Implement a refactor

Restructure code so it reads, factors, or layers better — without moving any observable behavior. A refactor fails in exactly two ways: a behavior delta smuggled in under the "purely internal" label, and a compatibility shim that quietly becomes permanent. This guide adds the refactor discipline on top of the base implement-task rules. These are conventions the review packet inspects — nothing enforces them at edit time.

Plan the transformation first — the workspace's change plan covers baseline, waves, and rollback; this guide is the execution half. The defining test: if any observable behavior moves, the work is no longer a refactor — it is a rewrite (behavior changes on purpose) or a migration (API A → B). Stop and say so; do not proceed under the wrong label.

Rules