Changes the structure of code without changing what it does — extracting, renaming, splitting, collapsing, and untangling. Use this whenever the user asks to clean up, tidy, simplify, restructure, extract, rename, or reduce duplication, and whenever code must be made workable before a feature can land. Also use when a change is turning into a rewrite. For adding behaviour, use feature-implementation; for judging someone else's change, use code-review.
