Chesterton's Fence

Invoked whenever the agent is about to delete, refactor, modify, or "clean up" existing code that looks unused, redundant, mysterious, or "obviously wrong". The skill enforces an investigation protocol before any such change is committed. It produces:

1. A why-it-exists memo — the best available reconstruction of the code's purpose, drawn from history, tests, comments, and call-graph.
2. An edge-case checklist — what behaviours the existing code guarantees today, that any change must preserve (unless explicitly altering them).