Express Middleware Feature Flag Checks — Auditable Node.js API Route Gating
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TL;DR: Put the feature-flag decision in server-side middleware, cache the result briefly, and record a compact decision event containing the flag key, outcome, request correlation ID, and policy version. For a gaming API, that is usually enough to explain why a premium route admitted or rejected a player without retaining every request body. Use is_enabled for a boolean gate and get_value when the flag carries a limit or variant. A browser flag is presentation, never entitlement. The dominant o