start
Parses an OpenID4VP request delivered through the Digital Credentials API (OpenID4VP 1.0 Appendix A), as Credential Manager hands it over: protocol (openid4vp-v1-unsigned, -signed or -multisigned), its requestData (the request's data object, as JSON) and the calling page's or app's origin. It's answered as a presentation from startPresentation, but Presentation.respond and Presentation.decline send nothing: each returns, in Presentation.Presented.dcapiResponse, the response's data for the platform to hand back.
origin must be one the platform verified: Credential Manager's CallingAppInfo.getOrigin for a privileged browser, or the calling app's signing-certificate origin. Never take it from the request: an unsigned request names no Verifier but its origin, and presented copies are bound to it. A request that can't be parsed is WalletException.Code.invalidInput.