Overwrite

import { Annotation, StateGraph, Overwrite } from "@langchain/langgraph";

const State = Annotation.Root({
  messages: Annotation<string[]>({
    reducer: (a, b) => a.concat(b),
    default: () => [],
  }),
});

const replaceMessages = (_state: typeof State.State) => {
  return { messages: new Overwrite(["replacement"]) };
};