How lovely! I enjoyed the way you wove the different concerns of the characters - Harry's flashbacks, Snape's troubles with the castle - into a heartwarming tapestry.
This line made me laugh out loud: "Truth #1: He was Harry Potter. He always started with this one. It made him feel good to get it right. If he ever got it wrong, he figured he was so screwed that none of the rest mattered." I've had mornings like that.