Use .content (avoid TypeError)

graph.py

@@ -68,7 +68,7 @@ def normalize_messages(messages):
                 #tool_msg = messages[i]
                 #formatted_content = f"## Tool Call {count}\n\n{tool_msg.content}"
                 #tool_messages.append(formatted_content)
-                tool_messages.append(messages[i])
+                tool_messages.append(messages[i].content)
                 count += 1
                 i += 1