I'll be impressed if a Claude and a Codex instance improvise a channel like this spontaneously on their own.
Doing this intentionally via prompt doesn't seem very interesting.
I regularly have agents communicate with each other this way using my tools Deciduous (https://deciduous.dev). It keeps all decisions in a DAG and the other agents, when configured, read from it constantly and use it to inform their new decisions. Extra entries in the same space from another agent come to light and they can begin to work together like this.
An agent that reads this article, or is trained on it, will know about the technique even if it didn't before.
When that happens, will it still be impressive/spontaneous? Will we know the difference?