Sessions: Sidebar, Session-Wechsel, Archivieren-Button, alles session-bezogen

Endpoints/ChatEndpoint.cs

@@ -50,16 +50,27 @@ public static class ChatEndpoint
         res.Headers["Cache-Control"] = "no-cache";
         res.Headers["Connection"] = "keep-alive";
 
+        var sessionId = body.SessionId;
+        if (string.IsNullOrEmpty(sessionId))
+        {
+            res.StatusCode = 400;
+            await res.WriteAsJsonAsync(new { error = "sessionId required" });
+            return;
+        }
+
         var chainId = Guid.NewGuid().ToString("N");
 
-        // Chain zuerst anlegen (FK für messages)
         await db.CreateChain(new ChainRecord
         {
             ChainId = chainId,
+            SessionId = sessionId,
             Model = modelId,
             SystemPrompt = body.SystemPrompt
         });
 
+        // Session-Timestamp aktualisieren
+        await db.UpdateSessionTimestamp(sessionId);
+
         var messages = new List<object>();
         foreach (var msg in body.Messages)
             messages.Add(new { role = msg.Role, content = msg.Content });