Building a Node.js Feature Flag Service with Deterministic Rollbacks

A short guide proposes building a small Node.js feature flag service around versioned, immutable flag snapshots and deterministic evaluation. Each game AI turn should emit one structured decision record that identifies the flag, cohort, configuration version, result, and evaluation time. The author recommends failing closed for risky behavior and caching the last known-good document so that rollback is a single version change. Unknown keys and malformed audience rules should be rejected at publish time rather than at request time. The design keeps evaluation separate from the HTTP handler, so it can be unit-tested without a running server.