Returns the full reference catalog — conditions, medications, nicotine options, spelling corrections, plus the legacy corrections + products lists — in one typed, envelope-wrapped response. Every row is self-contained: condition rows carry their treated_with[] medications inline, medication rows carry their used_for[] conditions inline, spelling-correction rows carry their {from, to} mapping. There are NO response-root relationship maps; consumers walk one row to render any relation, in any direction, pre-sorted by prescription_count descending. Returns every dataset by default; pass include to narrow to specific categories, or fields=meta for a cheap names-and-versions check that skips the multi-megabyte row payloads. Honors ETag / If-None-Match so an unchanged catalog returns 304.