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

@@ -132,12 +132,14 @@
         pkgs = import nixpkgs { inherit system; };
       in
       {
-        devShells.default = pkgs.mkShell {
-          buildInputs = [
-            colmena.packages.${system}.colmena
-            agenix.packages.${system}.default
-            pkgs.openssl
-          ];
+        devShells = import ./devshells { inherit pkgs; } // {
+          default = pkgs.mkShell {
+            buildInputs = [
+              colmena.packages.${system}.colmena
+              agenix.packages.${system}.default
+              pkgs.openssl
+            ];
+          };
         };
         formatter = pkgs.nixfmt-tree;
       }