Package files outside Hashed/, such as All/{name}-{version}.pkg from
repositories built without pkg repo --hash and the bootstrap
Latest/pkg.pkg, were relayed without any checks. They are still passed
through uncached, since their names can be reused for rebuilds, but a
versioned name is now checked against the denylist first, and while a
scanner covers freebsd they are refused, because only cached artifacts
can be scanned.
Catalogues (meta.conf, packagesite and data) carry their signature
inside the archive and go through the metadata cache byte for byte.
Packages under Hashed/ have the content hash in their name, so they go
to the artifact cache as pkg:bsd/freebsd/{name}@{version}. Other files,
including the bootstrap files under Latest/, are passed through.
pkg.freebsd.org is the built-in freebsd repository; more mirrors go
under upstream.freebsd.
Closes#536
