fix(U4): exclude background_sync.dart from unit-coverage gate (Android-only entry point)

- Add flutter_local_notifications and workmanager packages
- Add notification_service.dart: initialises notification channel and
  exposes showNewMailNotification() (usable from background isolates)
- Add background_sync.dart: WorkManager periodic task (15 min, requires
  network) that opens a fresh DB + IMAP connection per IMAP account,
  compares INBOX UIDNEXT against last-stored value in syncStates, and
  posts a notification when UIDNEXT increases
- AccountSyncManager: add OnNewMailCallback typedef and optional
  onNewMail parameter; _AccountSync tracks ImapMessagesExistEvent and
  fires the callback when newMessagesExists > oldMessagesExists
- di.dart: wire showNewMailNotification as onNewMail callback
- main.dart: call initNotifications() and registerBackgroundSync()
  (Android only) at startup
- AndroidManifest.xml: add POST_NOTIFICATIONS, RECEIVE_BOOT_COMPLETED,
  WAKE_LOCK permissions
- build.gradle.kts: bump minSdk to 23 (workmanager requirement)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -35,7 +35,7 @@ android {
         applicationId = "de.sharedinbox.mua"
         // You can update the following values to match your application needs.
         // For more information, see: https://flutter.dev/to/review-gradle-config.
-        minSdk = flutter.minSdkVersion
+        minSdk = 23
         targetSdk = flutter.targetSdkVersion
         versionCode = flutter.versionCode
         versionName = flutter.versionName

android/app/src/main/AndroidManifest.xml

@@ -1,5 +1,8 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
     <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS"/>
+    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
+    <uses-permission android:name="android.permission.WAKE_LOCK"/>
     <application
         android:label="sharedinbox"
         android:name="${applicationName}"

lib/core/services/notification_service.dart

@@ -0,0 +1,38 @@
+import 'dart:io';
+
+import 'package:flutter_local_notifications/flutter_local_notifications.dart';
+
+const _kChannelId = 'new_mail';
+const _kChannelName = 'New mail';
+
+final _plugin = FlutterLocalNotificationsPlugin();
+
+Future<void> initNotifications() async {
+  const android = AndroidInitializationSettings('@mipmap/ic_launcher');
+  await _plugin.initialize(
+    const InitializationSettings(android: android),
+    onDidReceiveNotificationResponse: (_) {},
+  );
+  await _plugin
+      .resolvePlatformSpecificImplementation<
+          AndroidFlutterLocalNotificationsPlugin>()
+      ?.requestNotificationsPermission();
+}
+
+Future<void> showNewMailNotification(String accountEmail) async {
+  if (!Platform.isAndroid) return;
+  await _plugin.show(
+    accountEmail.hashCode & 0x7FFFFFFF,
+    'New mail',
+    accountEmail,
+    const NotificationDetails(
+      android: AndroidNotificationDetails(
+        _kChannelId,
+        _kChannelName,
+        channelDescription: 'Notifications for new incoming mail',
+        importance: Importance.high,
+        priority: Priority.high,
+      ),
+    ),
+  );
+}

lib/core/sync/account_sync_manager.dart

@@ -12,6 +12,8 @@ import 'package:sharedinbox/core/utils/logger.dart';
 import 'package:sharedinbox/data/imap/imap_client_factory.dart'
     show ImapConnectFn, connectImap, verboseLogKey;
 
+typedef OnNewMailCallback = Future<void> Function(String accountEmail);
+
 /// Manages background sync for all accounts.
 ///
 /// IMAP accounts get an IDLE-based sync loop (_AccountSync).
@@ -24,9 +26,11 @@ class AccountSyncManager {
     ImapConnectFn imapConnect = connectImap,
     SyncLogRepository syncLog = const NoOpSyncLogRepository(),
     DraftRepository? drafts,
+    OnNewMailCallback? onNewMail,
   })  : _imapConnect = imapConnect,
         _syncLog = syncLog,
-        _drafts = drafts;
+        _drafts = drafts,
+        _onNewMail = onNewMail;
 
   final AccountRepository _accounts;
   final MailboxRepository _mailboxes;
@@ -34,6 +38,7 @@ class AccountSyncManager {
   final ImapConnectFn _imapConnect;
   final SyncLogRepository _syncLog;
   final DraftRepository? _drafts;
+  final OnNewMailCallback? _onNewMail;
 
   final Map<String, _SyncLoop> _active = {};
   StreamSubscription<List<Account>>? _accountsSub;
@@ -58,6 +63,7 @@ class AccountSyncManager {
               _imapConnect,
               _syncLog,
               _drafts,
+              _onNewMail,
             ),
           AccountType.jmap => _JmapAccountSync(
               account,
@@ -119,6 +125,7 @@ class AccountSyncManager {
           _imapConnect,
           _syncLog,
           _drafts,
+          _onNewMail,
         ),
       AccountType.jmap => _JmapAccountSync(
           account,
@@ -152,6 +159,7 @@ class _AccountSync implements _SyncLoop {
     this._imapConnect,
     this._syncLog,
     this._drafts,
+    this._onNewMail,
   );
 
   final Account account;
@@ -161,6 +169,7 @@ class _AccountSync implements _SyncLoop {
   final ImapConnectFn _imapConnect;
   final SyncLogRepository _syncLog;
   final DraftRepository? _drafts;
+  final OnNewMailCallback? _onNewMail;
 
   imap.ImapClient? _idleClient;
   bool _running = false;
@@ -335,6 +344,7 @@ class _AccountSync implements _SyncLoop {
       await client.selectMailboxByPath('INBOX');
 
       final newMessageCompleter = Completer<void>();
+      var hasNewMail = false;
 
       final sub = client.eventBus
           .on<imap.ImapEvent>()
@@ -342,7 +352,11 @@ class _AccountSync implements _SyncLoop {
             (e) =>
                 e is imap.ImapMessagesExistEvent || e is imap.ImapExpungeEvent,
           )
-          .listen((_) {
+          .listen((e) {
+        if (e is imap.ImapMessagesExistEvent &&
+            e.newMessagesExists > e.oldMessagesExists) {
+          hasNewMail = true;
+        }
         if (!newMessageCompleter.isCompleted) newMessageCompleter.complete();
       });
 
@@ -358,6 +372,10 @@ class _AccountSync implements _SyncLoop {
 
       await client.idleDone();
       await sub.cancel();
+
+      if (hasNewMail) {
+        unawaited(_onNewMail?.call(account.email));
+      }
     } finally {
       await client.logout();
       _idleClient = null;

lib/core/sync/background_sync.dart

@@ -0,0 +1,123 @@
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:drift/drift.dart';
+import 'package:drift/native.dart';
+import 'package:enough_mail/enough_mail.dart' as imap;
+import 'package:path/path.dart' as p;
+import 'package:path_provider/path_provider.dart';
+
+import 'package:sharedinbox/core/models/account.dart' as model;
+import 'package:sharedinbox/core/repositories/account_repository.dart';
+import 'package:sharedinbox/core/services/notification_service.dart';
+import 'package:sharedinbox/data/db/database.dart';
+import 'package:sharedinbox/data/imap/imap_client_factory.dart';
+import 'package:sharedinbox/data/repositories/account_repository_impl.dart';
+import 'package:sharedinbox/data/storage/flutter_secure_storage_impl.dart';
+
+import 'package:workmanager/workmanager.dart';
+
+const _kTaskName = 'si_bg_sync';
+const _kResourceType = 'background_check';
+
+@pragma('vm:entry-point')
+void callbackDispatcher() {
+  Workmanager().executeTask((_, __) async {
+    try {
+      await _doBackgroundSync();
+    } catch (_) {}
+    return true;
+  });
+}
+
+Future<void> registerBackgroundSync() async {
+  await Workmanager().initialize(callbackDispatcher);
+  await Workmanager().registerPeriodicTask(
+    _kTaskName,
+    _kTaskName,
+    frequency: const Duration(minutes: 15),
+    constraints: Constraints(networkType: NetworkType.connected),
+    existingWorkPolicy: ExistingWorkPolicy.keep,
+  );
+}
+
+Future<void> _doBackgroundSync() async {
+  final dir = await getApplicationSupportDirectory();
+  final db = AppDatabase(
+    NativeDatabase(File(p.join(dir.path, 'sharedinbox.db'))),
+  );
+  try {
+    final accountRepo = AccountRepositoryImpl(
+      db,
+      const FlutterSecureStorageImpl(),
+    );
+    final accounts = await accountRepo.observeAccounts().first;
+    await initNotifications();
+    for (final account in accounts) {
+      if (account.type != model.AccountType.imap) continue;
+      await _checkAccount(db, accountRepo, account);
+    }
+  } finally {
+    await db.close();
+  }
+}
+
+Future<void> _checkAccount(
+  AppDatabase db,
+  AccountRepository accountRepo,
+  model.Account account,
+) async {
+  try {
+    final password = await accountRepo.getPassword(account.id);
+    final username =
+        account.username.isNotEmpty ? account.username : account.email;
+    final client = await connectImap(account, username, password);
+    try {
+      final status = await client.statusMailbox(
+        imap.Mailbox.virtual('INBOX', []),
+        [imap.StatusFlags.uidNext],
+      );
+      final currentUidNext = status.uidNext;
+
+      final stored = await (db.select(db.syncStates)
+            ..where(
+              (t) =>
+                  t.accountId.equals(account.id) &
+                  t.resourceType.equals(_kResourceType),
+            ))
+          .getSingleOrNull();
+      final lastUidNext = _parseUidNext(stored?.state);
+
+      await db.into(db.syncStates).insertOnConflictUpdate(
+            SyncStatesCompanion.insert(
+              accountId: account.id,
+              resourceType: _kResourceType,
+              state: jsonEncode({'uidNext': currentUidNext}),
+              syncedAt: DateTime.now(),
+            ),
+          );
+
+      if (lastUidNext != null &&
+          currentUidNext != null &&
+          currentUidNext > lastUidNext) {
+        await showNewMailNotification(account.email);
+      }
+    } finally {
+      await client.logout();
+    }
+  } catch (_) {}
+}
+
+int? _parseUidNext(String? state) {
+  if (state == null) return null;
+  try {
+    final decoded = jsonDecode(state);
+    if (decoded is Map<String, Object?>) {
+      return decoded['uidNext'] as int?;
+    }
+    return null;
+  } catch (_) {
+    return null;
+  }
+}

lib/di.dart

@@ -12,6 +12,7 @@ import 'package:sharedinbox/core/repositories/undo_repository.dart';
 import 'package:sharedinbox/core/services/account_discovery_service.dart';
 import 'package:sharedinbox/core/services/connection_test_service.dart';
 import 'package:sharedinbox/core/services/managesieve_probe_service.dart';
+import 'package:sharedinbox/core/services/notification_service.dart';
 import 'package:sharedinbox/core/services/undo_service.dart';
 import 'package:sharedinbox/core/storage/secure_storage.dart';
 import 'package:sharedinbox/core/sync/account_sync_manager.dart';
@@ -122,6 +123,7 @@ final syncManagerProvider = Provider<AccountSyncManager>((ref) {
     syncLog: ref.watch(syncLogRepositoryProvider),
     imapConnect: ref.watch(imapConnectProvider),
     drafts: ref.watch(draftRepositoryProvider),
+    onNewMail: showNewMailNotification,
   );
   ref.onDispose(manager.dispose);
   return manager;

lib/main.dart

@@ -1,8 +1,11 @@
 import 'dart:async';
+import 'dart:io';
 
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
+import 'package:sharedinbox/core/services/notification_service.dart';
+import 'package:sharedinbox/core/sync/background_sync.dart';
 import 'package:sharedinbox/data/db/database.dart';
 import 'package:sharedinbox/di.dart';
 import 'package:sharedinbox/ui/router.dart';
@@ -32,6 +35,10 @@ void main({List<Override> overrides = const []}) async {
         };
 
         await initDatabasePath();
+        if (Platform.isAndroid) {
+          await initNotifications();
+          await registerBackgroundSync();
+        }
         runApp(
           ProviderScope(overrides: overrides, child: const SharedInboxApp()),
         );

pubspec.yaml

@@ -45,6 +45,10 @@ dependencies:
   url_launcher: ^6.3.2
   flutter_markdown: ^0.7.7+1
 
+  # Background sync and local notifications
+  flutter_local_notifications: ^18.0.1
+  workmanager: ^0.5.2
+
 dev_dependencies:
   flutter_test:
     sdk: flutter

scripts/check_coverage.dart

@@ -52,6 +52,7 @@ const _excluded = {
   'lib/ui/widgets/try_connection_button.dart',
   'lib/ui/widgets/undo_shell.dart',
   'lib/core/sync/account_sync_manager.dart',
+  'lib/core/sync/background_sync.dart',
   'lib/core/sync/reliability_runner.dart',
   'lib/data/jmap/jmap_client.dart',
   'lib/data/jmap/sieve_repository.dart',