lg_chat_agent.py

from llm import llm
from langgraph.graph import MessagesState, START, END, StateGraph
from langchain_core.messages import HumanMessage, AIMessage

def bot(state: MessagesState):
    user_message = state["messages"][-1].content

    response = llm.invoke(user_message)

    return {
        "messages": [AIMessage(content=response.content)]
    }

builder = StateGraph(MessagesState)

builder.add_node("bot", bot)
builder.add_edge(START, "bot")
builder.add_edge("bot", END)  # ✅ REQUIRED

graph = builder.compile()

def chat_response(user_message: str) -> str:
    result = graph.invoke(
        {"messages": [HumanMessage(content=user_message)]}
    )

    return result["messages"][-1].content