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).
And perhaps not coincidentally, React introduced "server actions" as a mechanism that is very similar to that. Engineers can author what looks, ostensibly, like frontend code, merely splitting the "client" side and "server" side into separate annotated functions, and the React bundler splits those into client code, a server API handler, and transforms the client function call into the annotated server function into an HTTP API call.
Having used it for a bit it's really nice, and it doesn't result in yielding so much control to a very complex technology stack (GraphQL batchers, resolvers, etc. etc.)