One possible solution for MappingContributors: we could just hide the SearchMappingRepositoryBuilder from users (move it to SPI), and expect each mapper to provide its own API to bootstrap it: it would just create its own SearchMappingRepositoryBuilder.

Then each mapper could optionally offer an SPI accepting a SearchMappingRepository allowing to bootstrap multiple mappers together in the same SearchMappingRepository, but that would be advanced use. And let's be real, very few users will need this.