Note though that another option is to use MathJax or KaTeX at build time (e.g. as preprocessing or postprocessing to the Hugo build here), to generate a static page that does not require Javascript to render.
MathJax: https://docs.mathjax.org/en/latest/server/start.html
KaTeX: https://katex.org/docs/api#server-side-rendering-or-renderin...
I just want to clarify one thing that I didn't think to mention (but probably should have) in the article itself. I went out of my way to use eqn specifically because I wanted to use that particular tool here. I write LaTex a lot on a day to day basis, and wanted to play around with something else. So this wasn't a case of picking eqn because I thought it was the best tool for the job.
Using the eqn and troff suite in 2025 ... I'll just say there's a better way. LaTeX is arcane enough, but at least it is a universal standard in mathematical publication that it pays off to learn a little.