A MQTTv5 broker implemented in safe Rust (using nom-rs, tokio, etc) will support cluster mode possible soundness issue with cluster mode client A connects and subscribes to topic T on cluster 1 client B sends message with QoS = 2 on topic T to cluster 2 client A disconnects cluster 2 forwards message to cluster 1 client A connects to cluster 2 and state is transferred cluster 1 processes message ??? client A never sees message