In reply to @isofruit "Modelling one was the": hmm, so source is a singleton
and case-2 is problematic. Since a new consumer appears or gets attached
"somewhere" at the end of a chain and the source cannot know (a) a new-consumer
arrived and  (b) needs data that has already been pushed down some chains. In
that case some sort of 'event' needs to bubble-up from the new consumer
up-the-chain, reaching the source. Saying "i'm the new consumer, you can reach
me thru the path, which is included in the 'event-data', know pls send me a
state..