Antifailure sells a disposable production twin per pull request, including a firewall that fakes Stripe and SendGrid.

Four components: an Isolated Twin destroyed after the test, Safe State (sanitized, referentially consistent, production-shaped Postgres), a Side-Effect Firewall simulating external APIs instead of calling them, and Load, which replays production traffic patterns from access logs (Antifailure). It targets the gap where neither Vercel-style previews nor Neon-style database branching gives you real traffic or safe external calls. The side-effect firewall is the piece nobody else packages, and it's the reason most teams never test migrations against real data.