Handle the parts of a plan that can't be decided by talking — answer every question the PRD, prompt, or codebase can already settle, then resolve what's genuinely unknowable with timeboxed probes and manipulable prototypes, gating progress on the user actually understanding what was decided. Keeps its map and findings on disk so an effort can span many context resets. Use this alongside or inside an interview-based planning skill such as plan-with-docs, whenever the user answers "I don't know yet", says a plan feels premature, says they need to prototype first, says they don't understand what the agent produced, or when the work is too big for one session. Also use it when a previous plan turned out to be wrong once building started, or to resume a fogged effort already underway.