Adding entities with duplicate keys not handled gracefully

Adding two entities with different DNs but the same key is currently being reported as successful by the LDAP engine but is silently failing change detection, meaning that neither entity is actually committed to the connector, and no alert is displayed to the user.

If entities with duplicate keys accumulate in the change report, it might be possible to detect this and report failure on the LDAP response, avoid corruption of the connector space by committing only the entities already reported as successful, and displaying an alert to the user. This might also be an opportunity to implement user-cancellable warnings.

If the duplicate keys occur between a newly added entity and an existing entity and the DNs are different, this should be handled by rejecting the add request.