Standards for writing scalable, performant, well-tested, production-grade code. Use whenever writing or reviewing implementation code in any language - functions, classes, modules, services, APIs - and whenever the user asks for tests, a refactor, a code review, error handling, performance work, or "make this production-ready". This is the default skill for any coding task that produces more than a throwaway snippet. Trigger it even if the user doesn't mention quality explicitly.
