createCustomRecordTypeMap

One RecordType covering every declared custom type.

Custom records all share the custom typeName, and the store's type map is keyed by typeName — so the map gets one entry, not one per declaration. Validation and defaults dispatch on the record's own type, which is what keeps a review from being validated as a checklist.

A record whose type was never declared is refused rather than waved through: it would otherwise round-trip unvalidated and look like data the schema understood. With nothing declared the entry still exists and refuses everything, which is the same answer arrived at sooner.