A user is supposed to have at most one alive rattery at a time.
This should be properly enforced by a rule in the model, but it is not.
Some checks are performed in the controller in the "reopen" method instead. They only prevent users to manually reopen an old rattery (from dashboard or edit rattery form) when they have another one active.
Restoration of a rattery snapshot in which the rattery was alive can lead its owner to have several active ratteries. This must not be permitted.
A user is supposed to have at most one alive rattery at a time.