use a filter_activator_class to only let "engineer" pass
*sigh* I gotta say this entity has caused more confusion since TF2 came out than I've ever seen. It does
not refer to TF class (it would probably be filter_activator_tfclass, like the tfteam one), but rather refers to entity class. That is, it filters to a type of entity... func_physbox, prop_dynamic, npc_antlion, etc. All players are of the "player" entity, so it doesn't help. There is currently no way to filter for TF class type.