fix(llc, core): port e2e-suite thread fix and disposed-channel sort crash to v9

packages/stream_chat/CHANGELOG.md

@@ -8,6 +8,7 @@
 
 - Fixed `StreamChatClient.sync` letting a failure from its final `updateLastSyncAt` write escape to the caller; it is now handled by the method's own error handling, like every other sync failure.
 - Fixed `ChannelClientState` no longer handling `notification.mark_read` (regression since 9.20.0), which left `unreadCount` stale after `Channel.markRead` on channels the user isn't watching.
+- Fixed `Channel.getReplies` adding the parent message to `ChannelClientState.threads` when a backend returns it alongside the replies, which rendered the thread root twice. The online path now filters it out, matching the offline one.
 
 ## 9.27.0
 

packages/stream_chat/lib/src/client/channel.dart

@@ -3480,15 +3480,17 @@ class ChannelClientState {
     List<Message> messages, {
     bool upsert = true,
   }) {
-    var messagesToMerge = messages;
+    // The parent is rendered in its own slot, so keep it out of the reply list
+    // even when a backend returns it alongside the replies.
+    var messagesToMerge = messages.where((it) => it.id != parentId).toList();
     if (!upsert) {
       final existingThread = threads[parentId];
       // Don't create a phantom entry for a thread that was never paged in,
       // and only update replies already loaded in it.
       if (existingThread == null) return;
       final existingIds = {for (final m in existingThread) m.id};
       messagesToMerge =
-          messages.where((m) => existingIds.contains(m.id)).toList();
+          messagesToMerge.where((m) => existingIds.contains(m.id)).toList();
       if (messagesToMerge.isEmpty) return;
     }
 

packages/stream_chat/test/src/client/channel_test.dart

@@ -3112,6 +3112,32 @@ void main() {
       verify(() => client.getReplies(parentId)).called(1);
     });
 
+    test('`.getReplies` keeps the parent message out of the thread', () async {
+      const parentId = 'test-parent-id';
+
+      // Some backends return the parent as the first message of the oldest
+      // page. It is rendered from its own copy, so it must not also become a
+      // reply — otherwise the thread shows its root twice.
+      final messages = [
+        Message(id: parentId),
+        ...List.generate(
+          3,
+          (index) => Message(id: 'test-message-id-$index', parentId: parentId),
+        ),
+      ];
+
+      when(() => client.getReplies(parentId)).thenAnswer(
+        (_) async => QueryRepliesResponse()..messages = messages,
+      );
+
+      await channel.getReplies(parentId);
+
+      final threadMessages = channel.state!.threads[parentId];
+      expect(threadMessages, isNotNull);
+      expect(threadMessages!.length, messages.length - 1);
+      expect(threadMessages.any((it) => it.id == parentId), isFalse);
+    });
+
     test('`.getReactions`', () async {
       const messageId = 'test-message-id';
 

packages/stream_chat_flutter_core/CHANGELOG.md

@@ -1,3 +1,9 @@
+## Upcoming
+
+🐞 Fixed
+
+- Fixed `StreamChannelListController` crashing with a null-check error when its local sort ran over a channel disposed mid-query (e.g. a client disconnect/logout racing an in-flight `loadMore`); such channels are now sorted last instead.
+
 ## 9.27.0
 
 ✅ Added

packages/stream_chat_flutter_core/lib/src/stream_channel_list_controller.dart

@@ -155,8 +155,17 @@ class StreamChannelListController extends PagedValueNotifier<int, Channel> {
           orElse: () => newValue,
           (success) => success.copyWith(
             items: success.items.sortedByCompare(
-              (it) => it.state!.channelState,
-              channelSort.compare,
+              // A channel loses its state when it is disposed — e.g. a client
+              // disconnect/logout or a channel-removal event racing an
+              // in-flight query — so sort stateless channels last instead of
+              // null-asserting on them.
+              (it) => it.state?.channelState,
+              (a, b) => switch ((a, b)) {
+                (null, null) => 0,
+                (null, _) => 1,
+                (_, null) => -1,
+                (final a?, final b?) => channelSort.compare(a, b),
+              },
             ),
           ),
         ),

packages/stream_chat_flutter_core/test/stream_channel_list_controller_test.dart

@@ -285,6 +285,41 @@ void main() {
     },
   );
 
+  test(
+      'local sort places channels with disposed state last instead of crashing',
+      () {
+    ChannelState channelStateFor({required DateTime createdAt}) => ChannelState(
+          channel: ChannelModel(
+            cid: 'messaging:${createdAt.millisecondsSinceEpoch}',
+            createdAt: createdAt,
+          ),
+        );
+
+    final older = MockChannel();
+    when(() => older.state.channelState)
+        .thenReturn(channelStateFor(createdAt: DateTime(2026, 1, 1)));
+
+    final newer = MockChannel();
+    when(() => newer.state.channelState)
+        .thenReturn(channelStateFor(createdAt: DateTime(2026, 6, 1)));
+
+    // A channel disposed while a query is in flight (client disconnect or
+    // logout, a channel-removal event) has its state nulled out.
+    final disposed = NonInitializedMockChannel();
+
+    final controller = StreamChannelListController(
+      client: client,
+      channelStateSort: defaultChannelListSort,
+    );
+
+    expect(
+      () => controller.value =
+          PagedValue<int, Channel>(items: [disposed, older, newer]),
+      returnsNormally,
+    );
+    expect(controller.value.asSuccess.items, equals([newer, older, disposed]));
+  });
+
   group('Event handling', () {
     late StreamController<Event> eventController;