A podcast with a handful of nerds talking about nerdy stuff... (but mostly roleplaying games)
I would think Defend the Tower of Luck would happen first - you get a cube, and at the same time you are placing the cubes on the buildings that accumulate them and the VPs on the Builders Hall building, etc. All that stuff before the actual turns start. Then the Ambassador is just the first "agent" placed once the turns actually start. That's how I think about it all anyway.
This makes the most sense to me as well.