Taking card payments is an optional module, but the Store's node types named one directly. A deployment that did not mount it could not compile them at all — CS0234: the type or namespace name 'Payments' does not exist in the namespace 'MeshWeaver' — and pages with nothing to do with money rendered blank.

The platform now ships IPaymentProvider in MeshWeaver.Mesh.Contract: a provider-neutral contract for opening a hosted checkout, cancelling a subscription at the end of its paid period, verifying and reading a webhook delivery, and asking whether the processor can actually reach this portal. A payment module supplies an implementation; a portal that mounts none simply resolves nothing.

The absence is a state, not a null to guard. hub.PaymentProvider() returns null on a portal that does not sell, and every commerce surface answers that case explicitly — a refusal with a sentence in the viewer's language, a payment-path report that says out of scope rather than healthy or broken. No reflection probe for an assembly, no try/catch around a payment type.

The reasoning, and the shape a second provider implements, is in The Payment Provider Contract.