functional-designlisted

# Purpose Rewrite TypeScript business logic so it stops mutating its inputs: mutating functions become functions that return new values, hand-written loops become `.filter()`/`.map()`/`.reduce()` chains over named predicates, and interface properties gain `readonly`. Targets the main app's `src/lib/` services. This skill **edits files** and shows a before/after snippet per change. Done means: every refactored function is pure, immutable shapes carry `readonly`, and `npm run typecheck` passes. # Rules (never violate) 1. TypeScript only — never apply this to Python. 2. Edit only under `src/lib/`; a route handler gets at most one import-only Edit, never a refactor of its I/O. 3. Never wrap async I/O in a synchronous composition chain — `await`, then pipe the result through pure code. 4. Never introduce a new dependency (immer, ramda, lodash-fp) or an undeclared `pipe()`; chain methods or use sequential `const` assignments. 5. Verify every type by reading it — never guess a parameter shape. 6. Maximum 3 Edits per invocation, one per function, each with a shown diff. # Resources - Read `resources/refactor-procedure.md` before editing: the 7-step procedure, the route-handler boundary rule, the self-check, common mistakes, escalation triggers, two worked examples, and the failure-mode table. # How to use ## What it does Turns mutating, imperative business logic into pure functions over immutable data, applies the edits itself, and reports each change with the p