flake: fixup multisystem switch

flake.nix

@@ -73,15 +73,20 @@
         (hostname: { system, ... }: system == x86_64-darwin)
         hosts;
 
-      mkDeploymentModule = targetHost: ({ lib, ... }: {
+      mkDeploymentModule = { targetHost, system, ... }: ({ lib, ... }: {
         options.deployment = with lib; {
+          system = mkOption {
+            type = types.str;
+            readOnly = true;
+            internal = true;
+          };
           targetHost = mkOption {
             type = types.nullOr types.str;
             readOnly = true;
             internal = true;
           };
         };
-        config.deployment = { inherit targetHost; };
+        config.deployment = { inherit targetHost system; };
       });
 
       baseHomeManagerModule = ({ ... }: {
@@ -114,8 +119,8 @@
         let
           pkgs = import nixpkgs { inherit system; };
 
-          machineRebuild = { system, ...}: 
+          machineRebuild = machine:
-            if system == x86_64-linux
+            if machine.config.deployment.system == x86_64-linux
             then pkgs.nixos-rebuild
             else inputs.nix-darwin.packages.${x86_64-darwin}.darwin-rebuild;
 
@@ -209,7 +214,7 @@
                   impermanence.nixosModules.impermanence
                 ])
                 ++ [
-                  (mkDeploymentModule targetHost)
+                  (mkDeploymentModule { inherit system targetHost; })
                   baseHomeManagerModule
                 ]
                 ++ extraModules
@@ -242,7 +247,7 @@
                 ])
                 ++ [
                   (baseDarwinModule system)
-                  (mkDeploymentModule targetHost)
+                  (mkDeploymentModule { inherit system targetHost; })
                   baseHomeManagerModule
                 ]
                 ++ extraModules