Describe the bug

Since #12979 not only the behavior of locking is changed, but also the behavior of nix build and nix eval.

Steps To Reproduce

$ nix --version
nix (Nix) 2.28.1
$ nix registry add p nixpkgs
$ nix eval p#path
/nix/store/0d3h8gi2q46fb4l563h6pginjw2a90r4-source

$ nix --version
nix (Nix) 2.29.0pre20250418_f683a55
$ nix registry add p nixpkgs
$ nix eval p#path
error: cannot find flake 'flake:p' in the flake registries

Expected behavior

nix build and nix eval should also respect the user registry.

Metadata

Additional context

Checklist

• checked latest Nix manual (source)
• checked open bug issues and pull requests for possible duplicates

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