This really is nothing new. EAI platforms have had to deal with this for years, they solve it with idempotent updates e.g. UPDATE WHERE rather than relying on

This really is nothing new. EAI platforms have had to deal with this for years, they solve it with idempotent updates e.g. UPDATE WHERE rather than relying on locks - ensure transaction tables have timestamps which can be used for this purpose. This also improves your throughput and avoids all the problems that locking brings e.g. deadly embrace and poor performance. Trying to perform guaranteed updates across HTTP transactions is always going to be tricky. The other factor is old database principals atomicity and ACID.