Hello in MQTT is possible to make one retain message on each topic. This message device get first when connected to MQTT and subscribe on topic. It is somethink like that for particle cloud broker? (In MQTT it is limit one retain message on each topic, will be greate to have one retain message on each topic and each coreid device)
(It is will be good to using when device sleep all time then wake up, get retain message and check if it have some command from cloud, then do they work and go sleep again)