So my attempt at a minimalist fix along the lines I suggested is at: https://github.com/chrisdennis/hibernate-orm/tree/HHH-10707

This is essentially just an update and slight polish of what I originally suggested. Nothing in the actual H2LC SPI is changed, just the way that the SPI is consumed by Hibernate. I believe it would also allow all implementations to continue behaving the way they currently do (with some possible tweaks to their reporting of the newly exposed failure conditions).