Ah. I can see why you worried about my request, but this is much better than anything I could have described wanting, myself. What a cunning, delightful present!
The intelligence implicit in the way that one sentence after the other is crafted here just knocked me back. Sometimes it's done with a light, deft hand, folding in a touch of humor that made me smile:
The blade was ready, a stupendous monument to Godric Gryffindor's inadequacy issues, and the hilt was a work of art, a bejewelled glorification of bloodshed.
And at other points the phrasing packs even more punch, because so much information is conveyed with such economy, bordering on wordplay:
He thought it was Hagrid who might have told him once that Dumbledore trusted Severus to the hilt, and Horace knew well where his own heart lay.
It's easy to get distracted by the excellence of the writing, and I don't want to overlook the marvelous job you do here with Snape's characterization. Ah, now this Snape is one I would love to read much, much more of. He lives and breathes here and I relished seeing how his mind works. Such a meaty, satisfying Snape you've got here. And Slughorn! I never would have guessed that you could make me feel pity for the man. But I do: this Slughorn is repellent, sad, and terribly appealing, all at once.
And with all that---elegant prose, deft humor, and memorable characterizations---you even gave me a plot as well. And a smart one! My cup runs over, truly. And the resolution of the plot problem you've set for Snape ties in with the resolution of their relationship, and it all works so very well.