Defines an explicitly supplied validator for one portable artifact profile.

A host supplies adapter modules per projection call. Descriptors are inert native JSON values; their canonical digest pins the producer contract. Adapters validate producer subject membership and completed variant coverage against caller-supplied original manifests and checked projections. They do not render, retrieve assets, start workers or register global capabilities.

Results and ownership

validate/2 returns a checked JSON projection or a located tagged error. DocShell checks the generic block and byte envelope before dispatch and contains callback exceptions, throws, exits and malformed replies. Producer semantics and format-specific validation stay with this adapter's owner. Core rejects variant media and subject kinds outside the descriptor before invoking validate/2; returned subjects must use the same declared vocabulary.