feat: implement channel membership management and ensure default channels are public

src/EchoHub.Client/AppOrchestrator.cs

@@ -712,12 +712,10 @@ public sealed class AppOrchestrator : IDisposable
             _joinedChannels.Add(channel.Name);
             var history = await _connection!.JoinChannelAsync(channel.Name);
 
-            // Refresh the channel list and ensure private channels show up
-            var channels = await _apiClient.GetChannelsAsync();
             InvokeUI(() =>
             {
-                _mainWindow.SetChannels(channels);
                 _mainWindow.EnsureChannelInList(channel.Name);
+                _mainWindow.SetChannelTopic(channel.Name, channel.Topic);
                 _mainWindow.SwitchToChannel(channel.Name);
                 if (history.Count > 0)
                     _mainWindow.LoadHistory(channel.Name, history);
@@ -756,10 +754,9 @@ public sealed class AppOrchestrator : IDisposable
             await _apiClient!.DeleteChannelAsync(channel);
             _joinedChannels.Remove(channel);
 
-            var channels = await _apiClient.GetChannelsAsync();
             InvokeUI(() =>
             {
-                _mainWindow.SetChannels(channels);
+                _mainWindow.RemoveChannel(channel);
                 _mainWindow.SwitchToChannel(HubConstants.DefaultChannel);
                 _mainWindow.AddSystemMessage(HubConstants.DefaultChannel, $"Channel #{channel} has been deleted.");
             });
@@ -844,6 +841,16 @@ public sealed class AppOrchestrator : IDisposable
             });
         };
 
+        connection.OnChannelUpdated += channel =>
+        {
+            InvokeUI(() =>
+            {
+                if (channel.IsPublic)
+                    _mainWindow.EnsureChannelInList(channel.Name);
+                _mainWindow.SetChannelTopic(channel.Name, channel.Topic);
+            });
+        };
+
         connection.OnError += errorMessage =>
             InvokeUI(() => _mainWindow.ShowError(errorMessage));
 

src/EchoHub.Client/UI/MainWindow.cs

@@ -596,6 +596,16 @@ public sealed class MainWindow : Runnable
         RefreshChannelList();
     }
 
+    /// <summary>
+    /// Remove a channel from the left panel list.
+    /// </summary>
+    public void RemoveChannel(string channelName)
+    {
+        _channelNames.Remove(channelName);
+        _channelTopics.Remove(channelName);
+        RefreshChannelList();
+    }
+
     /// <summary>
     /// Update the topic for a specific channel.
     /// </summary>