fix(flutter): 修复剧场吸顶分类行闪烁并压缩间距

test/discover/home_all_dramas_grid_test.dart

@@ -226,6 +226,46 @@ void main() {
     expect(header().color, AppColors.ink);
   });
 
+  testWidgets('should_keep_category_row_stable_across_scrolls', (tester) async {
+    await _pumpTheater(
+      tester,
+      categoryRepository: _GridCategoryRepository(
+        discoverFeed: _tallDiscoverFeed,
+      ),
+    );
+    double categoryTop() =>
+        tester.getRect(find.byKey(const Key('theater-category-chips'))).top;
+    final initial = categoryTop();
+
+    await tester.drag(_verticalFeed, const Offset(0, -120));
+    await tester.pumpAndSettle();
+    final once = categoryTop();
+    await tester.drag(_verticalFeed, const Offset(0, -120));
+    await tester.pumpAndSettle();
+    final twice = categoryTop();
+    await tester.drag(_verticalFeed, const Offset(0, 400));
+    await tester.pumpAndSettle();
+    final backToTop = categoryTop();
+
+    expect(once, closeTo(initial, 0.5));
+    expect(twice, closeTo(initial, 0.5));
+    expect(backToTop, closeTo(initial, 0.5));
+  });
+
+  testWidgets('should_keep_small_gap_between_category_and_toolbar', (
+    tester,
+  ) async {
+    await _pumpTheater(tester, categoryRepository: _GridCategoryRepository());
+    final categoryBottom = tester
+        .getRect(find.byKey(const Key('theater-category-chips')))
+        .bottom;
+    final toolbarTop = tester
+        .getRect(find.byKey(const Key('theater-toolbar-filter')))
+        .top;
+
+    expect(toolbarTop - categoryBottom, inInclusiveRange(0, 6));
+  });
+
   testWidgets('should_show_category_underline_for_selection', (tester) async {
     await _pumpTheater(tester, categoryRepository: _GridCategoryRepository());
     Color underline(String id) =>