What problem does it solve? Removing old systems, APIs, and database columns is risky: hidden consumers depend on undocumented behavior, and in-place schema changes break rolling deploys. This Skill provides a disciplined process for deprecating code and migrating users and schemas without downtime. ## Core Features & Use Cases - Deprecation Decision Framework: Quantify consumer count, migration cost, and maintenance cost before deciding between advisory and compulsory deprecation. - Migration Patterns: Apply the Strangler pattern, Adapter pattern, and feature-flag cutovers to move consumers incrementally from old to new implementations. - Expand/Contract Schema Migrations: Rename or drop database columns in additive phases (expand, dual-write, backfill, contract) so old and new code stay valid at every deploy. - Use Case: You need to rename a name column to full_name in production. The Skill walks you through adding the nullable column, dual-writing, batch backfilling, switching reads, and dropping the old column in a separate deploy. ## Quick Start Ask the assistant to plan a deprecation and migration for your legacy service or to design an expand/contract migration for renaming a database column without downtime.
