[langgraph]: Quickstart guide, name mismatch in MessagesState and the returned value in llm_call function

[ybillwang]

Type of issue

issue / bug

Language

Python

Description

In langgraph quickstart page, there is a mismatch of MessagesState definition and the llm_call return value.

I think model_calls in MessagesState should be changed to llm_calls, to match the return dict in llm_call.

[ybillwang]

#1046 has been created.