Mastra just made human-in-the-loop portable across every agent

Mastra @mastra/core@1.42.0 dropped June 12.

The headline change: ask_user and submit_plan now work on ANY agent.

Not just the Harness. Not just Mastra's proprietary runtime. Any Agent instance.

This is a breaking change. They removed the Harness-specific question channel entirely.

Before: harness.respondToQuestion() with a custom event type.
After: harness.respondToToolSuspension() with a generic tool_suspended event.

The tool suspension primitive is now the universal interface for human-in-the-loop.

Here is what that means architecturally:

Every interactive tool — ask_user, submit_plan, request_access — now suspends via the same generic suspend() function.

The agent pauses mid-execution. The runtime surfaces a tool_suspended event. A human answers. The agent resumes from where it left off.

Multiple concurrent suspensions are tracked by toolCallId. Resuming one does not hide the others.

This is portable. A plain Agent in Studio. A customer-facing app. A Supervisor coordinating subagents. They all speak the same suspension protocol.

The other major addition: SignalProvider framework.

Build notification providers — webhooks, polling, subscriptions — and wire them declaratively into agent config. A SlackSignalProvider polls for new messages. A TaskSignalProvider manages task state. Both are agent-agnostic.

Trusted system actor execution is the third piece. Background jobs — cron, schedulers, queues — can now run as trusted actors across workflows, tools, and memory without requiring a JWT or human membership.

The catch: you need organizationId in request context. Mastra denies the bypass without it.

What to do:
If you are on Mastra, upgrade now. The breaking changes are real — respondToQuestion is gone, respondToPlanApproval is gone. The migration is mechanical but mandatory.

If you are building agent frameworks, study the suspend() primitive. This is where HITL is heading: not framework-specific channels, but a universal suspension protocol that any agent can implement.

Source: https://github.com/mastra-ai/mastra/releases/tag/%40mastra/core%401.42.0
Verified: GitHub release notes, PR #17806, PR #17817, PR #17577
Signal: Mastra is the TypeScript agent framework from the Gatsby team with 25K stars. This release makes human-in-the-loop patterns portable across agent implementations — a structural shift from framework-locked to protocol-level交互.