If you use a content-addressable scheme (fetchurl with sha256, for example), it will retain the source archives until you run garbage collect. If you use built

If you use a content-addressable scheme (fetchurl with sha256, for example), it will retain the source archives until you run garbage collect. If you use builtins.fetchTarball, I don't think this is the case. Since this all uses CAS, you can use the nix prefetch scripts to import an arbitrary file:// or other URI into the nix store.