fix(player): 优化上下滑切集黑屏

lib/pages/player/player_logic.dart

@@ -299,6 +299,7 @@ class PlayerLogic extends ChangeNotifier {
       session.remapCurrentIndex(
         keepIndex,
         preloadIndex: nextVisibleIndex(keepIndex),
+        previousIndex: previousVisibleIndex(keepIndex),
       );
       _jumpToFeedPage(keepIndex);
       _notifyAfterFrameIfNeeded();
@@ -530,6 +531,7 @@ class PlayerLogic extends ChangeNotifier {
       if (done.isCompleted) return;
       if (value.hasError || !value.isBuffering) done.complete();
     }
+
     controller.addListener(onChange);
     try {
       await done.future.timeout(const Duration(seconds: 4));
@@ -566,7 +568,7 @@ class PlayerLogic extends ChangeNotifier {
       }
       final ready = await ensureTicket(index, forceRefresh: true);
       if (ready) {
-        await session.select(index, preloadIndex: nextVisibleIndex(index));
+        await _selectVisible(index);
       }
       return ready;
     } finally {
@@ -968,7 +970,16 @@ class PlayerLogic extends ChangeNotifier {
       return;
     }
     if (!ready && ticketError != null) return;
-    await session.select(index, preloadIndex: nextVisibleIndex(index));
+    await _selectVisible(index);
+  }
+
+  /// 按可见队列选择一集，并预热上一集与下一集。
+  Future<void> _selectVisible(int index) {
+    return session.select(
+      index,
+      preloadIndex: nextVisibleIndex(index),
+      previousIndex: previousVisibleIndex(index),
+    );
   }
 
   int? nextVisibleIndex(int index) {
@@ -978,6 +989,13 @@ class PlayerLogic extends ChangeNotifier {
         : null;
   }
 
+  /// 可见队列里当前集的上一集；已经是第一集时为空。
+  int? previousVisibleIndex(int index) {
+    final position = visibleIndices.indexOf(index);
+    if (position <= 0) return null;
+    return visibleIndices[position - 1];
+  }
+
   bool get hasNextEpisode => nextVisibleIndex(session.currentIndex) != null;
 
   Future<void> playNextEpisode() async {