fix(mobile): handle rejected video preview authentication

Signed-off-by: Tom Brow <tomb@block.xyz>

mobile/lib/features/channels/message_content/video_preview.dart

@@ -30,8 +30,17 @@ final videoPreviewFrameLoaderProvider = Provider<VideoPreviewFrameLoader>((
   ref,
 ) {
   final auth = ref.watch(mediaGetAuthServiceProvider);
-  return (url) async =>
-      _loadVideoPreviewFrame(url, headers: await auth.headersForAsync(url));
+  return (url) async {
+    final Map<String, String> headers;
+    try {
+      headers = await auth.headersForAsync(url);
+    } catch (_) {
+      // Queue rejection or a failed signing worker leaves this preview
+      // unavailable. Do not attempt an unauthenticated video request.
+      return null;
+    }
+    return _loadVideoPreviewFrame(url, headers: headers);
+  };
 });
 
 class _MessageVideoPreview extends HookConsumerWidget {

mobile/test/features/channels/message_video_auth_test.dart

@@ -0,0 +1,59 @@
+import 'dart:isolate';
+
+import 'package:buzz/features/channels/message_content.dart';
+import 'package:buzz/shared/relay/media_auth.dart';
+import 'package:buzz/shared/theme/theme.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+
+class _FailingMediaAuth extends MediaGetAuthService {
+  _FailingMediaAuth(this.error)
+    : super(baseUrl: 'https://example.com', nsec: null);
+
+  final Object error;
+  final requests = <String>[];
+
+  @override
+  Future<Map<String, String>> headersForAsync(String url) async {
+    requests.add(url);
+    throw error;
+  }
+}
+
+void main() {
+  for (final failure in <String, Object>{
+    'queue overflow': StateError('Media authentication queue is full'),
+    'isolate startup': IsolateSpawnException('worker unavailable'),
+  }.entries) {
+    testWidgets('posterless video handles auth ${failure.key}', (tester) async {
+      const url = 'https://example.com/media/clip.mp4';
+      final auth = _FailingMediaAuth(failure.value);
+      await tester.pumpWidget(
+        ProviderScope(
+          overrides: [mediaGetAuthServiceProvider.overrideWithValue(auth)],
+          child: MaterialApp(
+            theme: AppTheme.light(),
+            home: const AppMarkdownTheme(
+              child: Scaffold(
+                body: MessageContent(
+                  content: '![video]($url)',
+                  tags: [
+                    ['imeta', 'url $url', 'm video/mp4'],
+                  ],
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+      await tester.pumpAndSettle();
+      expect(auth.requests, [url]);
+      expect(find.text('Video attachment'), findsOneWidget);
+      expect(tester.takeException(), isNull);
+      await tester.pumpWidget(const SizedBox.shrink());
+      await tester.pump();
+      expect(tester.takeException(), isNull);
+    });
+  }
+}