I remember reading somewhere that spoilers, although I detest them as a matter of principle, don't actually detract from a viewer's response to a book. This is especially true if the spoilers allow the reader to pick up on clues that they might otherwise miss, like the fact the protagonist is
rubbing the scar on their finger, the finger that they mentioned in an earlier book as being sliced open. I don't know if that's a real spoiler by the way since I made it up but just on the off-chance it is, by sheer happen-stance, I blanked it.
Worst case scenario... you make your readers feel smart. I don't see how that's an issue.

I had a similar thing with Lacuna. One of my beta readers said that they saw
Sheng's betrayal coming a mile away and that it was far too obvious; yet none of my other readers picked up on the clues I left. Another reader said he correctly guessed the "wham ending",
Liao discovering that she's pregnant, very early in the book. Apparently the biggest giveaway I made was
I subtly implied, post fade to black, that the sex they were having wasn't protected. Both said they enjoyed the book regardless and I complimented them on their acuity.
In a way it's not bad. For example, in Harry Potter, aside from the last book you just *knew* Harry and the gang were going to survive, no matter how bad it got... I mean, really. You knew that right, deep down? Did it detract from the reading pleasure? No.
I think you'll be fine.
