Function cast_via_relay 

pub fn cast_via_relay<A: ToSocketAddrs>(
    addr: A,
    token: &str,
    device: &str,
    cmds: &[InjectionCommand],
) -> Result<RelayDelivery, AppError>

SENDER client: connect to a relay and post one or more commands for device, then read the relay’s delivery result for the first cast (bd-0b4e45) so the caller can tell whether the target device was actually connected. Casting to a plain omni daemon (which sends no result) yields acked == false.

Errors

Returns AppError::internal on connect / I/O failure.