I don't think we should always blindly use limit=1 with one() because sometimes it's also an implicit assert that there should only be one row returned in that result set.  In this case, there should only be 1 open sms session per connection, and we enforce that on session start by closing any open sessions for that connection.  If we use limit=1 here and there happen to be two sessions open because of a system glitch, it will just pick one and count the answer against it (which would be bad). So if there's two sessions open, we want this to raise an exception (MultipleResultsFound).