[ether_at_cpan]

They don't have to be real URLs, but just URIs. That is -- the files don't have to be accessable on the network at those URIs -- you can just use these strings as identifiers, and load the files up manually as you need them.

In fact, the JSON Schema specification even says that identifiers are just URIs and the evaluator implementation need not be expected to have to load the documents from the network (ref. https://json-schema.org/draft/2020-12/json-schema-core.html#... and https://json-schema.org/draft/2020-12/json-schema-core.html#...)