Recurrence Prevention (재발방지)

A defect that happens once is a bug. A defect that happens twice is a countermeasure failure — whatever was supposed to prevent the second occurrence (a mental note, a memory entry, a rule) demonstrably did not. So on a recurrence, the unit of work is not the fix (you already know the fix — you applied it last time). The unit of work is the countermeasure: re-evaluate the cause analysis and whatever was supposed to prevent this, repair or replace it, and reach for a more deterministic mechanism only when repairing the existing one cannot suffice. A recurrence is evidence for that re-evaluation, not an order to add a level.

This skill codifies a practice proven in the harness repo that ships it: the no-false-ship rule was created only after the third false-ship incident; CHANGELOG drift survived a written convention for seven releases and stopped only when a test gate enforced it; comment warnings against hardcoded-list drift failed twice before "derive to a single source" became mandatory. The pattern is consistent: each enforcement level fails in a characteristic way, and when one has demonstrably failed the answer is usually a more deterministic mechanism — not a louder version of the same level, and not a new mechanism when the existing one can be repaired.

When to use