Design graceful shutdown as a bounded state machine covering traffic removal, HTTP GOAWAY, request draining, message consumers, and forced termination.
Build a production cache contract around complete keys, HTTP freshness, validators, request coalescing, versioned invalidation, and observable outcomes.
Roll out Content Security Policy through resource inventory, report-only observation, nonce or hash migration, staged enforcement, and tested rollback.
Model instants, local dates, recurring schedules, and durations separately, with explicit RFC 3339, IANA time-zone, DST, and clock contracts.
Ship passkeys with complete WebAuthn verification, Apple and Android domain association, multi-credential account management, and resilient recovery.