feat(langchain) new middleware concept for createAgent

[christian-bromann]

We want to introduce a new middleware concept that allows user to create various middlewares for createAgent.

Requirements

We expect a middleware to:

• contain the following properties:

  • name - for logging and introspection

  • stateSchema - defines a specification for state updates

  • contextSchema - defines a specification for context

  • beforeModel - runs before the model is invoked, allows to update state or use controls

    (property) beforeModel?: (
      state: TState,
      runtime: Runtime<TState>,
      controls: Controls<TState>
    ) => MiddlewareResult<TState> | Promise<MiddlewareResult<TState>>

  • prepareModelRequest - runs before the model is invoked, allows to update model call parameters

    (property) prepareModelRequest?: (
      options: ModelRequest,
      state: TState,
      runtime: Runtime<TState>
    ) => Promise<PreparedCall | undefined> | PreparedCall | undefined;

  • afterModel - runs after the model is invoked, allows to update state or use controls

    (property) afterModel?: (
      state: TState,
      runtime: Runtime<TState>,
      controls: Controls<TState>
    ) => MiddlewareResult<TState> | Promise<MiddlewareResult<TState>>

• have access to state: an objects that holds information that persists across multiple invocations and is a union of the middlewares defined stateSchema and a built-in schema, e.g. currently only containing messages

• have access to runtime: an object that holds readonly information containing context data and other useful meta information useful for a specific invocation

• Any errors thrown within prepareCall or beforeModel and afterModel should bubble up

For more documentation, please refer to: https://docs.langchain.com/oss/javascript/langchain-middleware

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