Function try_cloud_relay 

async fn try_cloud_relay(
    state: &AppState,
    req: &InjectionRequest,
) -> Option<Value>

Tier 4. Some(body) when the cloud accepted the injection (and the sender echo has been emitted); None when tier 4 doesn’t apply or didn’t take, leaving the caller to return its original error.

Queued is not delivered. The cloud persists the message and wakes subscribed sidecars; the recipient’s srv picks it up on its next sync, which may be seconds away or never if that instance is offline. success: true here therefore means “handed to the relay” — which is the strongest claim any WAN tier can make, and is what DELIVERY=wan on the echoed marker already tells the sender.