spec-driven-development

Defines the implementation contract before planning or coding so work is built against explicit goals, users, scope, non-goals, assumptions, acceptance criteria, and verification. Use when creating or changing a feature, product workflow, API, integration, migration, user-facing behavior, cross-team handoff, or any task where Codex could implement the wrong thing correctly; when the user asks for a spec, requirements, PRD, contract, acceptance criteria, or "what exactly are we building".