API Versioning Without the Mess

Deep dive into practical API versioning strategies beyond the usual REST basics — comparing URL-path versioning, custom header negotiation (Accept-Versioned), and query param approaches with concrete tradeoffs. Then build out a lightweight API gateway pattern using Ktor or Express that routes requests to versioned handler chains, supports sunset headers for deprecation signaling, and uses OpenAPI spec diffing in CI to catch accidental breaking changes before they ship. Include real schema evolution examples (field renames, type changes, nested object restructuring) and the adapter/transformer layer that keeps your internal domain models clean while supporting 3+ API versions simultaneously.