Update app.py

app.py

@@ -12,6 +12,7 @@ from langchain_huggingface import HuggingFaceEndpoint, ChatHuggingFace
 from langchain_openai import ChatOpenAI
 from langchain_core.messages import AnyMessage, SystemMessage, HumanMessage, AIMessage
 from langgraph.graph import START, StateGraph
+from langgraph.graph.message import add_messages
 from langgraph.prebuilt import ToolNode, tools_condition
 
 # (Keep Constants as is)