> your side effects (e.g. database writes) aren't idempotent

What does idempotent mean in this context, or did you mean atomic/rollback on error?

I'm confused because how could a database write be idempotent in Django? Maybe if it introduced a version on each entity and used that for crdt on writes? But that'd be a significant performance impact, as it couldn't just be a single write anymore, instead they'd have to do it via multiple round trips