Use when implementing any feature, service, or multi-step coding task, before writing any code — including when the user asks for incremental delivery, small PRs, reviewable chunks, or "build X". Delivers work as a sequence of stages each opened by one failing acceptance test, with a test suite that only ever tightens, halting for human review at every stage boundary. If there is even a 1% chance a coding task spans more than one edit, use this skill.
