Packages are stored as pkg:deb/{name}, without a vendor and whichever configured archive they came from. Package rules may name a vendor the way PURLs usually do (pkg:deb/debian/curl, pkg:deb/ubuntu/curl); it's dropped, so a rule covers the package from every archive. The docs row warns that Debian and Ubuntu archives only keep the current version per suite.
The mirror can't fetch deb packages, so there's no mirror test.
Refs #306
