fix(player): 使用高清首帧并稳定切集占位

test/player/player_fullscreen_test.dart

@@ -1037,6 +1037,8 @@ void main() {
           accessible: false,
           accessType: PlayTicket.coinRequired,
           unlockCoin: 30,
+          posterUrl: '/files/locked-first-frame.jpg',
+          thumbnailsUrl: '/files/locked-thumbnails.vtt',
         ),
       ),
     );
@@ -1049,6 +1051,8 @@ void main() {
     expect(find.byKey(const Key('progress-inactive')), findsOneWidget);
     expect(find.byType(Slider), findsNothing);
     expect(find.byKey(const Key('player-single-placeholder')), findsNothing);
+    expect(find.byKey(const Key('player-opening-poster')), findsNothing);
+    expect(find.byKey(const Key('player-opening-sprite')), findsNothing);
     expect(find.byKey(const Key('player-video-crossfade')), findsNothing);
     expect(find.byKey(const Key('player-video-layer')), findsNothing);
     expect(
@@ -1487,6 +1491,8 @@ const _lockedDrama = Drama(
       isFree: false,
       locked: true,
       videoUrl: 'https://example.test/locked-demo-1.mp4',
+      posterUrl: '/files/locked-first-frame.jpg',
+      thumbnailsUrl: '/files/locked-thumbnails.vtt',
     ),
     Episode(
       id: 'locked-demo-2',

test/player/player_logic_test.dart

@@ -393,6 +393,35 @@ void main() {
     expect(logic.sessionEpisodes.first.videoUrl, 'file:///local/signal-1.mp4');
   });
 
+  test('should_write_ticket_poster_url_into_session_episode', () async {
+    final logic = _logic(
+      FakeWatchHistory(),
+      playback: FakePlaybackRepository(
+        ticket: const PlayTicket(
+          episodeId: 'signal-1',
+          accessible: true,
+          accessType: PlayTicket.free,
+          playUrl: '/files/signal-1.mp4',
+          posterUrl: '/files/transcoded/signal-1/poster.jpg',
+        ),
+      ),
+    );
+    logic.attach(
+      PlayerPage(drama: _drama('signal'), initialIndex: 0),
+      isMounted: () => true,
+    );
+    logic.start(factory: _RecordingFactory().create, coordinator: PlaybackCoordinator());
+    await _drain(logic);
+
+    expect(
+      logic.sessionEpisodes.first.posterUrl,
+      '/files/transcoded/signal-1/poster.jpg',
+    );
+
+    logic.dispose();
+    await _drain(logic);
+  });
+
   group('surface flags', () {
     test('should_set_immersive_when_picture_in_picture_callback_fires', () async {
       final factory = _RecordingFactory();

test/player/player_opening_frame_test.dart

@@ -17,6 +17,53 @@ sprite_001.jpg#xywh=0,0,160,90
 ''';
 
 void main() {
+  test('should_choose_poster_before_thumbnails_when_both_are_available', () {
+    final service = SpriteThumbnailAxisService(loader: _FakeSpriteLoader());
+    addTearDown(service.dispose);
+
+    final frame =
+        playerOpeningFrame(
+              'https://cdn.test/thumbnails.vtt',
+              posterUrl: 'https://cdn.test/poster.jpg',
+              spriteSource: service,
+              fit: BoxFit.cover,
+            )
+            as PlayerOpeningFrame;
+
+    expect(frame.posterUrl, 'https://cdn.test/poster.jpg');
+    expect(frame.thumbnailsUrl, 'https://cdn.test/thumbnails.vtt');
+    expect(frame.fit, BoxFit.cover);
+    expect(
+      playerOpeningFallback(
+        posterUrl: frame.posterUrl,
+        thumbnailsUrl: frame.thumbnailsUrl,
+      ),
+      PlayerOpeningFallback.poster,
+    );
+  });
+
+  testWidgets('should_use_poster_without_decoding_sprite_when_poster_exists', (
+    tester,
+  ) async {
+    final loader = _FakeSpriteLoader();
+    final service = SpriteThumbnailAxisService(loader: loader);
+    addTearDown(service.dispose);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: PlayerOpeningFrame(
+          posterUrl: 'https://cdn.test/poster.jpg',
+          thumbnailsUrl: 'https://cdn.test/thumbnails.vtt',
+          spriteSource: service,
+        ),
+      ),
+    );
+
+    expect(find.byKey(const Key('player-opening-poster')), findsOneWidget);
+    expect(find.byKey(const Key('player-opening-sprite')), findsNothing);
+    expect(loader.vttCalls, 0);
+  });
+
   testWidgets('should_return_no_opening_frame_when_thumbnails_is_empty', (
     tester,
   ) async {