Introducing Harness Channels

You can now run a multi-player harness from Slack, iMessage, WhatsApp, and Discord using Mastra Agent Controller chat channels. Every configured chat adapter acts as an interface, enabling multi-user prompting to drive a single session.

Each Agent Controller session coordinates the modes, models, storage, tool approvals, and subagents. Connected channels forward incoming messages to the session, while server- or client-side subscribers can passively observe or actively participate in conversations.

Before chat channels, Agent Controller sessions were single-user. Each session lived in a TUI or a UI that couldn't be shared. Now you can enable multi-user interactions on the chat platforms your team already use.

Get started

Install the Slack adapter:

npm install @chat-adapter/slack

Add createSlackAdapter() to your AgentController channels options. Setting toolDisplay: "card" renders approve and deny buttons in the Slack UI:

import { AgentController } from "@mastra/core/agent-controller";
import { createSlackAdapter } from "@chat-adapter/slack";
 
export const incidentController = new AgentController({
  id: "incident-controller",
  // ...
  channels: {
    adapters: {
      slack: {
        adapter: createSlackAdapter(),
        toolDisplay: "card"
      }
    },
    resolveResourceId: () => {
      return "incident-demo";
    }
  }
});

Subscribe to a session

Connect using the Mastra Client SDK. Pass the controller id and resourceId to subscribe to the session's event stream:

import { MastraClient } from "@mastra/client-js";
 
const client = new MastraClient({ baseUrl: "http://localhost:4111" });
const session = client.getAgentController("incident-controller").session("incident-demo");
 
await session.create();
 
const subscription = await session.subscribe({
  onEvent: (event) => {
    if (event.type === "message_update") {
      /* ... */
    }
    if (event.type === "tool_approval_required") {
      /* ... */
    }
  }
});

Send messages from a client

Use sendMessage() to post messages to the subscribed session:

await session.sendMessage("OK. Sally said we're good to roll back.");

For more information and full configuration options, see:

• Agent Controller
• Agent Controller - Chat channels
• Agent Controller reference
• Agent Controller - Session