Something like:

{
  inputs = {
    flakelight.url = "github:nix-community/flakelight";
    devenv.url = "github:cachix/devenv";
  };
  outputs = { flakelight, devenv, ... }:
    flakelight ./. {
      devShell = { pkgs, inputs, ... }: devenv.lib.mkShell { 
        inherit inputs pkgs;
        modules = [
        ];
      };
    };
}

Something like:

{
  inputs = {
    flakelight.url = "github:nix-community/flakelight";
    devenv.url = "github:cachix/devenv";
  };
  outputs = { flakelight, devenv, ... }:
    flakelight ./. {
      devShell = { pkgs, inputs, ... }: devenv.lib.mkShell { 
        inherit inputs pkgs;
        modules = [
          # Your stuff here
        ];
      };
    };
}

for autoloading could have:

{ pkgs, inputs, ... }:
  inputs.devenv.lib.mkShell { 
    inherit inputs pkgs;
    modules = [
      # Your stuff here
    ];
  };

and put that in nix/devShell.nix or nix/devShells/devenv.nix or such

any idea why a package definition in nix/packages/example/default.nix, looking like this would complain lib.customisation.callPackageWith: Function called without required argument "buildPythonPackage" at /nix/store/... ?

{ buildPythonPackage }:

buildPythonPackage rec {
  pname = "example"....

haven't run into this with other packages I've defined wherein I use a bunch of build inputs from nixpkgs.
sorry for all the questions 😅