This leads back to my original statement of "What's the value of doing this?". Yes, if you put this in the presavehook of the business object, you would now have "holes", if and only if, a save 'failed' and the new id number would not be 'rolled back'. You would also, theoretically, have this event stored in the errorlog table if this did happen, so the 'holes' would have some sort of audit trail to provide an explanation. Is this good enough? Only you know this answer.

As I mentioned, I did not invest the time and effort into changing this part of the framework, so I cannot advise how to get this into the TRANSACTION boundary. If you want to go forward with this, I'm sure someone else would be able to give you good advice here on the UT.

Good luck!