Show replies inside nested threads on mobile

mobile/lib/features/channels/thread_detail_page.dart

@@ -53,9 +53,12 @@ class ThreadDetailPage extends HookConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
+    // The relay's thread query is root-scoped. Nested thread heads retain the
+    // original root ID, while top-level thread heads use their own ID.
+    final effectiveRootId = threadHead.rootId ?? threadHead.id;
     final repliesState = ref.watch(
       threadRepliesProvider(
-        ThreadRepliesArgs(channelId: channelId, rootId: threadHead.id),
+        ThreadRepliesArgs(channelId: channelId, rootId: effectiveRootId),
       ),
     );
     final replyMessages = repliesState.whenData((events) {
@@ -132,10 +135,6 @@ class ThreadDetailPage extends HookConsumerWidget {
     final liveHead =
         allMsgs.where((m) => m.id == threadHead.id).firstOrNull ?? threadHead;
 
-    // The root of the entire thread chain. If the current thread head is
-    // itself a root message its rootId is null, so fall back to its own id.
-    final effectiveRootId = threadHead.rootId ?? threadHead.id;
-
     // Channel names for message content rendering.
     final channelsAsync = ref.watch(channelsProvider);
     final channelNamesMap = <String, String>{};

mobile/test/features/channels/channel_detail_page_test.dart

@@ -142,6 +142,7 @@ Widget _buildTestable({
   ChannelActions Function(Ref ref)? createChannelActions,
   ReadStateNotifier? readStateNotifier,
   _FakeMessagesNotifier? messagesNotifier,
+  _NestedThreadRelaySession? relaySession,
   String? canvasContent,
   List<NostrEvent>? threadReplies,
 }) {
@@ -182,6 +183,8 @@ Widget _buildTestable({
         threadRepliesProvider(
           const ThreadRepliesArgs(channelId: _channelId, rootId: 'thread-root'),
         ).overrideWith((ref) async => threadReplies),
+      if (relaySession != null)
+        relaySessionProvider.overrideWith(() => relaySession),
       // Stub the relay client provider so preloadMembers doesn't crash.
       relayClientProvider.overrideWithValue(
         RelayClient(baseUrl: 'http://localhost:3000'),
@@ -1591,6 +1594,69 @@ void main() {
       expect(find.text(formatDayHeading(rootCreatedAt)), findsOneWidget);
       expect(find.text(formatDayHeading(nextDayCreatedAt)), findsOneWidget);
     });
+
+    testWidgets(
+      'nested thread queries the true root and renders its direct reply',
+      (tester) async {
+        final root = _textMsg(
+          id: 'root',
+          pubkey: 'alice',
+          content: 'Root message',
+          createdAt: 1000,
+        );
+        final nestedHead = _textMsg(
+          id: 'nested-head',
+          pubkey: 'bob',
+          content: 'Nested head',
+          createdAt: 1100,
+          extraTags: const [
+            ['e', 'root', '', 'root'],
+            ['e', 'root', '', 'reply'],
+          ],
+        );
+        final nestedReply = _textMsg(
+          id: 'nested-reply',
+          pubkey: 'carol',
+          content: 'Nested child',
+          createdAt: 1200,
+          extraTags: const [
+            ['e', 'root', '', 'root'],
+            ['e', 'nested-head', '', 'reply'],
+          ],
+        );
+        final relaySession = _NestedThreadRelaySession(
+          expectedRootId: root.id,
+          replies: [nestedHead, nestedReply],
+        );
+
+        await tester.pumpWidget(
+          _buildTestable(
+            messages: [root, nestedHead],
+            relaySession: relaySession,
+          ),
+        );
+        await tester.pumpAndSettle();
+
+        final threadMessages = formatTimeline([root, nestedHead]);
+        Navigator.of(tester.element(find.byType(ChannelDetailPage))).push(
+          MaterialPageRoute<void>(
+            builder: (_) => ThreadDetailPage(
+              threadHead: threadMessages.last,
+              allMessages: threadMessages,
+              channelId: _channelId,
+              currentPubkey: 'self',
+              isMember: true,
+              isArchived: false,
+            ),
+          ),
+        );
+        await tester.pumpAndSettle();
+
+        expect(relaySession.queryFilters, hasLength(1));
+        expect(relaySession.queryFilters.single.tags['#e'], [root.id]);
+        expect(findRichText('Nested child'), findsOneWidget);
+      },
+    );
   });
 }
 
@@ -1633,6 +1699,38 @@ class _ErrorMessagesNotifier extends ChannelMessagesNotifier {
       AsyncError('Connection failed', StackTrace.current);
 }
 
+class _NestedThreadRelaySession extends RelaySessionNotifier {
+  final String expectedRootId;
+  final List<NostrEvent> replies;
+  final List<NostrFilter> queryFilters = [];
+
+  _NestedThreadRelaySession({
+    required this.expectedRootId,
+    required this.replies,
+  });
+
+  @override
+  SessionState build() => const SessionState(status: SessionStatus.connected);
+
+  @override
+  Future<List<NostrEvent>> queryRelay(
+    List<NostrFilter> filters, {
+    Duration timeout = const Duration(seconds: 8),
+  }) async {
+    queryFilters.addAll(filters);
+    if (filters.single.tags['#e']?.single == expectedRootId) {
+      return replies;
+    }
+    return const [];
+  }
+
+  @override
+  Future<List<NostrEvent>> fetchHistory(
+    NostrFilter filter, {
+    Duration timeout = const Duration(seconds: 8),
+  }) async => const [];
+}
+
 class _FakeTypingNotifier extends ChannelTypingNotifier {
   final List<TypingEntry> _entries;
   _FakeTypingNotifier(this._entries) : super(_channelId);