Function forward_broadcast_to_channel 

pub(crate) async fn forward_broadcast_to_channel(
    client: &Client,
    local_url: &str,
    auth_key: &str,
    req: &BroadcastForward<'_>,
) -> Result<(), String>

Asks the instance at local_url (another channel on this machine, its auth_key from the shared registry, same user) to deliver one broadcast. A channel from before the route answers 404 and is named as such, for that target only.