Refactor only what improves the current change

Name the pain: duplicated knowledge, confusing intent, difficult change, excessive coupling or an untestable boundary. Similar code with independent domain meanings need not be unified. Do not refactor solely to meet an invented line limit, layer count or pattern preference.

This skill changes structure and never behavior; a behavior change, even a small one, is tdd work with its own failing test. Find adequate existing behavioral tests. Without reliable coverage of the affected contract, go to legacy-code-change (characterize, cut the smallest seam) and return here afterwards. Distinguish observed legacy behavior from a known defect; do not freeze a defect as a desired contract. Keep intentional behavior changes separately understandable.

Prefer extract, rename, move or simplify over introducing a new engine or framework. Read references/REFACTORING_MOVES_REFERENCE.md for the concrete moves (preconditions, mechanics, verification) once the pain is named. Use an existing codemod where appropriate -- read references/AUTOMATED_REFACTORING_TOOLS.md for the tool catalog by language before hand-writing an AST transform -- inspect its scope and preserve unrelated WIP. Short green-to-green moves are compatible with a coherent final commit; do not create a PR per micro-edit unless the workflow requires it.

Test stability through change

Behavioral tests should continue to pass when only implementation changes. Remove coupling to private method names or call order unless the order itself is contractual. Do not add tests for renamed helpers just to replace deleted brittle ones. Retire a test only after its protection is preserved elsewhere, its behavior was removed or its assertion was shown not to protect a relevant requirement.

Rerun affected checks after the structural move and applicable final gates at integration. For the interface decision that precedes the move, use codebase-design; for choosing which checks must stay green while it happens, use layered-testing-executor.