deprecation-and-migration

Treats code as a liability and walks through deprecation/migration end-to-end: when to maintain vs sunset (decision questions), advisory vs compulsory deprecation, the migration process (build replacement → announce/document → migrate consumers incrementally → remove old system), and patterns like Strangler, Adapter, and feature-flag migration. Calls out Hyrum's Law, the Churn Rule, zombie code, and common rationalizations to push back on.