fix(langgraph): include the payload with the original user message that is going to be regenerated

Author: ranst91

typescript-sdk/integrations/langgraph/python/ag_ui_langgraph/agent.py

@@ -688,8 +688,11 @@ async def get_checkpoint_before_message(self, message_id: str, thread_id: str):
 
                 snapshot_values_without_messages = snapshot.values.copy()
                 del snapshot_values_without_messages["messages"]
-                checkpoint = history_list[idx - 1] # use one snapshot *before* the one that includes the message
-                checkpoint.values = {**checkpoint.values, **snapshot_values_without_messages}
+                checkpoint = history_list[idx - 1]
+
+                merged_values = {**checkpoint.values, **snapshot_values_without_messages}
+                checkpoint = checkpoint._replace(values=merged_values)
+
                 return checkpoint
 
         raise ValueError("Message ID not found in history")