I understand, my problem with understanding mirror was that this is part of the story. Sure, it doesn't specifically says that you need to help ghost or destroy mirror. Through the whole mission you are guided by ghost and instructed what to do. So instruction of destroying mirror felt a bit like objective even though it doesn't appear in objective screen.
Good example would be your Supreme Ghost report for The Dark Mod - Training mission, klatremus. You excuse all actions that bust ghost even though you don't have any objective that says to do training. Objective only says that there is no formal objectives and you can quit to menu. But even then you excuse that, because you are specifically guided by readables. In Scarlet Cascabel I'm guided by ghost. What do you think?