feat: warn when server and client versions differ during connection setup

src/EchoHub.Client/AppOrchestrator.cs

@@ -1373,6 +1373,21 @@ public sealed class AppOrchestrator : IDisposable
                 _mainWindow.FocusInput();
                 FetchAndUpdateOnlineUsers();
             });
+
+            if (result.ServerInfo is not null && !string.IsNullOrEmpty(result.ServerInfo.Version)
+                && result.ServerInfo.Version != UpdateChecker.CurrentVersion)
+            {
+                InvokeUI(() => {
+                    var choice = MessageBox.Query(_app, "Version Mismatch",
+                    $"Server version {result.ServerInfo.Version} does not match client version {UpdateChecker.CurrentVersion}.\n\n" +
+                    "Some features may not work correctly. Consider updating both to the same version.",
+                    "Continue", "Disconnect");
+
+                    if (choice == 1)
+                        HandleDisconnect();
+                });
+            }
+
             SaveServerToConfig(dialogResult);
         }, "Connection failed", "Connect");
     }

src/EchoHub.Client/Services/ConnectionManager.cs

@@ -15,7 +15,8 @@ namespace EchoHub.Client.Services;
 internal record ConnectResult(
     LoginResponse Login,
     List<ChannelDto> Channels,
-    Dictionary<string, List<MessageDto>> Histories);
+    Dictionary<string, List<MessageDto>> Histories,
+    ServerStatusDto? ServerInfo = null);
 
 /// <summary>
 /// Owns connection lifecycle, authentication, SignalR event wiring, and channel tracking.
@@ -67,6 +68,17 @@ internal sealed class ConnectionManager : IAsyncDisposable
 
         try
         {
+            onStatus("Fetching server info...");
+            ServerStatusDto? serverInfo = null;
+            try
+            {
+                serverInfo = await _apiClient.GetServerInfoAsync();
+            }
+            catch (Exception ex)
+            {
+                Log.Warning(ex, "Failed to fetch server info");
+            }
+
             onStatus("Authenticating...");
 
             LoginResponse loginResponse;
@@ -165,7 +177,7 @@ internal sealed class ConnectionManager : IAsyncDisposable
             }
 
             onStatus("Connected");
-            return new ConnectResult(loginResponse, channels, histories);
+            return new ConnectResult(loginResponse, channels, histories, serverInfo);
         }
         catch
         {

src/EchoHub.Core/DTOs/ServerDtos.cs

@@ -5,6 +5,7 @@ public record ServerStatusDto(
     string? Description,
     int OnlineUsers,
     int TotalChannels,
-    string RegistrationMode = "open");
+    string RegistrationMode = "open",
+    string Version = "0.0.0");
 
 public record EncryptionKeyResponse(string Key);

src/EchoHub.Server/Controllers/ServerController.cs

@@ -1,3 +1,4 @@
+using System.Reflection;
 using System.Security.Claims;
 using EchoHub.Core.DTOs;
 using EchoHub.Core.Models;
@@ -38,12 +39,15 @@ public class ServerController : ControllerBase
             _ => "open",
         };
 
+        var version = typeof(ServerController).Assembly.GetName().Version?.ToString(3) ?? "0.0.0";
+
         var status = new ServerStatusDto(
             _config["Server:Name"] ?? "EchoHub Server",
             _config["Server:Description"],
             userCount,
             channelCount,
-            registrationMode);
+            registrationMode,
+            version);
 
         return Ok(status);
     }