I was thinking about this question in regards to whether CDT agents might have a simply bayesian reason to mimic UDT agents, not only in any pre-decision signaling, but also in the actual decision. And I realized an important feature of these problems is that the game ends precisely when the agent submits a decision, which highlights the feature of UDT that distinguishes its cooperation from simple bayesian reasoning: A distinction that becomes important when you start adding qualifiers that include unknowns about other agents' source codes. The game may have as many confounders and additional decision steps before the final step, but UDT is exclusively the feature that allows cooperation on that final step.