fix(player): 优化封面过渡与换集起播

lib/core/data/services/playback_session.dart

@@ -41,7 +41,6 @@ class PlaybackSession extends ChangeNotifier {
   final Future<void> Function()? waitForFrame;
   final PlaybackCoordinator _coordinator;
   final Set<_PlayerSlot> _live = {};
-  final Set<String> _pausedEpisodeIds = {};
   _PlayerSlot? _active;
   _PlayerSlot? _next;
   _PlayerSlot? _previous;
@@ -207,9 +206,9 @@ class PlaybackSession extends ChangeNotifier {
     int? previousIndex,
   }) async {
     if (_closed || index < 0 || index >= episodes.length) return;
-    // 新集默认起播；用户手动暂停过的同一集滑回时继续尊重暂停。
+    // 切换到不同剧集时恢复播放；仍停留在同一集时保留用户暂停。
     if (!_selected || index != _currentIndex) {
-      _userWantsPlay = !_pausedEpisodeIds.contains(episodes[index].id);
+      _userWantsPlay = true;
     }
     final request = ++_generation;
     _selected = true;

lib/core/data/services/playback_session_controls.dart

@@ -37,16 +37,8 @@ extension PlaybackSessionControls on PlaybackSession {
     _syncPlayback();
   }
 
-  /// 记录用户播放意图；手动暂停的剧集滑回时不再自动起播。
+  /// 记录用户播放意图；切换剧集时会在 [PlaybackSession.select] 中恢复播放。
   void setUserWantsPlay(bool value) {
-    if (episodes.isNotEmpty) {
-      final episodeId = episodes[_currentIndex].id;
-      if (value) {
-        _pausedEpisodeIds.remove(episodeId);
-      } else {
-        _pausedEpisodeIds.add(episodeId);
-      }
-    }
     _userWantsPlay = value;
     _syncPlayback();
     _notify();

lib/pages/player/widgets/player_video_surface.dart

@@ -64,9 +64,12 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface> {
           key: Key('player-fallback-background'),
           color: AppColors.mediaBlack,
         ),
-        if (!reveal && widget.openingFrame != null)
+        if (widget.openingFrame != null)
-          KeyedSubtree(
+          AnimatedOpacity(
             key: const Key('player-opening-frame'),
+            opacity: reveal ? 0 : 1,
+            duration: handoff != null ? Duration.zero : _videoFadeDuration,
+            curve: Curves.easeOut,
             child: widget.openingFrame!,
           ),
         AnimatedOpacity(

test/playback/playback_preload_test.dart

@@ -174,7 +174,7 @@ void main() {
     await session.close();
   });
 
-  test('should_keep_manual_pause_when_returning_to_same_episode', () async {
+  test('should_auto_play_previous_after_switching_from_paused_episode', () async {
     final factory = _Factory();
     final session = PlaybackSession(
       episodes: episodes,
@@ -195,13 +195,16 @@ void main() {
       factory.players.firstWhere((player) => player.id == 'ep-2').playing,
       isTrue,
     );
+    session.setUserWantsPlay(false);
+    await session.playbackSettled;
+    expect(session.userWantsPlay, isFalse);
 
     await session.select(1, preloadIndex: 2, previousIndex: 0);
     await session.preloadSettled;
-    expect(session.userWantsPlay, isFalse);
+    expect(session.userWantsPlay, isTrue);
     expect(
       factory.players.firstWhere((player) => player.id == 'ep-1').playing,
-      isFalse,
+      isTrue,
     );
     await session.close();
   });

test/player/player_opening_frame_test.dart

@@ -83,6 +83,34 @@ void main() {
 
     expect(find.byKey(const Key('player-opening-poster')), findsOneWidget);
   });
+
+  testWidgets('should_reuse_decoded_sprite_when_parent_rebuilds', (
+    tester,
+  ) async {
+    final loader = _FakeSpriteLoader();
+    final cache = OpeningFrameCache();
+    addTearDown(cache.clear);
+    Widget build() => MaterialApp(
+      home: PlayerOpeningFrame(
+        thumbnailsUrl: 'https://cdn.test/thumbnails.vtt',
+        posterUrl: 'https://cdn.test/poster.jpg',
+        loader: loader,
+        cache: cache,
+      ),
+    );
+
+    await tester.pumpWidget(build());
+    await tester.pumpAndSettle();
+    expect(loader.vttCalls, 1);
+    expect(loader.spriteCalls, hasLength(1));
+
+    await tester.pumpWidget(build());
+    await tester.pumpAndSettle();
+
+    expect(loader.vttCalls, 1);
+    expect(loader.spriteCalls, hasLength(1));
+    expect(find.byKey(const Key('player-opening-sprite')), findsOneWidget);
+  });
 }
 
 class _FakeSpriteLoader implements SpriteThumbnailAssetLoader {

test/player/player_video_surface_test.dart

@@ -30,6 +30,7 @@ void main() {
 
     expect(find.byKey(const Key('player-opening-frame')), findsOneWidget);
     expect(find.byKey(const Key('fake-opening')), findsOneWidget);
+    expect(_openingOpacity(tester), 1);
     expect(_opacity(tester), 0);
   });
 
@@ -48,7 +49,7 @@ void main() {
     expect(find.byKey(const Key('player-opening-frame')), findsNothing);
   });
 
-  testWidgets('should_fade_video_in_within_200ms_after_first_frame', (
+  testWidgets('should_cross_fade_video_over_opening_frame', (
     tester,
   ) async {
     final controller = await _pumpSurface(
@@ -67,7 +68,7 @@ void main() {
     await tester.pump();
 
     expect(_opacity(tester), 1);
-    expect(find.byKey(const Key('player-opening-frame')), findsNothing);
+    expect(find.byKey(const Key('player-opening-frame')), findsOneWidget);
     expect(
       tester
           .widget<AnimatedOpacity>(
@@ -80,8 +81,12 @@ void main() {
     final halfway = _fadeValue(tester);
     expect(halfway, greaterThan(0));
     expect(halfway, lessThan(1));
+    final openingHalfway = _openingFadeValue(tester);
+    expect(openingHalfway, greaterThan(0));
+    expect(openingHalfway, lessThan(1));
     await tester.pump(const Duration(milliseconds: 100));
     expect(_fadeValue(tester), 1);
+    expect(_openingFadeValue(tester), 0);
   });
 
   testWidgets('should_show_video_error_above_retained_fallback', (
@@ -182,6 +187,14 @@ double _opacity(WidgetTester tester) {
       .opacity;
 }
 
+double _openingOpacity(WidgetTester tester) {
+  return tester
+      .widget<AnimatedOpacity>(
+        find.byKey(const Key('player-opening-frame')),
+      )
+      .opacity;
+}
+
 double _fadeValue(WidgetTester tester) {
   final fade = find.descendant(
     of: find.byKey(const Key('player-video-opacity')),
@@ -189,3 +202,11 @@ double _fadeValue(WidgetTester tester) {
   );
   return tester.widget<FadeTransition>(fade).opacity.value;
 }
+
+double _openingFadeValue(WidgetTester tester) {
+  final fade = find.descendant(
+    of: find.byKey(const Key('player-opening-frame')),
+    matching: find.byType(FadeTransition),
+  );
+  return tester.widget<FadeTransition>(fade).opacity.value;
+}