Two or more controllers that jointly determine purposes and means must set out transparently, in a written agreement, their relationship and respective responsibilities for complying with the Law, in particular for data subjects' rights and the information duties. The essence of the agreement must be made available to data subjects; it may name a contact point, but data subjects may exercise their rights against each controller regardless.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.