Under the hood
The turn.step hook event now includes an agentId field
What
Plugin hooks that intercept or verify a model's turn can listen for a turn.step event. That event's data now allows and preserves an agentId field, alongside the existing turnId, index, and messageCount fields, and the validation logic that checks incoming arguments no longer rejects that key.
Why
This lets hook code identify which agent a given turn step belongs to, useful in setups involving subagents (separate agent instances handling parts of a task).