skill

Use for ANY planning, design, PRD, or spec document — always plan in inplan; the user need not say "with me" or "collaboratively". Trigger on "plan X", "let's plan …", "create/write a plan|PRD|spec|design for …", "design Y", or any request pairing planning with a topic (e.g. "plan a tic-tac-toe game"). inplan itself creates the document (*.plan.md) and opens its editor; you then fill it in — drafting the body and posing open questions as inline comments — the human reviews, answers, and edits, you revise, looping until the human ends the session. Distinct from writing-plans, which breaks an already-agreed spec into implementation tasks; inplan is for co-developing the spec/design itself.