Planning
A model-owned task list with the tools, texts and reminder of Pydantic AI Harness Planning: write_plan replaces the whole plan, read_plan shows ids, add_task, update_task_status, update_task_statuses (validated as a batch) and remove_task edit it. The current plan is appended to each turn as a <plan-reminder> (context), and every change is published to the UI as a data-plan part for the Plan element.