DB: Message + Attachments in einer Transaktion speichern (1x fsync statt N+1)

Endpoints/ChatEndpoint.cs

@@ -133,28 +133,22 @@ public static class ChatEndpoint
             var attachmentInfos = lastUserMsg.GetAttachments();
             var attachmentBlocks = lastUserMsg.GetAttachmentBlocks();
 
-            var messageId = await db.SaveMessage(new MessageRecord
+            var attachmentRecords = attachmentBlocks.Select(b => new AttachmentRecord
+            {
+                Type = b.Type,
+                MediaType = b.MediaType,
+                FileName = b.FileName,
+                Data = b.Data
+            }).ToList();
+
+            await db.SaveMessageWithAttachments(new MessageRecord
             {
                 ChainId = chainId,
                 Iteration = 0,
                 Role = "user",
                 Type = "text",
-                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
-                });
-            }
+                Content = textContent
+            }, attachmentRecords);
         }
 
         var systemPrompt = new List<object>