Use when the user wants to: design/redesign modules and layers, choose between a library and own code, understand why a project became a god-file, add an abstraction "for growth," update a DB schema without data loss, or during architecture review. Covers: YAGNI until second need, stdlib-first, modules by change reason, shared core + thin adapters, config outside repo + defaults in code, schema evolution without DROP, provider fallback chain, non-representable invalid states, dead code removal. Do not use for money (money-path-safety), hardening (hardening-observability), or refactoring (agent-refactor-safety).
