Create a builtin story-executor agent with a tight system prompt for single-story execution, wire system/agent.requested to carry an optional agent name, make agent-dispatch use roster-based pi execution when present, switch trigger-prd story nodes to send agent=story-executor by default, harden the outer story wrapper with a pre-commit git-status guard, and update the operator docs/skill notes to match the new runtime contract.
Pi-subagent format: YAML frontmatter + markdown system prompt body.
Symlinked to .pi/agents/ for pi-subagent discovery.
Git-tracked in agents/ as lowest-priority builtin roster.