feat: sync guard - Blockieren alter Clients beim sync

LehrerApp.Desktop/Services/SyncAuthService.cs

@@ -1,11 +1,12 @@
 using System.Net;
 using System.Net.Http.Json;
+using LehrerApp.Sync;
 
 namespace LehrerApp.Desktop.Services;
 
 public class SyncAuthException(string userMessage) : Exception(userMessage);
 
-public enum SyncConnectionTestResult { Ok, Unauthorized, Unreachable }
+public enum SyncConnectionTestResult { Ok, Unauthorized, IncompatibleVersion, Unreachable }
 
 /// <summary>
 /// Login/Verbindungstest gegen den eigenen Sync-Server (LehrerApp.Api) — getrennt vom bereits
@@ -27,7 +28,10 @@ public class SyncAuthService(HttpClient http)
         HttpResponseMessage resp;
         try
         {
-            resp = await http.PostAsJsonAsync(CombineUrl(serverUrl, "/api/auth/login"), new { username, password });
+            using var req = SyncProtocol.CreateRequest(HttpMethod.Post,
+                CombineUrl(serverUrl, "/api/auth/login"));
+            req.Content = JsonContent.Create(new { username, password });
+            resp = await http.SendAsync(req);
         }
         catch (HttpRequestException)
         {
@@ -49,6 +53,7 @@ public class SyncAuthService(HttpClient http)
     public async Task<SyncConnectionTestResult> TestConnectionAsync(string serverUrl, string? token)
     {
         using var req = new HttpRequestMessage(HttpMethod.Get, CombineUrl(serverUrl, "/api/sync/status"));
+        req.Headers.Add(SyncProtocol.VersionHeaderName, SyncProtocol.CurrentVersion);
         if (token is not null)
             req.Headers.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", token);
 
@@ -56,6 +61,8 @@ public class SyncAuthService(HttpClient http)
         {
             var resp = await http.SendAsync(req);
             if (resp.StatusCode == HttpStatusCode.Unauthorized) return SyncConnectionTestResult.Unauthorized;
+            if (resp.StatusCode == HttpStatusCode.UpgradeRequired)
+                return SyncConnectionTestResult.IncompatibleVersion;
             return resp.IsSuccessStatusCode ? SyncConnectionTestResult.Ok : SyncConnectionTestResult.Unreachable;
         }
         catch (HttpRequestException) { return SyncConnectionTestResult.Unreachable; }