After mulling over this for six months and doing two overly complex prototypes, I've come up with something that works well enough and fits under 500 lines of code. Six months to think, one day to write. I had to let go of using a spaced repetition algorithm because that requires statefulness, and I wanted a stateless minimal solution.
If you have a fediverse account, you can quote this note from your own instance. Search https://fantastic.earth/users/abnv/statuses/115568841298323057 on your instance and quote it. (Note that quoting is not supported in Mastodon.)
RE: https://fantastic.earth/@abnv/115568841298323057
My feed repeater has been bringing up great gems from the past, such as: https://nbviewer.org/url/norvig.com/ipython/xkcd1313.ipynb by Peter Norvig.