Major version supported; matched against the lesson's @<major> pin.
The ext type this handles, e.g. ext:acme-ordering.
OptionalresolveOptional parse-time transform, applied by parseLesson after the core
from_cards resolution - the extension analogue of a core resolver. Must
return a new lesson (no in-place mutation).
Validate one exercise of this ext type (its ext_payload). Returns an
empty array when the exercise is valid.
The engine-side implementation of one
ext:exercise type.typeis the full namespaced id (e.g.ext:acme-ordering);majoris the major version this implementation supports, matched against the@<major>a lesson pins inrequires_extensions.