Drives iterative development of the Pet Central trusted marketplace. Use when building features, improving UI/UX, implementing backend modules, testing, or completing any work described in docs/spec.md. Applies to all apps (web-consumer, web-vendor, web-admin, web-partner, web-kiosk), packages (ui, database, auth, etc.), and the api-gateway. Includes complete testing and validation with correction loops until the system is fully functional.