fix(todo): the permission to notify asked wherever a reminder is planned, and Settings saying while it is off (ADR 0033, D31)

On a fresh install Todo's reminders never showed: the permission to notify
(Android 13's POST_NOTIFICATIONS, iOS' and macOS' alert) was asked only
where a task's sheet chose its first reminder, so reminders typed in quick
add, added by the automatic reminder or brought by sync were scheduled and
dropped by the system without a word.

Now NotificationAccess, the device's, reads whether notifications are
allowed whenever the plan holds a reminder and asks where they aren't,
once an app start, so that a refusal isn't met with the dialog again and
again; the task sheet asks through it. While reminders are planned and
notifications are off, Settings' Reminders say so, with Turn on: asked
again, and where that doesn't allow it, the system's notification settings
of the app opened (flutter_local_notifications' own call, nothing added).
Read again whenever the app comes back.

Whats-New: Todo asks to notify as soon as there is a reminder, and Settings › Reminders shows when notifications are off, with Turn on.
Whats-New-De: Todo fragt nach Benachrichtigungen, sobald es eine Erinnerung gibt, und Einstellungen › Erinnerungen zeigt, wenn sie aus sind, mit Einschalten.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/todo/halkyon_todo_flutter/lib/l10n/app_de.arb

@@ -254,6 +254,9 @@
   "snoozeTitle": "Schlummern für",
   "snoozeMinutes": "{count, plural, =1{1 Minute} other{{count} Minuten}}",
   "reminderSnooze": "{count} Min. schlummern",
+  "notificationsOffTitle": "Benachrichtigungen sind aus",
+  "notificationsOffHint": "Erinnerungen erscheinen erst, wenn Halkyon Todo dich benachrichtigen darf.",
+  "notificationsTurnOn": "Einschalten",
   "monthMore": "{count} weitere",
   "dayHeadingPattern": "EEEE, d. MMM",
   "overdueHide": "Überfälliges ausblenden",

apps/todo/halkyon_todo_flutter/lib/l10n/app_en.arb

@@ -812,6 +812,18 @@
       }
     }
   },
+  "notificationsOffTitle": "Notifications are off",
+  "@notificationsOffTitle": {
+    "description": "Settings' Reminders while notifications are off and reminders are planned (ADR 0033, D31)."
+  },
+  "notificationsOffHint": "Reminders can't show until Halkyon Todo may notify you.",
+  "@notificationsOffHint": {
+    "description": "Settings' Reminders while notifications are off and reminders are planned (ADR 0033, D31)."
+  },
+  "notificationsTurnOn": "Turn on",
+  "@notificationsTurnOn": {
+    "description": "Settings' Reminders while notifications are off and reminders are planned (ADR 0033, D31)."
+  },
   "monthMore": "{count} more",
   "@monthMore": {
     "description": "A project's Calendar as a month on wide windows (ADR 0033, D17): a day's tasks that don't fit.",

apps/todo/halkyon_todo_flutter/lib/l10n/app_localizations.dart

@@ -1624,6 +1624,24 @@ abstract class AppLocalizations {
   /// **'Snooze {count} min'**
   String reminderSnooze(int count);
 
+  /// Settings' Reminders while notifications are off and reminders are planned (ADR 0033, D31).
+  ///
+  /// In en, this message translates to:
+  /// **'Notifications are off'**
+  String get notificationsOffTitle;
+
+  /// Settings' Reminders while notifications are off and reminders are planned (ADR 0033, D31).
+  ///
+  /// In en, this message translates to:
+  /// **'Reminders can\'t show until Halkyon Todo may notify you.'**
+  String get notificationsOffHint;
+
+  /// Settings' Reminders while notifications are off and reminders are planned (ADR 0033, D31).
+  ///
+  /// In en, this message translates to:
+  /// **'Turn on'**
+  String get notificationsTurnOn;
+
   /// A project's Calendar as a month on wide windows (ADR 0033, D17): a day's tasks that don't fit.
   ///
   /// In en, this message translates to:

apps/todo/halkyon_todo_flutter/lib/l10n/app_localizations_de.dart

@@ -1006,6 +1006,16 @@ class AppLocalizationsDe extends AppLocalizations {
     return '$count Min. schlummern';
   }
 
+  @override
+  String get notificationsOffTitle => 'Benachrichtigungen sind aus';
+
+  @override
+  String get notificationsOffHint =>
+      'Erinnerungen erscheinen erst, wenn Halkyon Todo dich benachrichtigen darf.';
+
+  @override
+  String get notificationsTurnOn => 'Einschalten';
+
   @override
   String monthMore(int count) {
     return '$count weitere';

apps/todo/halkyon_todo_flutter/lib/l10n/app_localizations_en.dart

@@ -1006,6 +1006,16 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Snooze $count min';
   }
 
+  @override
+  String get notificationsOffTitle => 'Notifications are off';
+
+  @override
+  String get notificationsOffHint =>
+      'Reminders can\'t show until Halkyon Todo may notify you.';
+
+  @override
+  String get notificationsTurnOn => 'Turn on';
+
   @override
   String monthMore(int count) {
     return '$count more';

apps/todo/halkyon_todo_flutter/lib/src/app/todo_dependencies.dart

@@ -15,6 +15,7 @@ import 'package:halkyon_todo_flutter/src/feature/label/data/sync_label_gateway.d
 import 'package:halkyon_todo_flutter/src/feature/project/data/project_repository.dart';
 import 'package:halkyon_todo_flutter/src/feature/project/data/sync_project_gateway.dart';
 import 'package:halkyon_todo_flutter/src/feature/project/model/project_tree.dart';
+import 'package:halkyon_todo_flutter/src/feature/reminder/data/notification_access.dart';
 import 'package:halkyon_todo_flutter/src/feature/reminder/data/reminder_gateway.dart';
 import 'package:halkyon_todo_flutter/src/feature/reminder/data/system_reminder_gateway.dart';
 import 'package:halkyon_todo_flutter/src/feature/section/data/section_repository.dart';
@@ -61,8 +62,16 @@ class TodoPerson(
   /// The device's notifications, where their tasks' reminders go (ADR
   /// 0033, D5); none in tests that don't say.
   final ReminderGateway reminders = const NoReminders(),
+
+  /// Whether the device may show their reminders, asked once an app start
+  /// (D31): the device's, where it is given; else one of their own.
+  final NotificationAccess? _notifications,
   final Future<void> Function()? _onDispose,
 }) implements Disposable {
+  /// Whether the device may show their reminders (ADR 0033, D31).
+  late final NotificationAccess notifications =
+      _notifications ?? NotificationAccess(reminders);
+
   /// Deletes the project [id] with its sections and tasks, and its
   /// sub-projects with theirs, as Todoist does (ADR 0033, D28); throws
   /// [InboxKept] for the Inbox, which keeps everything.
@@ -274,6 +283,7 @@ class TodoDependencies({
             await folders.openOnly(person.authUserId),
             accountKeys: () => accountKeys.read(person.authUserId),
             reminders: device.reminders,
+            notifications: device.notifications,
             onClosed: closed.complete,
           );
         } on Object {
@@ -311,6 +321,7 @@ Future<TodoPerson> _openPersonData(
   Directory folder, {
   required Future<UnlockedAccountKeys?> Function() accountKeys,
   required ReminderGateway reminders,
+  required NotificationAccess notifications,
   required void Function() onClosed,
 }) async {
   final db = await client.createSyncSession(
@@ -368,6 +379,7 @@ Future<TodoPerson> _openPersonData(
     labels: labels,
     settings: settings,
     reminders: reminders,
+    notifications: notifications,
     onDispose: () async {
       try {
         await projects.dispose();
@@ -405,6 +417,10 @@ class TodoDevice({
   /// The system's notifications, where reminders go (ADR 0033, D5).
   final ReminderGateway reminders = const NoReminders(),
 }) {
+  /// Whether the device may show reminders, asked once an app start,
+  /// whoever is signed in (D31).
+  late final NotificationAccess notifications = NotificationAccess(reminders);
+
   /// Makes them, [builtIn] being the instance the build names.
   static Future<TodoDevice> create({required Instance builtIn}) async {
     final package = await PackageInfo.fromPlatform();

apps/todo/halkyon_todo_flutter/lib/src/feature/reminder/data/notification_access.dart

@@ -0,0 +1,68 @@
+import 'package:flutter/foundation.dart';
+import 'package:halkyon_todo_flutter/src/feature/reminder/data/reminder_gateway.dart';
+
+/// Whether the device may show the reminders it plans (ADR 0033, D31): asked
+/// for wherever a reminder is planned, typed in quick add, added by the
+/// automatic reminder, chosen in a task's sheet or brought by sync, once an
+/// app start, so that a person who refused isn't asked again and again
+/// (Android itself stops asking after two refusals, iOS after one); and
+/// while reminders are planned and notifications are off, Settings says so
+/// ([off]) and offers to turn them on ([turnOn]).
+///
+/// One for the device, made with its [ReminderGateway]: the app start, not
+/// the person, counts.
+class NotificationAccess(final ReminderGateway _gateway)
+    extends ChangeNotifier {
+  bool _asked = false;
+  bool _planned = false;
+  bool? _allowed;
+
+  /// Whether reminders are planned and the device may not show them.
+  bool get off => _planned && _allowed == false;
+
+  /// The plan holds reminders ([any]) or none: where it holds some, whether
+  /// the device may notify is read again (the person may have changed it in
+  /// the system's settings meanwhile), and where it may not, the person is
+  /// asked, unless they were since the app started.
+  Future<void> planned({required bool any}) async {
+    if (any != _planned) {
+      _planned = any;
+      notifyListeners();
+    }
+    if (!any) {
+      return;
+    }
+    final allowed = await _gateway.notificationsAllowed();
+    if (allowed || _asked) {
+      _set(allowed);
+      return;
+    }
+    _asked = true;
+    _set(await _gateway.askPermission());
+  }
+
+  /// Asks the person to let the app notify, where the system still asks;
+  /// whether it may.
+  Future<bool> ask() async {
+    _asked = true;
+    final allowed = await _gateway.askPermission();
+    _set(allowed);
+    return allowed;
+  }
+
+  /// Settings' Turn on: asks again, and where that doesn't allow it (refused
+  /// again, or the system asks no more), opens the system's notification
+  /// settings of the app, where the person can turn them on.
+  Future<void> turnOn() async {
+    if (!await ask()) {
+      await _gateway.openSettings();
+    }
+  }
+
+  void _set(bool allowed) {
+    if (allowed != _allowed) {
+      _allowed = allowed;
+      notifyListeners();
+    }
+  }
+}

apps/todo/halkyon_todo_flutter/lib/src/feature/reminder/data/reminder_gateway.dart

@@ -16,9 +16,17 @@ abstract interface class ReminderGateway() {
     ({int minutes, String label})? snooze,
   });
 
+  /// Whether the app may show notifications now (ADR 0033, D31): on
+  /// Android 13 on, iOS and macOS not until the person allows it.
+  Future<bool> notificationsAllowed();
+
   /// Asks the person to let the app show notifications, where the system
   /// asks; whether it may.
   Future<bool> askPermission();
+
+  /// Opens the system's notification settings of the app, where the person
+  /// turns them on once the system no longer asks (D31).
+  Future<void> openSettings();
 }
 
 /// No reminders at all: a device or test without notifications.
@@ -30,6 +38,13 @@ class const NoReminders() implements ReminderGateway {
     ({int minutes, String label})? snooze,
   }) async {}
 
+  /// Nothing to turn on: nothing is shown either way.
+  @override
+  Future<bool> notificationsAllowed() async => true;
+
   @override
   Future<bool> askPermission() async => false;
+
+  @override
+  Future<void> openSettings() async {}
 }

apps/todo/halkyon_todo_flutter/lib/src/feature/reminder/data/system_reminder_gateway.dart

@@ -201,7 +201,7 @@ class SystemReminderGateway(final FlutterLocalNotificationsPlugin _plugin)
       onDidReceiveBackgroundNotificationResponse: snoozeInBackground,
       settings: InitializationSettings(
         android: const AndroidInitializationSettings('@mipmap/ic_launcher'),
-        // Asked for when the person first adds a reminder, not at start.
+        // Asked for once a reminder is planned (D31), not at start.
         iOS: DarwinInitializationSettings(
           requestAlertPermission: false,
           requestBadgePermission: false,
@@ -291,14 +291,14 @@ class SystemReminderGateway(final FlutterLocalNotificationsPlugin _plugin)
     }
   }
 
-  /// Whether Android lets the app wake at the minute (its exact alarms,
-  /// which Android 14 leaves off until the person allows them in the
-  /// system's settings); elsewhere it always does.
+  /// Whether Android lets the app wake at the minute (ADR 0033, D31): on
+  /// Android 13 on through `USE_EXACT_ALARM`, granted with the install to
+  /// an app that reminds of what a person planned, on 12 and 12L through
+  /// `SCHEDULE_EXACT_ALARM`, granted unless the person took it back (the
+  /// manifest declares it up to API 32); `AlarmManager.canScheduleExactAlarms`
+  /// is true with either. Elsewhere it always does.
   Future<bool> _exact() async {
-    final android = _plugin
-        .resolvePlatformSpecificImplementation<
-          AndroidFlutterLocalNotificationsPlugin
-        >();
+    final android = _android;
     return android == null ||
         (await android.canScheduleExactNotifications() ?? false);
   }
@@ -329,31 +329,65 @@ class SystemReminderGateway(final FlutterLocalNotificationsPlugin _plugin)
     }
   }
 
+  AndroidFlutterLocalNotificationsPlugin? get _android => _plugin
+      .resolvePlatformSpecificImplementation<
+        AndroidFlutterLocalNotificationsPlugin
+      >();
+
+  IOSFlutterLocalNotificationsPlugin? get _iOS => _plugin
+      .resolvePlatformSpecificImplementation<
+        IOSFlutterLocalNotificationsPlugin
+      >();
+
+  MacOSFlutterLocalNotificationsPlugin? get _macOS => _plugin
+      .resolvePlatformSpecificImplementation<
+        MacOSFlutterLocalNotificationsPlugin
+      >();
+
+  @override
+  Future<bool> notificationsAllowed() async {
+    try {
+      return switch (defaultTargetPlatform) {
+        TargetPlatform.android =>
+          await _android?.areNotificationsEnabled() ?? false,
+        TargetPlatform.iOS =>
+          (await _iOS?.checkPermissions())?.isEnabled ?? false,
+        TargetPlatform.macOS =>
+          (await _macOS?.checkPermissions())?.isEnabled ?? false,
+        // Linux and Windows ask nothing of an app before it notifies.
+        _ => true,
+      };
+    } on Object catch (error) {
+      log('Notifications not known: $error', name: 'Reminders');
+      // Not known: nothing asked, nothing said.
+      return true;
+    }
+  }
+
+  @override
+  Future<void> openSettings() async {
+    try {
+      await switch (defaultTargetPlatform) {
+        TargetPlatform.android => _android?.openAppNotificationSettings(),
+        TargetPlatform.iOS => _iOS?.openAppNotificationSettings(),
+        TargetPlatform.macOS => _macOS?.openAppNotificationSettings(),
+        _ => null,
+      };
+    } on Object catch (error) {
+      log('Notification settings not opened: $error', name: 'Reminders');
+    }
+  }
+
   @override
   Future<bool> askPermission() async {
     try {
       return switch (defaultTargetPlatform) {
         TargetPlatform.android =>
-          await _plugin
-                  .resolvePlatformSpecificImplementation<
-                    AndroidFlutterLocalNotificationsPlugin
-                  >()
-                  ?.requestNotificationsPermission() ??
-              false,
+          await _android?.requestNotificationsPermission() ?? false,
         TargetPlatform.iOS =>
-          await _plugin
-                  .resolvePlatformSpecificImplementation<
-                    IOSFlutterLocalNotificationsPlugin
-                  >()
-                  ?.requestPermissions(alert: true, sound: true) ??
-              false,
+          await _iOS?.requestPermissions(alert: true, sound: true) ?? false,
         TargetPlatform.macOS =>
-          await _plugin
-                  .resolvePlatformSpecificImplementation<
-                    MacOSFlutterLocalNotificationsPlugin
-                  >()
-                  ?.requestPermissions(alert: true, sound: true) ??
-              false,
+          await _macOS?.requestPermissions(alert: true, sound: true) ?? false,
         _ => true,
       };
     } on Object catch (error) {

apps/todo/halkyon_todo_flutter/lib/src/feature/reminder/widget/reminder_scheduler.dart

@@ -16,7 +16,9 @@ import 'package:material_ui/material_ui.dart';
 /// D5): planned again whenever the tasks change, here or through sync,
 /// when the app comes back to the front, and every few hours as the
 /// planned weeks move on; handed to the system only where the plan, or how
-/// long a reminder is snoozed for (D4), changed.
+/// long a reminder is snoozed for (D4), changed. Where the plan holds a
+/// reminder, the person is asked to let the app notify (D31,
+/// `NotificationAccess`).
 class const ReminderScheduler({required final Widget child, super.key})
     extends StatefulWidget {
   @override
@@ -57,6 +59,14 @@ class _ReminderSchedulerState() extends State<ReminderScheduler> {
     final plan = planReminders([
       for (final task in state.tasks) StoredTask(task.id, task.content),
     ], now: clock.now());
+    // Asked to notify wherever the reminders came from (D31): typed, added
+    // by the automatic reminder, chosen in a sheet or synced; and read
+    // again as the app comes back, from the system's settings perhaps.
+    unawaited(
+      PersonScope.of<TodoPerson>(
+        context,
+      ).notifications.planned(any: plan.isNotEmpty),
+    );
     final snooze = state.settings.reminders.snooze;
     if (listEquals(plan, _planned) && snooze == _snooze) {
       return;

apps/todo/halkyon_todo_flutter/lib/src/feature/task/widget/task_sheet.dart

@@ -840,9 +840,10 @@ class _TaskSheetState() extends State<_TaskSheet> {
         (timed && content.reminders.isNotEmpty) ||
         content.reminderTimes.isNotEmpty;
     if (!had && (chosen.before.isNotEmpty || chosen.at.isNotEmpty)) {
-      final reminders = PersonScope.of<TodoPerson>(context).reminders;
+      // Through the device's ask (D31), so that the plan's doesn't follow.
+      final notifications = PersonScope.of<TodoPerson>(context).notifications;
       final messenger = ScaffoldMessenger.of(context);
-      if (!await reminders.askPermission()) {
+      if (!await notifications.ask()) {
         messenger.showSnackBar(
           SnackBar(content: Text(l10n.remindersNotAllowed)),
         );

apps/todo/halkyon_todo_flutter/lib/src/settings/todo_settings_cards.dart

@@ -79,7 +79,9 @@ class const TaskSettingsCard({super.key}) extends StatelessWidget {
 
 /// Settings' *Reminders* (D4): the automatic reminder a task given a time
 /// gets where it has none of its own (none at first), and how long a
-/// reminder is snoozed for from its notification.
+/// reminder is snoozed for from its notification; above them, while
+/// reminders are planned and the device may not show them, that
+/// notifications are off, with Turn on (D31).
 class const ReminderSettingsCard({super.key}) extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
@@ -94,6 +96,7 @@ class const ReminderSettingsCard({super.key}) extends StatelessWidget {
     return _Card(
       title: l10n.remindersTitle,
       children: [
+        const _NotificationsOff(),
         ListTile(
           leading: const Icon(LucideIcons.alarmClockPlus),
           title: ExplainedTitle(
@@ -146,6 +149,36 @@ class const ReminderSettingsCard({super.key}) extends StatelessWidget {
   }
 }
 
+/// That notifications are off while reminders are planned (D31), with Turn
+/// on: asked again, or where the system asks no more, its notification
+/// settings of the app opened; nothing while they are on, or nothing is
+/// planned.
+class const _NotificationsOff() extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+    final notifications = PersonScope.of<TodoPerson>(context).notifications;
+    return ListenableBuilder(
+      listenable: notifications,
+      builder: (context, _) {
+        if (!notifications.off) {
+          return const SizedBox.shrink();
+        }
+        final colors = Theme.of(context).colorScheme;
+        return ListTile(
+          leading: Icon(LucideIcons.bellOff, color: colors.error),
+          title: Text(l10n.notificationsOffTitle),
+          subtitle: Text(l10n.notificationsOffHint),
+          trailing: FilledButton.tonal(
+            onPressed: notifications.turnOn,
+            child: Text(l10n.notificationsTurnOn),
+          ),
+        );
+      },
+    );
+  }
+}
+
 /// A group of Settings under its [title].
 class const _Card({
   required final String title,

apps/todo/halkyon_todo_flutter/test/app/todo_app_test.dart

@@ -3926,6 +3926,146 @@ void main() {
         );
       });
     });
+
+    group('Notifications asked for wherever a reminder is planned (D31)', () {
+      /// Whether Settings' Reminders say that notifications are off.
+      Finder off() => find.text('Notifications are off');
+
+      testWidgets('a reminder typed in quick add asks to notify, once an '
+          'app start, however many follow', (tester) async {
+        reminders.allowed = false;
+        await start(tester, usedBefore: true);
+        expect(reminders.asked, 0, reason: 'nothing to remind of yet');
+        await goTab(tester, 'Inbox');
+
+        await quickAdd(tester, 'Leave !30m');
+        expect(reminders.scheduled, hasLength(1));
+        expect(reminders.asked, 1);
+
+        await quickAdd(tester, 'Call back !1h');
+        expect(reminders.scheduled, hasLength(2));
+        expect(reminders.asked, 1, reason: 'refused once, not asked again');
+      });
+
+      testWidgets('the automatic reminder of a task given a time asks to '
+          'notify', (tester) async {
+        await start(tester, usedBefore: true);
+        await tester.runAsync(
+          () => SettingsRepository(settingsRows, keys).write(
+            const TodoSettings(reminders: ReminderSettings(automatic: 15)),
+          ),
+        );
+        settingsRows.bringRemoteChanges();
+        await tester.pumpAndSettle();
+        await goTab(tester, 'Inbox');
+
+        await quickAdd(tester, 'Call tomorrow 9am');
+
+        expect(reminders.scheduled, hasLength(1));
+        expect(reminders.asked, 1);
+        expect(reminders.enabled, isTrue);
+      });
+
+      testWidgets('a reminder another device synced asks to notify; nothing '
+          'is asked where none is planned', (tester) async {
+        final tomorrow = Day.of(DateTime.now()).plus(1);
+        await start(tester, usedBefore: true);
+        await seed(
+          tester,
+          TaskContent(
+            title: 'Call the bank',
+            projectId: inbox(),
+            date: TaskDate(tomorrow, time: 14 * 60),
+          ),
+        );
+        await goTab(tester, 'Inbox');
+        await quickAdd(tester, 'Buy milk');
+        expect(reminders.asked, 0, reason: 'nothing to remind of');
+        await openSettings(tester);
+        expect(off(), findsNothing, reason: 'no reminder needs them');
+        await tester.pageBack();
+        await tester.pumpAndSettle();
+
+        await seed(
+          tester,
+          TaskContent(
+            title: 'Dentist',
+            projectId: inbox(),
+            date: TaskDate(tomorrow, time: 9 * 60),
+            reminders: const [30],
+          ),
+        );
+
+        expect(reminders.asked, 1);
+      });
+
+      testWidgets("refused, Settings' Reminders say notifications are off; "
+          "Turn on asks again, then opens the system's settings, and "
+          'notifications allowed there count once Todo is back', (
+        tester,
+      ) async {
+        final tomorrow = Day.of(DateTime.now()).plus(1);
+        reminders.allowed = false;
+        await start(tester, usedBefore: true);
+        await seed(
+          tester,
+          TaskContent(
+            title: 'Dentist',
+            projectId: inbox(),
+            date: TaskDate(tomorrow, time: 9 * 60),
+            reminders: const [30],
+          ),
+        );
+        expect(reminders.asked, 1);
+
+        await openSettings(tester);
+        expect(off(), findsOneWidget);
+        await tester.tap(find.widgetWithText(FilledButton, 'Turn on'));
+        await tester.pumpAndSettle();
+        expect(reminders.asked, 2);
+        expect(
+          reminders.openedSettings,
+          1,
+          reason: 'refused again, or the system no longer asks',
+        );
+        expect(off(), findsOneWidget);
+
+        // Allowed in the system's settings, then back to Todo.
+        reminders.enabled = true;
+        tester.binding
+          ..handleAppLifecycleStateChanged(AppLifecycleState.inactive)
+          ..handleAppLifecycleStateChanged(AppLifecycleState.resumed);
+        await tester.pumpAndSettle();
+        expect(off(), findsNothing);
+        expect(reminders.asked, 2);
+      });
+
+      testWidgets('Turn on allowed asks no more and opens nothing', (
+        tester,
+      ) async {
+        final tomorrow = Day.of(DateTime.now()).plus(1);
+        reminders.allowed = false;
+        await start(tester, usedBefore: true);
+        await seed(
+          tester,
+          TaskContent(
+            title: 'Dentist',
+            projectId: inbox(),
+            date: TaskDate(tomorrow, time: 9 * 60),
+            reminders: const [30],
+          ),
+        );
+        await openSettings(tester);
+
+        reminders.allowed = true;
+        await tester.tap(find.widgetWithText(FilledButton, 'Turn on'));
+        await tester.pumpAndSettle();
+
+        expect(reminders.asked, 2);
+        expect(reminders.openedSettings, 0);
+        expect(off(), findsNothing);
+      });
+    });
   });
 
   group("Upcoming's strip (ADR 0033, D8, D14)", () {

apps/todo/halkyon_todo_flutter/test/support/memory_reminder_gateway.dart

@@ -15,9 +15,17 @@ class MemoryReminderGateway() implements ReminderGateway {
   /// What the person answers when asked.
   bool allowed = true;
 
+  /// Whether the app may notify now: not on a fresh install until the
+  /// person is asked and allows it (Android 13 on, iOS, macOS), or allows
+  /// it in the system's settings meanwhile.
+  bool enabled = false;
+
   /// How often they were asked.
   int asked = 0;
 
+  /// How often the system's notification settings of the app were opened.
+  int openedSettings = 0;
+
   @override
   Future<void> replace(
     List<ReminderNotice> notices, {
@@ -29,9 +37,17 @@ class MemoryReminderGateway() implements ReminderGateway {
     replaced++;
   }
 
+  @override
+  Future<bool> notificationsAllowed() async => enabled;
+
   @override
   Future<bool> askPermission() async {
     asked++;
-    return allowed;
+    return enabled = allowed;
+  }
+
+  @override
+  Future<void> openSettings() async {
+    openedSettings++;
   }
 }