Function body_holding 

pub fn body_holding(
    body: BoxBody<Bytes, Box<dyn Error + Send + Sync>>,
    guards: Vec<Box<dyn Send + 'static>>,
) -> BoxBody<Bytes, Box<dyn Error + Send + Sync>>

Wraps body so guards are dropped only when the body reports it has finished (cleanly or with an error) or the returned body is itself dropped — never merely because the node that started the stream returned. This is what keeps balancer in-flight counters and limit-conn permits held for the stream’s real lifetime.