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.

When NOT to use

• The behavior is correct but slow → hotpath.
• The fix is known and documented → scout confirms, then just fix it.
• The user wants tests around known-good behavior → proof.

Workflow

1. Reproduce