I was seeing a stack trace with this at the bottom:
error: cannot look up '<home-manager/nixos>' in pure evaluation mode (use '--impure' to override)
After reading a bit at https://nixos-and-flakes.thiscute.world/nixos-with-flakes/start-using-home-manager
I was able to craft this shape which uses home-manager in a flake and
doesn't have the same problem.
