What is the right course of action?

Your answer is correct. According to German traffic rules, when you approach an intersection with a yield sign, you must give way to all vehicles on the priority road. In this scenario, the blue truck is coming from the left on the priority road and must be allowed to pass straight ahead first. The tractor, waiting to turn right, also has priority before you proceed. Your obligation is to wait and let both the truck pass straight and the tractor complete its turn before you go ahead. The blue truck does not have to yield to you because you are on the side road with the yield sign. This ensures safety and smooth traffic flow at intersections where priority is indicated by signs.