There is no point spamming a list for every function call, there is no
use case where multiple notify callbacks would be useful.

First step to making it a fatal error.

If no ADD_ROUTE message has been received from the master associating a
stream with a particular context ID, then it is expected messages
originating from that context ID can only be routed via the parent.

inspect module includes the staticmethod decorator added by
a8d1dc67304d678e9e94ebb64be259e958181b63