Use when a decision would be settled faster by building something throwaway than by arguing about it - competing options that read identically once written down, a "show me a few versions before I commit" or "mock it up first", a state model or data shape that looks fine on paper and needs pushing through its awkward cases, a foundation choice with several viable shapes, or a grill question a fourth paraphrase has not moved. Not for choosing the aesthetic (/design-brief), writing the plan (/plan-grill), or building the real thing (/autonomous-loop).
