The Datastar API itself is very simple, 3 functions or so, I ended up wasting a lot more time on stuff like leeping the SSE stream open, compression support (zstd only atm), and trying to use CLOS in a way that would fit both Hunchentoot and Clack (not always easy).

Have you tried wookie? Such extreme case of blocking the event loop... negates any benefit of async processing.