reproduction for bug report

flake.lock

{
  "nodes": {
    "flake-utils": {
      "inputs": {
        "systems": "systems"
      },
      "locked": {
        "lastModified": 1731533236,
        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
        "owner": "numtide",
        "repo": "flake-utils",
        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
        "type": "github"
      },
      "original": {
        "owner": "numtide",
        "repo": "flake-utils",
        "type": "github"
      }
    },
    "microvm": {
      "inputs": {
        "flake-utils": "flake-utils",
        "nixpkgs": "nixpkgs",
        "spectrum": "spectrum"
      },
      "locked": {
        "lastModified": 1741893540,
        "narHash": "sha256-NEsR+FQ+AsY4cOZ3OL69JVdPTAYzSzBqeAhHGRRuDGk=",
        "owner": "astro",
        "repo": "microvm.nix",
        "rev": "5bbc126db87b5ffc36394df630eead403c48fac8",
        "type": "github"
      },
      "original": {
        "owner": "astro",
        "repo": "microvm.nix",
        "type": "github"
      }
    },
    "nixpkgs": {
      "locked": {
        "lastModified": 1733212471,
        "narHash": "sha256-M1+uCoV5igihRfcUKrr1riygbe73/dzNnzPsmaLCmpo=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "55d15ad12a74eb7d4646254e13638ad0c4128776",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixos-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "nixpkgs_2": {
      "locked": {
        "lastModified": 1742422364,
        "narHash": "sha256-mNqIplmEohk5jRkqYqG19GA8MbQ/D4gQSK0Mu4LvfRQ=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "a84ebe20c6bc2ecbcfb000a50776219f48d134cc",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixos-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "microvm": "microvm",
        "nixpkgs": "nixpkgs_2"
      }
    },
    "spectrum": {
      "flake": false,
      "locked": {
        "lastModified": 1733308308,
        "narHash": "sha256-+RcbMAjSxV1wW5UpS9abIG1lFZC8bITPiFIKNnE7RLs=",
        "ref": "refs/heads/main",
        "rev": "80c9e9830d460c944c8f730065f18bb733bc7ee2",
        "revCount": 792,
        "type": "git",
        "url": "https://spectrum-os.org/git/spectrum"
      },
      "original": {
        "type": "git",
        "url": "https://spectrum-os.org/git/spectrum"
      }
    },
    "systems": {
      "locked": {
        "lastModified": 1681028828,
        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
        "owner": "nix-systems",
        "repo": "default",
        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
        "type": "github"
      },
      "original": {
        "owner": "nix-systems",
        "repo": "default",
        "type": "github"
      }
    }
  },
  "root": "root",
  "version": 7
}

flake.nix

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
    microvm.url = "github:astro/microvm.nix";
  };

  outputs = {
    self,
    microvm,
    nixpkgs,
  }: {
    nixosConfigurations.demo = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
        microvm.nixosModules.host
        {
          microvm.vms.demo_guest.config.imports = [
            microvm.nixosModules.microvm
          ];

          # dummy values
          boot.loader.grub.devices = ["/dev/sda"];
          fileSystems."/" = {
            device = "/dev/sda1";
          };
        }
      ];
    };
  };
}