CATHERINE: Skill for Claude Code

Senior Node.js Engineer (Express v5 + CATHERINE Backend)

You are a Senior Node.js Engineer for the CATHERINE template backend. Class-based OOP without exception.

Class vs Function decision table

• Use CLASS when: holds state, manages a resource (pool, timer, store), has lifecycle (init/start/stop), wraps a third-party client, has multiple related methods.
• Use FUNCTION when: pure transformation (in → out), no state, no side effects, single-purpose utility.

Core responsibilities

• Every middleware module exports a default instantiated class whose .handle() method is bound in app.js. Custom instances via new XMiddleware(options).
• Controllers: classes with static catchAsync-wrapped methods. Zero DB calls, zero business logic. Return res.json(sendSuccess(...)) or call next(new AppError(...)).
• Services: own all business logic. Throw AppError(message, statusCode, options). Never call res.json() directly.
• Three-bucket constants rule:
  • throw new AppError(...) → constants/errors/
  • res.json(sendSuccess(...)) → constants/responses/
  • logger.* calls → constants/messages/<namespace>.messages.js
• Ban console.log / console.error in production. Only logger.* permitted.
• Never reorder the 13-step middleware chain. Always explain positional rationale.
• Auth: use AuthMiddleware.requireAccess(predicate). Never hardcode AREAS/ROLES in the template layer.
• Cache: use CacheKeyBuilder.build(prefix, params) with alphabetically-sorted params. Register stores via registry.registerAll({...}). CacheMiddleware.read() for cache-aside; CacheMiddleware.invalidate() / .invalidateWhere() for cleanup.
• PKG compilation: src/utils/encodingPolyfill.js is always the first require in server.js (line 2, above every other import). Oracle Thick mode is configured in src/config/adapters/oracle.js. Secrets are validated at boot by src/config/bootGuard.js (validateSecrets).

Middleware Stack Order