fix: ghost channel when trying to join a channel that doesn't exist

src/EchoHub.Client/Services/EchoHubConnection.cs

@@ -136,8 +136,10 @@ public sealed class EchoHubConnection : IAsyncDisposable
 
     public async Task<List<MessageDto>> JoinChannelAsync(string channelName)
     {
-        var messages = await _connection.InvokeAsync<List<MessageDto>>("JoinChannel", channelName);
-        return DecryptMessages(messages);
+        var result = await _connection.InvokeAsync<JoinChannelResult>("JoinChannel", channelName);
+        if (!result.Success)
+            throw new InvalidOperationException(result.Error ?? "Failed to join channel.");
+        return DecryptMessages(result.History);
     }
 
     public async Task LeaveChannelAsync(string channelName)

src/EchoHub.Core/DTOs/ChatDtos.cs

@@ -15,6 +15,8 @@ public record MessageDto(
     long? AttachmentFileSize = null,
     List<EmbedDto>? Embeds = null);
 
+public record JoinChannelResult(bool Success, List<MessageDto> History, string? Error = null);
+
 public record ChannelDto(
     Guid Id,
     string Name,

src/EchoHub.Server/Hubs/ChatHub.cs

@@ -56,7 +56,7 @@ public class ChatHub : Hub<IEchoHubClient>
         }
     }
 
-    public async Task<List<MessageDto>> JoinChannel(string channelName)
+    public async Task<JoinChannelResult> JoinChannel(string channelName)
     {
         try
         {
@@ -64,19 +64,15 @@ public class ChatHub : Hub<IEchoHubClient>
                 Context.ConnectionId, CurrentUserId, CurrentUsername, channelName);
 
             if (error is not null)
-            {
-                await Clients.Caller.Error(error);
-                return [];
-            }
+                return new JoinChannelResult(false, [], error);
 
             await Groups.AddToGroupAsync(Context.ConnectionId, channelName.ToLowerInvariant().Trim());
-            return history;
+            return new JoinChannelResult(true, history);
         }
         catch (Exception ex)
         {
             _logger.LogError(ex, "Error joining channel '{Channel}' for {User}", channelName, CurrentUsername);
-            await Clients.Caller.Error($"Failed to join channel: {ex.Message}");
-            return [];
+            return new JoinChannelResult(false, [], $"Failed to join channel: {ex.Message}");
         }
     }