Finally switched my blog to self-host the fonts. Seems like some improvement on the "flash of unstyled content" but it's still there somewhat with
font-display: swap. I'm giving it a try with that left unset, which means the text area is briefly blank on first load, but that feels less jarring than actually swapping the fonts.
Instead of starting on the Ergo dataflow UI, I instead did some extra testing, adding a full integration test against the real server, and checking that it properly works with the triggers and actions systems.