优化：卡片预览的稳定性

lib/features/home/home_screen.dart

@@ -41,6 +41,8 @@ class _HomeScreenState extends State<HomeScreen> {
   /// [index] -> 最近一次 visibility 回调的 [VisibilityInfo.visibleFraction]
   final Map<int, double> _cardVisibleFraction = {};
   bool _visibilityReconcileScheduled = false;
+  /// 是否曾有过「可见比例 ≥ 阈值」的探测器回调（用于区分冷启动无回调 vs 已全部滑出视口）
+  bool _visibilityHadMeaningfulReport = false;
 
   /// IndexedStack 切回首页或 [homePlaybackResumeNonce] 递增后，让 [VisibilityDetector] 重新计算。
   /// 单次 [notifyNow] 在「Modal 收起 / 子路由 pop」后首帧常过早，与 My Gallery 一致采用多帧 + 短延迟。
@@ -62,6 +64,17 @@ class _HomeScreenState extends State<HomeScreen> {
     });
     Future<void>.delayed(const Duration(milliseconds: 80), notify);
     Future<void>.delayed(const Duration(milliseconds: 220), notify);
+    // 冷启动首屏 Grid 布局/Texture 较晚就绪时，前两档仍可能拿不到可见性
+    Future<void>.delayed(const Duration(milliseconds: 450), notify);
+    Future<void>.delayed(const Duration(milliseconds: 720), notify);
+    Future<void>.delayed(const Duration(milliseconds: 950), () {
+      if (!mounted || !widget.isActive) return;
+      VisibilityDetectorController.instance.notifyNow();
+      WidgetsBinding.instance.addPostFrameCallback((_) {
+        if (!mounted || !widget.isActive) return;
+        _seedFirstScreenVideoIndicesIfStillEmpty();
+      });
+    });
   }
 
   @override
@@ -76,6 +89,21 @@ class _HomeScreenState extends State<HomeScreen> {
     if (widget.isActive) refreshAccount();
   }
 
+  void _seedFirstScreenVideoIndicesIfStillEmpty() {
+    if (!mounted || !widget.isActive) return;
+    if (_visibleVideoIndices.isNotEmpty) return;
+    if (_visibilityHadMeaningfulReport) return;
+    final tasks = _displayTasks;
+    if (tasks.isEmpty) return;
+    final seed = <int>{};
+    for (var i = 0; i < tasks.length && seed.length < _maxConcurrentHomeVideos; i++) {
+      final u = tasks[i].previewVideoUrl;
+      if (u != null && u.isNotEmpty) seed.add(i);
+    }
+    if (seed.isEmpty) return;
+    setState(() => _visibleVideoIndices = seed);
+  }
+
   @override
   void dispose() {
     homePlaybackResumeNonce.removeListener(_onHomePlaybackResumeSignal);
@@ -94,6 +122,10 @@ class _HomeScreenState extends State<HomeScreen> {
 
   void _onExtConfigChanged() {
     if (mounted) setState(() {});
+    // 不用 Timer 防抖：连续 listener 会互相 cancel，首装可能永远不触发 notify
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (mounted && widget.isActive) _scheduleVisibilityRefresh();
+    });
   }
 
   void _onHomeReloadNonce() {
@@ -110,6 +142,7 @@ class _HomeScreenState extends State<HomeScreen> {
     if (!mounted) return;
     if (info.visibleFraction >= _videoVisibilityThreshold) {
       _cardVisibleFraction[index] = info.visibleFraction;
+      _visibilityHadMeaningfulReport = true;
     } else {
       _cardVisibleFraction.remove(index);
     }
@@ -133,6 +166,16 @@ class _HomeScreenState extends State<HomeScreen> {
         scored.add(MapEntry(i, e.value));
       }
     }
+    if (scored.isEmpty) {
+      // 冷启动：探测器尚未给出 ≥ 阈值的回调时，不要用空集覆盖（否则会清掉兜底或一直不播）
+      if (!_visibilityHadMeaningfulReport) return;
+      _userPausedVideoIndices.clear();
+      if (!_setsEqual(_visibleVideoIndices, {})) {
+        setState(() => _visibleVideoIndices = {});
+      }
+      return;
+    }
+
     scored.sort((a, b) => b.value.compareTo(a.value));
     final next = scored
         .take(_maxConcurrentHomeVideos)
@@ -255,6 +298,10 @@ class _HomeScreenState extends State<HomeScreen> {
         print('HomeScreen: Failed to load categories');
       }
       setState(() => _categoriesLoading = false);
+      // 默认选中 pets 等不会走 [_loadTasks] 的路径，也要触发一次可见性（否则预览不自动播）
+      WidgetsBinding.instance.addPostFrameCallback((_) {
+        if (mounted && widget.isActive) _scheduleVisibilityRefresh();
+      });
     }
   }
 
@@ -271,6 +318,7 @@ class _HomeScreenState extends State<HomeScreen> {
           _userPausedVideoIndices.clear();
           _visibleVideoIndices = {};
           _cardVisibleFraction.clear();
+          _visibilityHadMeaningfulReport = false;
         });
       } else {
         setState(() {
@@ -278,6 +326,7 @@ class _HomeScreenState extends State<HomeScreen> {
           _userPausedVideoIndices.clear();
           _visibleVideoIndices = {};
           _cardVisibleFraction.clear();
+          _visibilityHadMeaningfulReport = false;
         });
       }
       setState(() => _tasksLoading = false);
@@ -300,6 +349,7 @@ class _HomeScreenState extends State<HomeScreen> {
         _userPausedVideoIndices.clear();
         _visibleVideoIndices = {};
         _cardVisibleFraction.clear();
+        _visibilityHadMeaningfulReport = false;
       });
       WidgetsBinding.instance.addPostFrameCallback((_) {
         if (mounted && widget.isActive) _scheduleVisibilityRefresh();