> I seem to recall Meta/Facebook engineers on HN having said they have a tool that allows engineers to author SQL or ORM-like queries on the frontend and close to where the data is used, but a compiler or post-processor turns that into an endpoint.

I don't know about on-HackerNews but there's a discussion about their "all of Facebook optimizing compiler" infrastructure from when they did the site redesign in 2020: https://engineering.fb.com/2020/05/08/web/facebook-redesign/...

> perhaps not coincidentally, React introduced "server actions" as a mechanism that is very similar to [the above]

Yep - there's also the Scala framework LiftWeb (https://www.liftweb.net/), the Elixir framework Phoenix (https://www.phoenixframework.org/) and of course the system we're using right now (Arc) that do similar things. Scaling these kinds of UUID-addressed-closures is harder (because the client sessions have to be sticky unless you can serialize closures and send them across the network between servers).