protocols

This is used to send back updated attributes on a group-seal, which lets
the application that SEALed see the full resolved group-membership
list.

This is needed for CDO selector based group declarations to
propagate the PMs idea about what is in the group to the
applications.

It's also useful to inform about the CDO IDs for batch-declared
name-string based CDO members of a group. In particular, transporting a
group-proxy CDO will always send CDO-IDs only, relieving the receiver
from doing name resolution.