Dispatches on the source's cache$builder: obo fetches the ontology
release, hgnc_tsv fetches the HGNC complete set. Identifiers that match the
source pattern are written to the cache directory as a snapshot, and a
retired-id map, when the builder produces one, to the matching
<version>.retired.tsv sidecar. An OBO version defaults to the ontology's own
data-version; an HGNC version defaults to the source's default_version.