the LLM correctly diagnosed in minutes with links to relevant documentation

… said "whatever"; new Hibernate changed the persistence code so in this situation it calls `merge` instead of `save` (update rather than create AFAICT); there was no existing entity with the generated ID (of course, it's a new entity!); it fails. While my hypothesis was broadly right, that _particular_ issue would've taken me days to chase down -- but the LLM correctly diagnosed in minutes with links to relevant documentation. I vaguely hate LLMs, but this one saved me from a days long side quest that would've held up delivering the actual value of the project. …