Function idle_timeout_body 

pub fn idle_timeout_body(
    body: BoxBody<Bytes, Box<dyn Error + Send + Sync>>,
    idle: Duration,
) -> BoxBody<Bytes, Box<dyn Error + Send + Sync>>

Wraps body so it errors when no frame arrives for idle. The timer resets on every frame, so a steady stream survives indefinitely while a silent one is reaped — and reaped as a real failure (Poll::Ready(Some(Err(IdleTimeoutError)))), not a clean end: ending cleanly would write the chunked terminator (HTTP/1.1) or END_STREAM (h2) exactly as a legitimately complete response would, making a truncated body indistinguishable from a complete one on the wire — on exactly the unbounded bodies (NDJSON exports, log tails, bulk proxied data) this feature targets. A real upstream error — the wrapped body itself yielding Err, e.g. a connection reset — is forwarded unchanged; the reap only fires when nothing else has.