Source code and abstract virtual machines make many things easier. However, I expect Rails is typically deployed via Docker or something to capture dependencies

Source code and abstract virtual machines make many things easier. However, I expect Rails is typically deployed via Docker or something to capture dependencies. That part could be replaced by Nix, in principle. People also use Nix quite in combination with Docker, so clearly Docker doesn't go far enough on the developer experience, and Nix doesn't provide isolation so Docker provides advantages from that side. I feel like there should be a more integrated, comprehensive solution for this sort of thing, but these are on the right track.