Protocol
A Protocol is how two Agents communicate along a single edge of a Topology — their established way of talking. It is not a primitive of the framework. It resolves into two things the framework already has: the channel the edge runs on (its medium, and how much of it there is — part of the Topology edge) and the Constraints on that channel (the rules of conduct — cadence, format, turn-taking, who may say what when). “Protocol” is the name for the two taken together on a given edge.
The everyday word “protocol” carries two unrelated things — a communication pipe (email, a chat tool, a pheromone, an ion channel) and a rule of conduct (a “meeting protocol”). In the framework the pipe is the channel and the rule is a Constraint, and a Protocol is the pairing of the two on an edge. The same pairing holds across scales: ion-channel signaling between cells, turn-taking in a conversation, message formats between software services. To a CEO it is the channel two teams use plus the rules of the road on it — the standup cadence, the format, who signs off before it moves.
The coupling a Protocol governs is the Causal-to-Computational Interface, where one Agent’s output becomes another’s input.