Could Draco's assignment be considered two seperate tasks?

1. Fix the Cabinets so the Death Eaters can get into Hogwarts.

2. Kill Dumbledore.

If so, could Snape have been vowing to make sure Draco got the cabinets fixed? Who's to say the twitch in his hand during that part of the vow wasn't him thinking "yeah, I'll make sure he gets the cabinets fixed, but you can forget the second task!" Narcissa only referred to one task right?

Just a thought! I really don't think it'd be that simple though!