Function map_outbound_error 

fn map_outbound_error(
    e: OutboundError,
    target: &Target,
) -> (&'static str, String)

Maps an OutboundError to the (code, message) pair used on this node’s error port. Shared by the buffered and streaming branches so a fix to one (e.g. a wording or timeout-classification change) can’t land in only one of them.