- execute-plan.md: Add checkpoint_return_for_orchestrator step
explaining how to return at checkpoints when spawned via Task tool
- subagent-task-prompt.md: Add checkpoint_behavior and completion_format
sections to guide agents on returning for checkpoints
Tested: Task resume works - agent pauses at checkpoint, returns with
details, orchestrator presents to user, resumes with Task(resume=id).
Parallel agents each get unique agent_id for independent resume.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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