add devshells

common/nix.nix

@@ -13,6 +13,9 @@
     trusted-users = [ "root" ];
     auto-optimise-store = true;
   };
-  nix.registry.nixpkgs.flake = inputs.nixpkgs;
+  nix.registry = {
+    hd.flake = inputs.self;
+    nixpkgs.flake = inputs.nixpkgs;
+  };
   nixpkgs.config.allowUnfree = false;
 }

devshells/default.nix

@@ -0,0 +1,6 @@
+{ pkgs }:
+{
+  agda = pkgs.mkShell {
+    buildINputs = with pkgs; [ agda ];
+  };
+}

flake.nix

@@ -132,13 +132,15 @@
         pkgs = import nixpkgs { inherit system; };
       in
       {
-        devShells.default = pkgs.mkShell {
+        devShells = import ./devshells { inherit pkgs; } // {
+          default = pkgs.mkShell {
             buildInputs = [
               colmena.packages.${system}.colmena
               agenix.packages.${system}.default
               pkgs.openssl
             ];
           };
+        };
         formatter = pkgs.nixfmt-tree;
       }
     );