fix(discover): 固定发现页顶栏

test/discover/home_all_dramas_grid_test.dart

@@ -132,6 +132,43 @@ void main() {
     );
   });
 
+  testWidgets('should_keep_discover_header_fixed_when_content_scrolls', (
+    tester,
+  ) async {
+    tester.view.physicalSize = const Size(390, 844);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.resetPhysicalSize);
+    addTearDown(tester.view.resetDevicePixelRatio);
+
+    await _pumpApp(
+      tester,
+      categoryRepository: _GridCategoryRepository(
+        discoverFeed: _tallDiscoverFeed,
+      ),
+    );
+    await tester.tap(find.byKey(const Key('tab-discover')));
+    await tester.pumpAndSettle();
+
+    final headerBefore = tester.getTopLeft(
+      find.byKey(const Key('discover-search-button')),
+    );
+    final contentBefore = tester.getTopLeft(
+      find.byKey(const Key('home-category-chips')),
+    );
+
+    await tester.drag(find.byType(CustomScrollView), const Offset(0, -40));
+    await tester.pumpAndSettle();
+
+    expect(
+      tester.getTopLeft(find.byKey(const Key('discover-search-button'))),
+      headerBefore,
+    );
+    expect(
+      tester.getTopLeft(find.byKey(const Key('home-category-chips'))).dy,
+      lessThan(contentBefore.dy),
+    );
+  });
+
   testWidgets('should_keep_empty_messages_when_feed_has_no_dramas', (
     tester,
   ) async {
@@ -341,3 +378,23 @@ final _defaultDiscoverFeed = HomeFeed(
     ),
   ],
 );
+
+final _tallDiscoverFeed = HomeFeed(
+  sections: [
+    FeedSection(
+      code: 'hot',
+      title: 'Hot',
+      dramas: [
+        for (var index = 0; index < 12; index++)
+          Drama(
+            id: 'tall-$index',
+            title: 'Tall Drama $index',
+            synopsis: 'Tall Drama $index synopsis',
+            posterUrl: '/files/tall-$index.png',
+            genre: 'Urban Romance',
+            detailLoaded: true,
+          ),
+      ],
+    ),
+  ],
+);