A real incident where a silent Stripe API schema change caused 23 failed orders on a Friday night, with no HTTP error to signal the problem. The author built php-sentinel, an open-source PHP library that passively monitors API response shapes in production, learns a baseline schema, and alerts on drift (removed fields, type changes, nullable shifts, enum changes) before failures accumulate. Integrates with Guzzle, Laravel events, and Symfony. Available via Composer.