So... separating front-end from back-end in and of itself is not necessarily a problem, but using async to do it adds complexity that is not worth it. Originally, I was hoping that a CRDT or similar mechanisms could be used to smooth out all such problems in a general way (including letting plugins contribute their annotations without causing jank on the main thread), but I discovered that such a collaboration layer cannot hide the underlying explosion in the potential state space.

I wrote about this in some detail: https://raphlinus.github.io/xi/2020/06/27/xi-retrospective.h...

Maybe it would have been better to embed the core inside platform-specific front-end apps using a synchronous FFI. But then, you also discovered that the platform-native GUIs are overrated, at least for this application.

Addendum: One thing that excites me about Rust is the potential to cut down on the excessive use of IPC, by letting us implement reusable libraries in a safe language that imposes minimal runtime requirements, then use Rust's powerful metaprogramming features to auto-generate safe language bindings for those libraries. That's one reason I chose Rust for AccessKit. I know diplomat [1] is making some progress in this area.

[1]: https://github.com/rust-diplomat/diplomat