFrameConfirmed(value)) {
+        _confirmFirstFrame(initial: true);
+      } else {
+        _logLayer('placeholder', value);
+      }
       return;
     }
     if (!_transitioning &&
@@ -119,6 +134,7 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
 
   @override
   void dispose() {
+    _logSlot('dispose', widget.controller?.value);
     _detachController(widget.controller);
     _crossFade
       ..removeStatusListener(_handleFadeStatus)
@@ -143,10 +159,11 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
     return Stack(
       fit: StackFit.expand,
       children: [
-        const ColoredBox(
-          key: Key('player-fallback-background'),
-          color: AppColors.mediaBlack,
-        ),
+        if (widget.showFallbackBackground)
+          const ColoredBox(
+            key: Key('player-fallback-background'),
+            color: AppColors.mediaBlack,
+          ),
         if (showPlaceholder)
           KeyedSubtree(
             key: const Key('player-single-placeholder'),
@@ -210,14 +227,16 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
     _confirmationScheduled = true;
     if (kDebugMode) {
       debugPrint(
-        '[player-layer] ts=${DateTime.now().microsecondsSinceEpoch} '
+        '[player-layer] ts=${DateTime.now().millisecondsSinceEpoch} '
+        'slot=${widget.debugSlot} index=${widget.debugIndex ?? '-'} '
         'phase=first-frame-scheduled',
       );
     }
     WidgetsBinding.instance.addPostFrameCallback((_) {
       if (kDebugMode) {
         debugPrint(
-          '[player-layer] ts=${DateTime.now().microsecondsSinceEpoch} '
+          '[player-layer] ts=${DateTime.now().millisecondsSinceEpoch} '
+          'slot=${widget.debugSlot} index=${widget.debugIndex ?? '-'} '
           'phase=first-frame-callback mounted=$mounted',
         );
       }
@@ -246,6 +265,7 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
   void _confirmFirstFrame({bool initial = false}) {
     if (_frameConfirmed || _videoSize == null) return;
     _frameConfirmed = true;
+    _logSlot('firstFrameRendered', widget.controller?.value);
     final canSkipPlaceholder =
         widget.warmFrameAvailable || _placeholderSnapshot == null;
     if (canSkipPlaceholder) {
@@ -303,6 +323,8 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
         ? 'video'
         : _fallbackLabel(widget.fallback);
     final signature =
+        'slot=${widget.debugSlot} '
+        'index=${widget.debugIndex ?? '-'} '
         'phase=$phase warm=${widget.warmFrameAvailable ? 1 : 0} '
         'reusedWarm=${widget.warmSlotReused ? 1 : 0} '
         'frame=${_frameConfirmed ? 1 : 0} '
@@ -312,14 +334,34 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
         'init=${value?.isInitialized == true ? 1 : 0} '
         'position=${value?.position.inMilliseconds ?? 0} '
         'playing=${value?.isPlaying == true ? 1 : 0} '
-        'buffering=${value?.isBuffering == true ? 1 : 0}';
+        'buffering=${value?.isBuffering == true ? 1 : 0} '
+        'placeholder=${_placeholderLabel()}';
     if (signature == _lastLayerState) return;
     _lastLayerState = signature;
     debugPrint(
-      '[player-layer] ts=${DateTime.now().microsecondsSinceEpoch} $signature',
+      '[player-layer] ts=${DateTime.now().millisecondsSinceEpoch} $signature',
     );
   }
 
+  void _logSlot(String phase, VideoPlayerValue? value) {
+    if (!kDebugMode) return;
+    debugPrint(
+      '[player-layer] ts=${DateTime.now().millisecondsSinceEpoch} '
+      'slot=${widget.debugSlot} index=${widget.debugIndex ?? '-'} '
+      'phase=$phase init=${value?.isInitialized == true ? 1 : 0}',
+    );
+  }
+
+  String _placeholderLabel() {
+    if (_placeholderSnapshot == null) return 'none';
+    return switch (widget.fallback) {
+      PlayerOpeningFallback.handoff => 'handoff',
+      PlayerOpeningFallback.poster => 'poster',
+      PlayerOpeningFallback.thumbnails => 'thumbnails',
+      PlayerOpeningFallback.black => 'none',
+    };
+  }
+
   String _fallbackLabel(PlayerOpeningFallback fallback) {
     if (_placeholderSnapshot == null) return 'black';
     return switch (fallback) {