Most of our events do in fact represent the state change as the mutation. However I see no complexity issue with how we implement CAS semantics. Its 100% equiv

Most of our events do in fact represent the state change as the mutation. However I see no complexity issue with how we implement CAS semantics. Its 100% equivalent to any other implementation with all the implications -- reduced concurrency being the primary issue. We avoid this at all costs for most objects and, like you suggest, resolve conflicts by de-duping events or combining state changes to the final aggregate.