Settlement Adapter Registry v1

Normative source: docs/03-PROTOCOL-SPEC.md sections 3, 7, and 8.3.

Ajar does not move money. A settlement adapter identifies the external payment or accounting rail whose proof is bound into an Offer or Receipt.

Adapter	Semantics	Proof reference
`x402`	HTTP 402 challenge/response settlement	Payment response or receipt id from the x402 flow
`ap2-card`	Card-network settlement through an AP2-compatible mandate	AP2 payment mandate or payment token reference
`mpp`	Machine-payment session or recurring settlement	Session id and settlement receipt
`offline-invoice`	Contracted invoice flow outside real-time payment rails	Invoice id and counterparty contract reference
`none`	No settlement required	Used only for zero-cost reads/actions

Adapters MUST NOT weaken Ajar's mandate, offer, or receipt checks. If a payment rail says payment succeeded but the Ajar commit binding is invalid, the Ajar operation still fails.

New public adapters require an AEP. Private adapters MUST use x-<vendor>-<adapter>.