Validating against RM schemas in the REST API

How are we handling differences in API request / response payloads to the schemas for canonical JSON and XML?

Some payloads won’t validate against the schemas, for instance, missing contribution.uid on POST /contribution, or contribution.versions being a list of VERSION (API schema) instead of OBJECT_REF (RM schema).

Note in the case of the missing fields, like uids, that can be handled by a relaxed schema setting that as optional, but in the case of the OBJECT_REF to VERSION resolution, that is a totally different schema for the API not a relaxed one.