Update app.py

app.py

@@ -2,7 +2,11 @@ from langchain_openai import OpenAIEmbeddings
 from langchain_community.vectorstores import Chroma
 from langchain_core.messages import HumanMessage, AIMessage
 from langchain_text_splitters import RecursiveCharacterTextSplitter
-from langgraph.graph import StateGraph, END, START
+from langgraph.graph import StateGraph  # Only import StateGraph from here
+# Define START and END manually
+START = "__start__"
+END = "__end__"
+
 from langgraph.prebuilt import ToolNode
 from langgraph.graph.message import add_messages
 from typing_extensions import TypedDict, Annotated