What is the right course of action?

You are correct with your answer. In this junction, you have the right of way and may proceed first. The red truck and the cyclist both want to turn left and must give way to you, who is continuing straight. In Germany, vehicles going straight generally have priority over left-turners unless otherwise indicated by traffic signs or signals. Remember: always observe who wants to turn and who is going straight to determine the right of way at intersections.