Also, if you really want to write code that's agnostic to whether you're working directly on the DB object or a transaction, you can just declare that interface yourself; it's not like in java where the implementing class has to opt in.

The absence of the interface being predeclared for you does mean more boilerplate, but I agree that transactional vs. not doesn't strike me as a good thing to be hiding; this particular case seems like maybe a very reasonable omission. I try to avoid abstractions that leak.