Function annotate_current_span 

pub fn annotate_current_span<A, E, R>(
    key: &'static str,
    value: impl Into<String>,
) -> Effect<A, E, R>
where
    A: AnnotateCurrentSpanSuccess + 'static,
    E: AnnotateCurrentSpanErr + 'static,
    R: 'static,

Adds key → value to the current span’s annotation map (fiber-local).

Generic over A, E, and R for composition with other Effect<A, E, R> graphs. In practice A is unit and E is Never (see AnnotateCurrentSpanSuccess, AnnotateCurrentSpanErr). The body does not read R; nested fiber ops still use run_blocking with () where those effects require it.

Type inference often needs an explicit turbofish, e.g. annotate_current_span::<(), Never, ()>(key, value) or ::<(), Never, R> under a generic env.