Gateways are adapters behind one interface, with capabilities DECLARED rather
than assumed -- because gateways are not interchangeable. Some have no
authorize-then-capture, some cannot refund partially, some have no vault. An
interface that pretends otherwise fails at the moment money should have moved.
So capabilities are declared, refused loudly when absent, and checked at build
time where the gateway is statically known.
Tier 1 is sandbox, Stripe, Razorpay and PayPal. Stripe and Razorpay are
deliberately the first real pair because they DIFFER on capture model, currency
spread and refund semantics -- one gateway does not prove an abstraction, and
two similar ones prove it badly. Tier 2 and a regional Tier 3 follow, and
defineGateway() makes a third-party adapter a first-class citizen held to the
same shared contract suite.
Two rules shape the package: it never touches a raw card number (hosted fields
keep an application in PCI SAQ-A rather than SAQ-D), and the signed webhook is
the source of truth rather than the browser redirect, which is a claim from an
untrusted client.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
