The CDZ message is answer at the ingame message about coal, I made last turn. I have and was saying we need an ally other than Ama.
About the Ama ships at our shores, naturally can they land and make a merchant-action in turn, without our seeing; but why did they need 2 ships for it (a gallon and a cara), that is my question. I haven't looked at the F4-tech the last turns, so I don't know, if they get money. In the moment (T 1360) they couldn't make spy action at us.
About buildings against espionage, if you use them, you need them in every town, so its expensive. the more important is making active esp, with commerce and counteresp actions. The bigger disadvantage is changing civics 5 turn wait to rechange and anarchy additional, The bad thing about it is that you don't have to wait 5 turns as enemy.
btw
Alpha building RR in some direction is automatically imo. Its making impossible to plan amnd then see the units are not there anymore.