I wrote:
Let's see -- here are the options I can see (after an IRC chat): (...) 2) Catch this case and instead return a generic "something is wrong" - MDB_BAD_TXN or MDB_INCOMPATIBLE. (...)
Duh, I forgot
(6) Like (2) but create a new error code after all. Then we can document in its description that it's not caught reliably. That wasn't hard:-)