<objective Mock Stripe at the SDK layer and your tests pass green while production 500s the moment Stripe changes a response field — because the stub was never tied to a contract. This skill picks the right isolation strategy per dependency (in-process mock, HTTP stub, record-replay, fault injection, or ephemeral real service), stubs at the HTTP layer so tests survive SDK upgrades, and makes the CI run fail when any real call escapes the stubs. </objective Quick Route | Situation | Go to | |-----------|-------| | Node/browser test hitting an external HTTP API | MSW → | | Browser page driven b…