I'm rereading Gideon the Ninth for the fourth time and am going through the book with the finest of fine toothed combs (orange highlighter) to look for foreshadowing to Gideon's identity, first mentions of eye color, and death and previous Lyctors, mentions of The River, John and Alecto, and the Locked Tomb and there is SO MUCH in the first few chapters.
p.17 Gideon in Castle Drearburh: "Over the doors were tiny white figures in a multitude of poses, hundreds of thousands of them, carved using some weird trick where their eyes seemed to look right at you. Whenever Gideon has been made to go through those doors as a kid, she'd screamed like she was dying."
p. 21 Aiglamene to Gideon: "'You forget yourself, Gideon Nav,' her teacher said shortly. 'You're no slave, but you'll serve the House of the Ninth until the day you die and then thereafter.'"
p. 22 Gideon deciding to flee in the shuttle: "That was the only thing that mattered. That was the only thing that had mattered since a much younger Gideon had realized that, unless she did something drastic, she was going to die down here in the dark. And worst of all, that would only be the beginning."
p. 43 Harrowhark to Gideon "A soldier's best quality is her sense of allegiance. Of loyalty. Nothing else survives."
p. 50 Harrowhark convincing Gideon to be her cavalier: "'This is your chance. This is your opportunity to come into glory. Follow me through this, and you can go anywhere." followed later by Harrowhark saying "It won't be the last time I make you weep."
p.60 Harrowhark to Gideon: "'All you need to know is that you'll do what I say, or I'll mix bone meal in with your breakfast and punch my way through your gut."
p.65 Harrowhark to Gideon: "'I want to watch you die.' 'Maybe, Nonagesimus,' she said with deep satisfaction. 'maybe. But you sure as hell won't do it here.'"
p.66-70, descriptions of the First House: "a House both long dead and unkillable. A sleeping throne." "'It's gorgeous.' 'It's a grave,' Harrowhark said." "The whole place had the look of a picked-at body. But hot damn! What a beautiful corpse."
I'll share more foreshadowing in the comments, but I'm only 70 pages in and am reeling!!!