What problem does it solve? Codebases that deliberately favor parallel copies over shared abstractions accumulate duplicated decisions—re-listed unions, copied helpers, prose restating code facts—that can drift apart silently. This Skill provides the classification rubric, authoring rules, and five-pass audit method to find, classify, and prevent such drift before it becomes a live bug. ## Core Features & Use Cases - Classification rubric: Assigns every duplicated pair a verdict—guarded, benign parallel, drift-prone, or diverged—based on whether copies must agree and what mechanically checks them. - Authoring rules: Six prevention rules covering deriving from authorities, registering or testing intentional copies, completeness checks for union membership, exhaustive vs. partial switches, and prose that restates code. - Five-pass audit method: A structured sweep covering cross-surface wiring, literals and unions, prose parity claims, derived artifacts, and structural clones, seeded by the deterministic npm run audit:duplication detector. - Use Case: When reviewing a diff that adds a second copy of a decision (e.g., a z.enum restating a core union in both CLI and MCP surfaces), apply the rubric to decide whether it needs a drift test, a parity manifest entry, or derivation from a shared authority. ## Quick Start Audit this repository for duplicated decisions that must agree but have no mechanical check, and classify each finding using the drift rubric.
