The server can prevent transitions from being carried out, e.g. due to the internal state of the vision system. A typical example would be to prevent leaving the parent state of a VisionStepModelStateMachine in order to avoid interrupting synchronization with an external system.
As automatic transitions are always done for internal reasons, the server will obviously simply not execute the transition in this case.
For method-triggered transitions, the server should set the Executable flag of the method in question to False to signal to clients that this method should currently not be called. If the method is called anyway, regardless of the Executable flag, the method shall fail with an appropriate error code.