Introducing Harness Channels

You can now run a multi-player harness from Slack, iMessage, WhatsApp, and Discord using Mastra Agent Controller 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.