You said "you shouldn't smoke", which is a decision-theoretical claim, not a specification. It's consistent with EDT, but not CDT.

No it isn't, it's a statement about the universe: If you smoke, you'll get lesions. It's written into the specification of the universe; what decision theory you use doesn't change the characteristics of the universe.

In other words, you're denying the exact thing that CDT asserts.

No. You don't get to specify a universe without the kind of causality that the kind of CDT we use in our universe depends on, and then claim that this says something significant about decision theory. Causality in our hypothetical works differently.

Which is what a counterfactual is.

No it isn't.

Whatever your theory is, it is denying core claims that CDT makes, so you're denying CDT (and implicitly assuming EDT as the method for making decisions, your arguments literally map directly onto EDT arguments).

No it isn't. In terms of CDT, we can say that smoking causes the gene; this isn't wrong, because, according to the universe, anybody who smokes has the gene; if they didn't, they do now, because the correlation is guaranteed by the laws of the universe. No matter how much work you prepared to ensure you didn't have the gene in advance of smoking, the law of the universe says you have it now. No matter how many tests you ran, they were all wrong.

It may seem unintuitive and bizarre, because our own universe doesn't behave this way - but when you find yourself in an alien universe, stomping your foot and insisting that the laws of physics should behave the way you're used to them behaving is a fast way to die. Once you introduce a perfect predictor, the universe must bend to ensure the predictions work out.