`meta.nixpkgs`

[blaggacao]

I think this interface is not necessary and using the equivalent upstream interfaces would imo lead to less confusion.

• In a flakes world, imo, the way to determine meta.nixpkgs would be as follows: inputs.colmena.inputs.nixpkgs.follows = "";

[blaggacao]

Since eval.nix is currying the target, but otherwise isolated, we don't have access to the colmena flake.

The obvious alternative is to require a contract on inputs.nixpkgs on the target flake.