Function trace_backend_request 

pub async fn trace_backend_request<Fut, T>(_cmd_id: u16, future: Fut) -> T
where
    Fut: Future<Output = T>,

Record a backend request span for the API request currently executing on this Tokio task. Calls outside public API dispatch are intentionally no-op, matching C++’s explicit ReqReply_RelatedAPISvrReq linking model.