fix: upgrade workmanager 0.5.2 → 0.9.0+3 to fix Kotlin 2.x compile error

workmanager 0.5.2 references the removed PluginRegistrantCallback and
other V1 Flutter embedding APIs, causing a Kotlin compilation failure
when building the release AAB with AGP 8.11.1 / Kotlin 2.2.20.

0.9.x uses only V2 embedding. API migration: ExistingWorkPolicy →
ExistingPeriodicWorkPolicy for registerPeriodicTask.

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

android/app/build.gradle.kts

@@ -13,6 +13,7 @@ android {
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_17
         targetCompatibility = JavaVersion.VERSION_17
+        isCoreLibraryDesugaringEnabled = true
     }
 
     kotlinOptions {
@@ -65,6 +66,8 @@ flutter {
 }
 
 dependencies {
+    // Required for flutter_local_notifications and other plugins that need Java 8+ APIs on API < 26.
+    coreLibraryDesugaring("com.android.tools:desugar_jdk_libs:2.1.4")
     // integration_test is a dev dependency; the Flutter plugin loader adds it as
     // debugImplementation only, but GeneratedPluginRegistrant.java (in src/main)
     // references its class in all variants. Make it available for release compilation

lib/core/sync/background_sync.dart

@@ -38,7 +38,7 @@ Future<void> registerBackgroundSync() async {
     _kTaskName,
     frequency: const Duration(minutes: 15),
     constraints: Constraints(networkType: NetworkType.connected),
-    existingWorkPolicy: ExistingWorkPolicy.keep,
+    existingWorkPolicy: ExistingPeriodicWorkPolicy.keep,
   );
 }
 

lib/ui/screens/email_detail_screen.dart

@@ -186,7 +186,7 @@ class _EmailDetailScreenState extends ConsumerState<EmailDetailScreen> {
                 ),
               ),
             ),
-          Html(
+          _SafeHtml(
             data: body.htmlBody!,
             extensions: [if (!_loadRemoteImages) _BlockRemoteImagesExtension()],
           ),
@@ -501,6 +501,57 @@ class _UnsubscribeChip extends StatelessWidget {
   }
 }
 
+/// Renders [Html] and falls back to an error message if the widget throws
+/// during build, preventing a malformed body from crashing the whole screen.
+class _SafeHtml extends StatefulWidget {
+  const _SafeHtml({required this.data, required this.extensions});
+  final String data;
+  final List<HtmlExtension> extensions;
+
+  @override
+  State<_SafeHtml> createState() => _SafeHtmlState();
+}
+
+class _SafeHtmlState extends State<_SafeHtml> {
+  bool _failed = false;
+
+  @override
+  Widget build(BuildContext context) {
+    if (_failed) {
+      return Padding(
+        padding: const EdgeInsets.all(8),
+        child: Row(
+          children: [
+            Icon(
+              Icons.warning_amber_outlined,
+              color: Theme.of(context).colorScheme.error,
+              size: 16,
+            ),
+            const SizedBox(width: 8),
+            const Expanded(child: Text('Message body could not be rendered.')),
+          ],
+        ),
+      );
+    }
+
+    // Intercept any build-phase throw from flutter_html for this subtree.
+    // We save/restore via postFrameCallback so other widgets are unaffected.
+    final prev = ErrorWidget.builder;
+    ErrorWidget.builder = (FlutterErrorDetails details) {
+      ErrorWidget.builder = prev;
+      WidgetsBinding.instance.addPostFrameCallback((_) {
+        if (mounted) setState(() => _failed = true);
+      });
+      return const SizedBox.shrink();
+    };
+    WidgetsBinding.instance.addPostFrameCallback(
+      (_) => ErrorWidget.builder = prev,
+    );
+
+    return Html(data: widget.data, extensions: widget.extensions);
+  }
+}
+
 class _BlockRemoteImagesExtension extends HtmlExtension {
   @override
   Set<String> get supportedTags => {'img'};

pubspec.yaml

@@ -47,7 +47,7 @@ dependencies:
 
   # Background sync and local notifications
   flutter_local_notifications: ^18.0.1
-  workmanager: ^0.5.2
+  workmanager: ^0.9.0
 
 dev_dependencies:
   flutter_test: