feat(extensions): manual verification help when browser launch fails

Expose a root navigator for global dialogs, show a fallback help sheet
with copy and reopen actions when verification URLs cannot launch, and
schedule the same prompt after a timeout during pending grants.

lib/utils/extension_auth_launcher.dart

@@ -1,3 +1,9 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:spotiflac_android/l10n/l10n.dart';
+import 'package:spotiflac_android/services/app_navigation_service.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';
 import 'package:spotiflac_android/utils/logger.dart';
 import 'package:url_launcher/url_launcher.dart';
@@ -30,6 +36,7 @@ bool _containsHttpStatusCode(String message, String code) {
 Future<bool> openPendingExtensionVerification(
   String extensionId, {
   String browserMode = 'external_first',
+  void Function(Uri authUri)? onAuthUri,
 }) async {
   final normalizedExtensionId = extensionId.trim();
   if (normalizedExtensionId.isEmpty) return false;
@@ -43,19 +50,9 @@ Future<bool> openPendingExtensionVerification(
 
     final uri = Uri.tryParse(authUrl);
     if (uri == null) return false;
+    onAuthUri?.call(uri);
 
-    final preferInApp = browserMode.trim().toLowerCase() == 'in_app_first';
-    final firstMode = preferInApp
-        ? LaunchMode.inAppBrowserView
-        : LaunchMode.externalApplication;
-    final fallbackMode = preferInApp
-        ? LaunchMode.externalApplication
-        : LaunchMode.inAppBrowserView;
-
-    var launched = await launchUrl(uri, mode: firstMode);
-    if (!launched) {
-      launched = await launchUrl(uri, mode: fallbackMode);
-    }
+    final launched = await _launchVerificationUrl(uri, browserMode);
 
     if (launched) {
       _log.i('Opened verification challenge for $normalizedExtensionId');
@@ -63,6 +60,12 @@ Future<bool> openPendingExtensionVerification(
       _log.w(
         'Could not open verification challenge for $normalizedExtensionId',
       );
+      return showExtensionVerificationHelpDialog(
+        normalizedExtensionId,
+        uri,
+        browserMode: browserMode,
+        immediateFailure: true,
+      );
     }
     return launched;
   } catch (e) {
@@ -72,3 +75,119 @@ Future<bool> openPendingExtensionVerification(
     return false;
   }
 }
+
+Timer? scheduleExtensionVerificationHelpDialog(
+  String extensionId,
+  Uri? authUri, {
+  String browserMode = 'external_first',
+  Duration delay = const Duration(seconds: 20),
+}) {
+  final normalizedExtensionId = extensionId.trim();
+  if (normalizedExtensionId.isEmpty || authUri == null) return null;
+
+  return Timer(delay, () {
+    unawaited(
+      showExtensionVerificationHelpDialog(
+        normalizedExtensionId,
+        authUri,
+        browserMode: browserMode,
+      ),
+    );
+  });
+}
+
+Future<bool> showExtensionVerificationHelpDialog(
+  String extensionId,
+  Uri authUri, {
+  String browserMode = 'external_first',
+  bool immediateFailure = false,
+}) async {
+  final context = AppNavigationService.rootNavigatorKey.currentContext;
+  if (context == null) {
+    _log.w('Cannot show verification help dialog without root context');
+    return false;
+  }
+
+  final l10n = context.l10n;
+  final title = immediateFailure
+      ? l10n.extensionVerificationHelpTitleManual
+      : l10n.extensionVerificationHelpTitleWaiting;
+  final message = immediateFailure
+      ? l10n.extensionVerificationHelpMessageManual
+      : l10n.extensionVerificationHelpMessageWaiting;
+
+  await showDialog<void>(
+    context: context,
+    useRootNavigator: true,
+    builder: (dialogContext) {
+      final dialogL10n = dialogContext.l10n;
+      return AlertDialog(
+        title: Text(title),
+        content: Column(
+          mainAxisSize: MainAxisSize.min,
+          crossAxisAlignment: CrossAxisAlignment.stretch,
+          children: [
+            Text(message),
+            const SizedBox(height: 16),
+            DecoratedBox(
+              decoration: BoxDecoration(
+                color: Theme.of(dialogContext).colorScheme.surfaceContainerHigh,
+                borderRadius: BorderRadius.circular(8),
+              ),
+              child: Padding(
+                padding: const EdgeInsets.all(12),
+                child: SelectableText(
+                  authUri.toString(),
+                  maxLines: 4,
+                  minLines: 1,
+                ),
+              ),
+            ),
+          ],
+        ),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.of(dialogContext).pop(),
+            child: Text(dialogL10n.extensionVerificationClose),
+          ),
+          TextButton.icon(
+            icon: const Icon(Icons.copy),
+            label: Text(dialogL10n.extensionVerificationCopyLink),
+            onPressed: () {
+              Clipboard.setData(ClipboardData(text: authUri.toString()));
+              ScaffoldMessenger.maybeOf(dialogContext)?.showSnackBar(
+                SnackBar(
+                  content: Text(dialogL10n.extensionVerificationLinkCopied),
+                ),
+              );
+            },
+          ),
+          FilledButton.icon(
+            icon: const Icon(Icons.open_in_browser),
+            label: Text(dialogL10n.extensionVerificationOpenBrowser),
+            onPressed: () {
+              unawaited(_launchVerificationUrl(authUri, browserMode));
+            },
+          ),
+        ],
+      );
+    },
+  );
+  return true;
+}
+
+Future<bool> _launchVerificationUrl(Uri uri, String browserMode) async {
+  final preferInApp = browserMode.trim().toLowerCase() == 'in_app_first';
+  final firstMode = preferInApp
+      ? LaunchMode.inAppBrowserView
+      : LaunchMode.externalApplication;
+  final fallbackMode = preferInApp
+      ? LaunchMode.externalApplication
+      : LaunchMode.inAppBrowserView;
+
+  var launched = await launchUrl(uri, mode: firstMode);
+  if (!launched) {
+    launched = await launchUrl(uri, mode: fallbackMode);
+  }
+  return launched;
+}