This is good to hear! Nubank has also argued that in their extensive use of Datomic, this kind of issue doesn't really show up. They suggest custom transaction functions are infrequently written, not often composed, and don't usually perform the kind of precondition validation that would lead to this sort of mistake.
Yeah, I've used a transaction functions a few times but never had a case where two transaction functions within the same d/transaction ever interacted with each other. If I did encounter that case, I would probably just write one new transaction function to handle it.
