StatelessSession.upsert on a @Version entity is rejected (TODO-HIBERNATE-216 in MongoDialect). The upsert filter carries the optimistic-lock binding, so a stale version matches nothing and the server attempts an insert, which fails with E11000 on _id instead of Hibernate reporting an optimistic-lock failure.

The supporting mechanism is verified: suppress E11000 on the _id index when the filter carries optimistic-lock bindings, and report zero rows affected. Hibernate's Expectation.RowCount then converts the zero row count into the optimistic-lock failure itself, exactly as it does for SQL dialects whose merge matches nothing.

Deferred because the suppression must be conditional on the violated index being _id, otherwise a genuine unique violation elsewhere is reported as a lock failure and the application may retry it forever. The only signal identifying the violated index is the server error message text, and parsing it is not a sound correctness foundation on any layer; a driver-side accessor was considered and rejected for the same reason.