* checks using package providing the nix-daemon that we'll be using
* made optional (unlike some other config checks) "just in case":
since this requires running the new Nix on the builder, this
won't work in a few (AFAIK very uncommon) situations such as
cross-compiling NixOS or using `include` directives in nix.conf
This does rely on Nix2 but not by the builder.
Since we only offer Nix2+ in-tree this should be fine,
and may otherwise be required anyway.
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