Answer one question that can't be settled by reading or arguing — build the smallest throwaway thing that makes the answer visible, inside a timebox, against a decision rule declared before the build starts. Returns a 4-line finding (Q / Tried / Found / Decides) plus a manipulable micro-world when the thing has a visible surface, then deletes the spike. Use when the user says "spike this", "try both and see", "we won't know until we build it", "is X fast enough", "which of A or B", "prototype it first", when an interview hits "I don't know yet" on something no one can know, or when `sightline` resolves a PROBE row. Standalone: /probe <question> [--rule "..."] [--box "..."].