I found a GitHub repository today that, although not the main point of it, serves as an excellent example of how to use Nix for NPM and Python projects. Here's the link: https://github.com/schlarpc/re-shell/. I found it via this post from HN today, and it's nominally a reverse engineering environment. However, in documenting how to add packages for uv (Python package manager), npm, and through the Nix flake, it has actually very nicely made it easy for a human who doesn't quite grok Nix development shells to do so. Props to Chaz Schlarp!