ci: strengthen NixOS checks

hosts/default.nix

@@ -47,9 +47,8 @@ let
           ;
       };
     };
-in
-{
-  flake.nixosConfigurations = {
+
+  nixosConfigurations = {
     nix-example = mkSystem {
       host = "nix-example";
       system = "x86_64-linux";
@@ -102,4 +101,13 @@ in
       };
     };
   };
+in
+{
+  flake = {
+    inherit nixosConfigurations;
+
+    checks.x86_64-linux = lib.mapAttrs' (
+      name: nixos: lib.nameValuePair "nixos-${name}" nixos.config.system.build.toplevel
+    ) nixosConfigurations;
+  };
 }

hosts/installer/default.nix

@@ -9,6 +9,8 @@
     "${modulesPath}/installer/cd-dvd/installation-cd-minimal.nix"
   ];
 
+  boot.zfs.forceImportRoot = false;
+
   networking = {
     hostName = "nixos-installer";