Function catch_unwind_future 

pub fn catch_unwind_future<F: Future>(
    fut: F,
) -> impl Future<Output = Result<F::Output, Box<dyn Any + Send>>>

catch_unwind for futures (std has no FutureExt::catch_unwind): each poll of fut runs under catch_unwind, so a panic raised at any await point inside fut surfaces as Err instead of unwinding the loop task.