Configuring and adding custom package to kakoune in configuration.nix is not affecting kakoune

I am following the guide at the wiki.

My configuration.nix is at this link. I would like to configure kakoune to
a) use the cat assistant and
b) use the kakoune plugin at the BQN repository.

I have attempted following the steps and making a derivation similar in nature to kak-ansi. The plugin does not install, and the rc file doesn’t seem to have an effect. I would like to know how I can correct this to make my config work.