test(ensemble): regression cover Page header timer dispose

modules/ensemble/test/widget/page_header_timer_dispose_test.dart

@@ -0,0 +1,59 @@
+import 'package:ensemble/framework/data_context.dart';
+import 'package:ensemble/framework/view/page.dart';
+import 'package:ensemble/page_model.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:yaml/yaml.dart';
+
+void main() {
+  testWidgets(
+    'Page with storage-driven header disposes without timer callbacks after unmount',
+    (tester) async {
+      final doc = loadYaml(
+        '''
+View:
+  header:
+    titleText: Test
+    collapsibleHeader:
+      enabled: true
+      visible: ensemble.storage.visFlag
+    styles:
+      listenTitleBarHeightStorage: true
+      titleBarHeight: ensemble.storage.tbhKey
+  body:
+    Column:
+      children:
+        - Text:
+            text: body
+''',
+      );
+
+      final pageModel = PageModel.fromYaml(doc as YamlMap) as SinglePageModel;
+
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Builder(
+            builder: (context) => Page(
+              dataContext: DataContext(buildContext: context),
+              pageModel: pageModel,
+              onRendered: () {},
+            ),
+          ),
+        ),
+      );
+      await tester.pump();
+      await tester.pump(const Duration(milliseconds: 50));
+
+      await tester.pumpWidget(
+        const MaterialApp(home: SizedBox.shrink()),
+      );
+      await tester.pump();
+
+      // Undisposed Timer.periodic callbacks would still fire and call setState
+      // on the disposed PageState, surfacing as a FlutterError.
+      await tester.pump(const Duration(milliseconds: 400));
+
+      expect(tester.takeException(), isNull);
+    },
+  );
+}