sleuth: find the cause, not a place to type

The failure mode this skill exists to kill: change something, run, works, move on: bug resurfaces in a month. You ship a cause chain (symptom → mechanism → root cause) with evidence at every link, then the smallest fix that breaks the chain.

Purpose, authority, and safety

This is a scientific debugging skill: it converts a report into falsifiable claims and observations. It is not permission to experiment recklessly in production. Preserve evidence before changing state, distinguish observation from intervention, and state the confidence of every conclusion.