Function spawn_blocking_on_lsp_runtime 

pub fn spawn_blocking_on_lsp_runtime<F, R>(f: F) -> JoinHandle<R> 
where
    F: FnOnce() -> R + Send + 'static,
    R: Send + 'static,

IN.8b: the blocking sibling of spawn_on_lsp_runtime, for work that is genuinely synchronous rather than merely off-thread — spawning a formatter and waiting on its pipes.

spawn_blocking rather than spawn because a Command + wait_with_output would occupy a runtime worker for the whole run; on a current_thread runtime that is the actor thread, which is the no-UI-thread-work rule violated by a different route.