pass inputs in container friendly way

common/flakes.nix

@@ -1,4 +1,4 @@
-{ lib, pkgs, config, inputs, ... }:
+{ lib, pkgs, config, ... }:
 with lib;
 let
   cfg = config.nix.flakes;
@@ -15,7 +15,7 @@ in {
       '';
 
       # pin nixpkgs for system commands such as "nix shell"
-      registry.nixpkgs.flake = inputs.nixpkgs;
+      registry.nixpkgs.flake = config.inputs.nixpkgs;
     };
   };
 }