File-Upload: Attachments-Tabelle, Base64-Speicherung, Frontend mit Drag&Drop/Paste/Preview, Error-Handling Fix

Endpoints/ChatEndpoint.cs

@@ -104,20 +104,57 @@ public static class ChatEndpoint
 
         var messages = new List<object>();
         foreach (var msg in body.Messages)
-            messages.Add(new { role = msg.Role, content = msg.Content });
+        {
+            // Content bereinigen: interne Felder (_file_name) entfernen
+            JsonElement content = msg.Content;
+            if (msg.Content.ValueKind == System.Text.Json.JsonValueKind.Array)
+            {
+                var node = System.Text.Json.Nodes.JsonNode.Parse(msg.Content.GetRawText());
+                foreach (var block in node.AsArray())
+                {
+                    if (block is System.Text.Json.Nodes.JsonObject obj)
+                        obj.Remove("_file_name");
+                }
+                content = JsonSerializer.Deserialize<JsonElement>(node.ToJsonString());
+            }
+
+            messages.Add(new Dictionary<string, JsonElement>
+            {
+                ["role"] = JsonSerializer.Deserialize<JsonElement>($"\"{msg.Role}\""),
+                ["content"] = content
+            });
+        }
 
         // Nur die letzte User-Message speichern (= die neue)
         var lastUserMsg = body.Messages.LastOrDefault(m => m.Role == "user");
         if (lastUserMsg != null)
         {
-            await db.SaveMessage(new MessageRecord
+            var textContent = lastUserMsg.GetTextContent();
+            var attachmentInfos = lastUserMsg.GetAttachments();
+            var attachmentBlocks = lastUserMsg.GetAttachmentBlocks();
+
+            var messageId = await db.SaveMessage(new MessageRecord
             {
                 ChainId = chainId,
                 Iteration = 0,
                 Role = "user",
                 Type = "text",
-                Content = lastUserMsg.Content
+                Content = textContent,
+                AttachmentCount = attachmentBlocks.Count
             });
+
+            // Attachments separat speichern
+            foreach (var block in attachmentBlocks)
+            {
+                await db.SaveAttachment(new AttachmentRecord
+                {
+                    MessageId = messageId,
+                    Type = block.Type,
+                    MediaType = block.MediaType,
+                    FileName = block.FileName,
+                    Data = block.Data
+                });
+            }
         }
 
         var systemPrompt = new List<object>