fix: work on making the installer work offline

fix: ensure system closure is installed for derivations needed by the installer

fix: build closure in build-step instead of on iso

installer/artifacts.nix

@@ -20,6 +20,12 @@ let
       targetConfig = self.nixosConfigurations.${hostName}.config;
       targetSystem = targetConfig.system.build.toplevel;
       diskoScript = targetConfig.system.build.diskoScript;
+      
+      # Build the closure export at build time (not runtime in ISO)
+      closureExport = pkgs.runCommand "closure-export-${hostName}" { } ''
+        mkdir -p $out
+        ${pkgs.nix}/bin/nix-store --export $(${pkgs.nix}/bin/nix-store -qR ${targetSystem}) > $out/closure.nar
+      '';
     in
     nixpkgs.lib.nixosSystem {
       inherit system;
@@ -29,6 +35,7 @@ let
           hostName
           targetSystem
           diskoScript
+          closureExport
           ;
         hostPlatform = system;
       };