fix basic agent

app.py

@@ -4,7 +4,7 @@ import requests
 import inspect
 import pandas as pd
 
-from langchain_core.messages import HumanMessage
+from langchain_core.messages import HumanMessage, AIMessage
 from agent import build_graph
 
 # (Keep Constants as is)
@@ -29,7 +29,8 @@ class BasicAgent:
             for msg in reversed(result["messages"]): # Look for the last AI message
                 # Check if the message is an AIMessage and has content
                 if isinstance(msg, AIMessage) and hasattr(msg, 'content') and msg.content:
-                    submitted_answer = msg.content
+                    # Convert content to string to ensure type consistency with return hint
+                    submitted_answer = str(msg.content)
                     break # Found the last AI message content
 
         return submitted_answer