The data layer is responsible for serving the payloads of objects.
We _could_ have Bob go to alice and systematically call each message in a row, but that's a waste of time and energy.
Better would be to provide a single endpoint on the server where I can say "give me all objects from Alice that were sent to Bob or are marked as:Public starting with id <foo>"
This may be attached to Alice directly but it doesn't have to be: it could be a generic per-server endpoint.
6/