@jmgilman
Hocus builds a new VM for your project based on what you specify in hocus.yml. For Hocus in Hocus developement we use this VM image. All VM's are built using plain dockerfiles. I see no problem with creating a nix base image as long as some assumptions Hocus makes are fullfilled(a custom dtach binary, tmux is available etc...). Here is the base workspace image we currently use and you may infer from it what needs to be in the workspace image for Hocus to work.

Also you may specify a custom shell in your workspace tasks(if you want we may also add this feature for prebuild tasks) where you could launch nix shells for your developers :)

Also you may customize the internal VM images the agent uses for prebuilds and various tasks. Here are the Dockerfiles for those VM's.

So I see no problem in just using nix in the workspace image, I don't see whether Hocus needs to know about nix at all as we operate on VM's, as long as the assumptions we made about the VM images are fulfilled Hocus should work fine with Nix.

Perhaps I misunderstood this feature request? Could you please describe in detail what are you expecting from a Nix integration?

@jmgilman We're thinking of introducing per team/project buildkit builders. Instead of using docker we would use buildkit directly. Buildkit has support for mutiple frontends, especially for nix. Would the ability to directly specify the buildkit frontend in hocus.yml work for you?