fix(home): 首切频道预取并保留播放画面

test/core/data/services/home_feed_controller_test.dart

@@ -27,6 +27,67 @@ void main() {
     },
   );
 
+  test(
+    'should_use_prefetched_channel_without_another_request_on_first_select',
+    () async {
+      final repository = _ScriptedFeedRepository()
+        ..enqueue(() async => FeedPage(dramas: [_drama('anime')]))
+        ..enqueue(() async => FeedPage(dramas: [_drama('live')]));
+      final controller = HomeFeedController(repository);
+      controller.seedRecommend([_drama('seed')]);
+
+      await controller.prefetchChannels();
+      await controller.selectChannel(HomeFeedChannel.anime);
+
+      expect(controller.dramas.single.id, 'anime');
+      expect(repository.calls.map((call) => call.types), [
+        ['ANIME'],
+        ['LIVE'],
+      ]);
+      controller.dispose();
+    },
+  );
+
+  test('should_keep_recommend_when_prefetch_fails', () async {
+    final repository = _ScriptedFeedRepository()
+      ..enqueue(() async => throw StateError('offline'))
+      ..enqueue(() async => FeedPage(dramas: [_drama('live')]));
+    final controller = HomeFeedController(repository);
+    controller.seedRecommend([_drama('seed')]);
+
+    await controller.prefetchChannels();
+
+    expect(controller.channel, HomeFeedChannel.recommend);
+    expect(controller.dramas.single.id, 'seed');
+    expect(controller.lastError, isNull);
+    controller.dispose();
+  });
+
+  test(
+    'should_wait_prefetch_without_duplicate_request_when_channel_is_selected',
+    () async {
+      final anime = Completer<FeedPage>();
+      final repository = _ScriptedFeedRepository()
+        ..enqueue(() => anime.future)
+        ..enqueue(() async => FeedPage(dramas: [_drama('live')]));
+      final controller = HomeFeedController(repository);
+      controller.seedRecommend([_drama('seed')]);
+
+      final prefetch = controller.prefetchChannels();
+      final select = controller.selectChannel(HomeFeedChannel.anime);
+      anime.complete(FeedPage(dramas: [_drama('anime')]));
+      await prefetch;
+      await select;
+
+      expect(
+        repository.calls.where((call) => call.types.contains('ANIME')),
+        hasLength(1),
+      );
+      expect(controller.dramas.single.id, 'anime');
+      controller.dispose();
+    },
+  );
+
   test('should_request_anime_live_and_recommend_with_expected_types', () async {
     final repository = _ScriptedFeedRepository()
       ..enqueue(() async => FeedPage(dramas: [_drama('anime')]))