feat: add app lifecycle observer to pause and resume presubmit timer

dashboard/lib/state/presubmit.dart

@@ -519,6 +519,17 @@ class PresubmitState extends ChangeNotifier {
         false;
   }
 
+  void resume() {
+    if (!_active) return;
+    _startTimer();
+    _fetchRefreshUpdate();
+  }
+
+  void pause() {
+    refreshTimer?.cancel();
+    refreshTimer = null;
+  }
+
   void _fetchRefreshUpdate() {
     if (!_active) return;
     fetchIfNeeded();

dashboard/lib/views/presubmit_view.dart

@@ -42,9 +42,16 @@ final class PreSubmitView extends StatefulWidget {
   State<PreSubmitView> createState() => _PreSubmitViewState();
 }
 
-class _PreSubmitViewState extends State<PreSubmitView> {
+class _PreSubmitViewState extends State<PreSubmitView>
+    with WidgetsBindingObserver {
   PresubmitState? _presubmitState;
 
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addObserver(this);
+  }
+
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
@@ -59,10 +66,20 @@ class _PreSubmitViewState extends State<PreSubmitView> {
 
   @override
   void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
     _presubmitState?.removeListener(_onStateChanged);
     super.dispose();
   }
 
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (state == AppLifecycleState.resumed) {
+      _presubmitState?.resume();
+    } else {
+      _presubmitState?.pause();
+    }
+  }
+
   @override
   void didUpdateWidget(PreSubmitView oldWidget) {
     super.didUpdateWidget(oldWidget);

dashboard/test/state/presubmit_test.dart

@@ -267,6 +267,17 @@ void main() {
     expect(presubmitState.refreshTimer?.isActive, isFalse);
   });
 
+  test('PresubmitState pause and resume timer management', () async {
+    presubmitState.addListener(() {}); // Trigger timer start
+    expect(presubmitState.refreshTimer, isNotNull);
+
+    presubmitState.pause();
+    expect(presubmitState.refreshTimer, isNull);
+
+    presubmitState.resume();
+    expect(presubmitState.refreshTimer, isNotNull);
+  });
+
   test(
     'PresubmitState refreshes on auth change when becoming authenticated',
     () async {

dashboard/test/views/presubmit_view_test.dart

@@ -281,82 +281,94 @@ void main() {
     expect(find.textContaining('Status: Failed'), findsOneWidget);
   });
 
-  testWidgets('PreSubmitView displays default job details when summary is empty', (
-    WidgetTester tester,
-  ) async {
-    tester.view.physicalSize = const Size(2000, 1080);
-    tester.view.devicePixelRatio = 1.0;
-    addTearDown(tester.view.resetPhysicalSize);
-    addTearDown(tester.view.resetDevicePixelRatio);
-
-    const mockSha = 'decaf_3_real_sha';
-    const guardResponse = PresubmitGuardResponse(
-      prNum: 123,
-      author: 'dash',
-      guardStatus: GuardStatus.failed,
-      checkRunId: 456,
-      stages: [
-        PresubmitGuardStage(
-          name: 'Engine',
-          createdAt: 0,
-          builds: {'Mac mac_host_engine 1': TaskStatus.failed},
-        ),
-      ],
-    );
+  testWidgets(
+    'PreSubmitView displays default job details when summary is empty',
+    (WidgetTester tester) async {
+      tester.view.physicalSize = const Size(2000, 1080);
+      tester.view.devicePixelRatio = 1.0;
+      addTearDown(tester.view.resetPhysicalSize);
+      addTearDown(tester.view.resetDevicePixelRatio);
 
-    when(
-      mockCocoonService.fetchPresubmitGuard(
-        repo: anyNamed('repo'),
-        sha: mockSha,
-      ),
-    ).thenAnswer((_) async => const CocoonResponse.data(guardResponse));
+      const mockSha = 'decaf_3_real_sha';
+      const guardResponse = PresubmitGuardResponse(
+        prNum: 123,
+        author: 'dash',
+        guardStatus: GuardStatus.failed,
+        checkRunId: 456,
+        stages: [
+          PresubmitGuardStage(
+            name: 'Engine',
+            createdAt: 0,
+            builds: {'Mac mac_host_engine 1': TaskStatus.failed},
+          ),
+        ],
+      );
 
-    when(
-      mockCocoonService.fetchPresubmitJobDetails(
-        checkRunId: anyNamed('checkRunId'),
-        jobName: argThat(contains('mac_host_engine'), named: 'jobName'),
-      ),
-    ).thenAnswer(
-      (_) async => CocoonResponse.data([
-        PresubmitJobResponse(
-          attemptNumber: 1,
-          jobName: 'Mac mac_host_engine 1',
-          creationTime: 0,
-          status: TaskStatus.failed,
-          summary: '', // Empty summary
+      when(
+        mockCocoonService.fetchPresubmitGuard(
+          repo: anyNamed('repo'),
+          sha: mockSha,
         ),
-      ]),
-    );
+      ).thenAnswer((_) async => const CocoonResponse.data(guardResponse));
 
-    await tester.runAsync(() async {
-      await tester.pumpWidget(
-        createPreSubmitView({'repo': 'flutter', 'pr': '123'}),
+      when(
+        mockCocoonService.fetchPresubmitJobDetails(
+          checkRunId: anyNamed('checkRunId'),
+          jobName: argThat(contains('mac_host_engine'), named: 'jobName'),
+        ),
+      ).thenAnswer(
+        (_) async => CocoonResponse.data([
+          PresubmitJobResponse(
+            attemptNumber: 1,
+            jobName: 'Mac mac_host_engine 1',
+            creationTime: 0,
+            status: TaskStatus.failed,
+            summary: '', // Empty summary
+          ),
+        ]),
       );
-      for (var i = 0; i < 50; i++) {
-        await tester.pump();
-        await Future<void>.delayed(const Duration(milliseconds: 50));
-        if (find.textContaining('by dash').evaluate().isNotEmpty) break;
-      }
-    });
-    await tester.pumpAndSettle();
 
-    expect(find.textContaining('PR #123'), findsOneWidget);
+      await tester.runAsync(() async {
+        await tester.pumpWidget(
+          createPreSubmitView({'repo': 'flutter', 'pr': '123'}),
+        );
+        for (var i = 0; i < 50; i++) {
+          await tester.pump();
+          await Future<void>.delayed(const Duration(milliseconds: 50));
+          if (find.textContaining('by dash').evaluate().isNotEmpty) break;
+        }
+      });
+      await tester.pumpAndSettle();
 
-    await tester.tap(find.textContaining('mac_host_engine').first);
-    await tester.runAsync(() async {
-      for (var i = 0; i < 50; i++) {
-        await tester.pump();
-        await Future<void>.delayed(const Duration(milliseconds: 50));
-        if (find.textContaining('Mac mac_host_engine 1 failed.').evaluate().isNotEmpty) {
-          break;
+      expect(find.textContaining('PR #123'), findsOneWidget);
+
+      await tester.tap(find.textContaining('mac_host_engine').first);
+      await tester.runAsync(() async {
+        for (var i = 0; i < 50; i++) {
+          await tester.pump();
+          await Future<void>.delayed(const Duration(milliseconds: 50));
+          if (find
+              .textContaining('Mac mac_host_engine 1 failed.')
+              .evaluate()
+              .isNotEmpty) {
+            break;
+          }
         }
-      }
-    });
-    await tester.pumpAndSettle();
+      });
+      await tester.pumpAndSettle();
 
-    expect(find.textContaining('Mac mac_host_engine 1 failed.'), findsOneWidget);
-    expect(find.textContaining('Click "View more details on LUCI UI" button below for more details.'), findsOneWidget);
-  });
+      expect(
+        find.textContaining('Mac mac_host_engine 1 failed.'),
+        findsOneWidget,
+      );
+      expect(
+        find.textContaining(
+          'Click "View more details on LUCI UI" button below for more details.',
+        ),
+        findsOneWidget,
+      );
+    },
+  );
 
   testWidgets(
     'PreSubmitView automatically selects latest SHA and updates sidebar when opened with PR only',