kakoune: prelude plugin fails to load on start

Describe the bug Here's a minimal nixos config installing kakoune with the prelude plugin:

home-manager.users.sebastian.programs.kakoune = {
  enable = true;
  plugins = with pkgs.kakounePlugins; [
    kak-prelude
  ];
  extraConfig = ''
    require-module prelude
  '';
};

After activating the config and running kak, I get an error in the debug buffer:

/home/sebastian/.config/kak/kakrc:6:1: 'require-module' no such module: 'prelude'
/nix/store/12awj62lp6sadx7v32zr4inx8b3xsw0a-kakoune-unwrapped-2020.09.01/share/kak/kakrc:29:1: 'evaluate-commands' 116:1: 'source' 6:1: 'require-module' no such module: 'prelude'
error while parsing kakrc:
    1:1: 'source' 29:1: 'evaluate-commands' 116:1: 'source' 6:1: 'require-module' no such module: 'prelude'

However, running the command require-module prelude in a kak client works without a hitch.

Expected behavior The prelude plugin is loaded on starting kakoune.

Notify maintainers

@vrthra @buffet

Metadata Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

 - system: `"x86_64-linux"`
 - host os: `Linux 5.4.96, NixOS, 20.09.20210218.6bebc91 (Nightingale)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.4pre20201201_5a6ddb3`
 - channels(root): `"home-manager-20.03, nixos-20.03.2685.977000f149b"`
 - channels(sebastian): `"home-manager"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute: pkgs.applications.editors.kakoune
# a list of nixos modules affected by the problem
module:

NixOS / nixpkgs

kakoune: prelude plugin fails to load on start #113733