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name: refactoring description: Guide code refactoring using Martin Fowler's catalog of behavior-preserving transformations. Use during TDD REFACTOR phase, when code smells are detected (duplication, long methods, feature envy), when discussing structural improvements, or before behavioral changes (Tidy First).

Refactoring Skill

Apply behavior-preserving transformations to improve quality of any codes, including tests.

Core Principle

"Refactoring is a disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior." — Martin Fowler

Structural Changes Only

Allowed:

• Renaming for clarity
• Extracting functions/methods
• Removing duplication
• Simplifying expressions
• Moving files/modules between directories
• Reorganizing module boundaries

NOT allowed:

• Adding new functionality
• Fixing bugs (if you find one, write a failing test first)
• Changing observable behavior in any way

See library-application-criteria.md for public API constraints (libraries vs applications).

Refactoring Workflow

1. Ensure tests pass (you need a safety net)
2. Identify ONE smell to address
3. Choose appropriate pattern from patterns.md
4. Apply mechanically in small steps
5. Run tests after each step
6. Commit when green

Safety Rules

• Never refactor with failing tests
• One pattern at a time
• Commit after each successful refactor
• Revert immediately if tests fail