Selective listening

By default a participant reacts to external events from every other participant. To scope a participant so it only reacts to specific participant types, populate its listens list with those classes.

When listens is non-empty, the environment only delivers external events whose source is an instance of one of the listed classes:

import { BaseParticipant } from '@mozaik-ai/core';

export class Critic extends BaseParticipant {
  // Only react to events produced by Writer participants.
  protected listens = [Writer];
}

With the list above, the Critic receives onExternalModelMessage, onExternalFunctionCall, and the other onExternal* events only when the source is a Writer. Events from any other participant type are not delivered to it.

A few things to note:

• An empty listens (the default) means "listen to everyone".
• listens only scopes external events. A participant always receives its own events through the self handlers (onFunctionCall, onModelMessage, …).
• Messages and lifecycle hooks follow the same scoping: a scoped participant reacts to messages and membership changes from the types it listens to.

This is how you build focused collaborators — a reviewer that only watches writers, a guardrail that only watches tool-calling agents — without manual source instanceof checks inside every handler.