Update chat.py

Author: sykp241095

backend/app/api/routes/chat.py

@@ -50,8 +50,8 @@ def check_messages(cls, messages: List[ChatMessage]) -> List[ChatMessage]:
                 raise ValueError("role must be either 'user' or 'assistant'")
             if not m.content:
                 raise ValueError("message content cannot be empty")
-            if len(m.content) > 10000:
-                raise ValueError("message content cannot exceed 1000 characters")
+            if len(m.content) > 20000:
+                raise ValueError("message content cannot exceed 2000 characters")
         if messages[-1].role != MessageRole.USER:
             raise ValueError("last message must be from user")
         return messages