refactor

What problem does it solve? Code that works but is hard to read, poorly named, or cluttered with redundant defensive checks accumulates maintenance cost. This Skill improves the structure, naming, and documentation of code whose tests already pass, while guaranteeing behavior stays unchanged. ## Core Features & Use Cases - Behavior-Preserving Restructuring: Extract functions, reduce complexity, and apply design patterns while running tests continuously so nothing breaks. - Redundancy Removal with Provenance: Trace validate/assert/check helpers to their producers and remove only checks whose postconditions are proven by an exact cited test. - Naming and Documentation: Apply naming standards, add JSDoc with @example blocks, and write inline comments that explain why rather than what. - Use Case: A TypeScript module has grown past the project's max-lines threshold with duplicated guard checks after internal calls. Run the refactor skill on that area to split it via the Two-Stage Rule, remove proven-redundant checks, and document the public API. ## Quick Start Refactor the code in src/services/billing with focus on structure and redundancy, keeping all tests passing.