Canary Deployment

1. The Incident

Version 1.43 did everything right by the last lesson's book: deployed to green, health-gated, smoke-tested against production infrastructure, warmed, verified. The switch went out at 14:00, clean.

At 14:08, support tickets flood in. The bug: checkout fails for users who have a saved payment method and a non-US locale: a combination no smoke test exercised, because no smoke test knew about it