How is genocide repudiated in this novel?
Well, admittedly, the book doesn't end with a long epilogue chapter titled "Genocide is Really, Really, Bad, Mmmkay?" However...
The end of the novel is hardly celebratory. Ender is forced into exile, his sadistic Battle School washout brother becomes Hegemon of Earth (while also losing the only moderating influence, their sister Valentine who leaves Earth to travel with Ender), Ender does start a new secular religion, whose success destroys his war-hero status.
The best thing that happens is Ender discovers the Buggers aren't all dead. He finds a Hive Queen egg, learns to communicate with the Buggers, and they immediately realize the war was a tragic mistake borne of misunderstanding & the difficulties of inter-species communication.
Ender is literally forgiven by the species he killed.
Technically true, but a bit misleading. The Buggers *started* the conflict by quasi-invading our solar system. At that point they didn't think we were a self-conscious & intelligent species. And they didn't understand
individual consciousness at all. On top of that, the Buggers were far more technically advanced - humanity reverse-engineers the key technologies that make the International Fleet, ansible, and (I believe?) the MD Device possible.
So yeah, Ender is forgiven, but the Buggers started it & regret their badly-handled (mandibled?) first contact.
Everyone says he isn't responsable for the genocide. That he was tricked into it.
He was tricked into it. That's objective true in the book.
Until "The Hive Queen" is published. After that, he becomes "Ender the Xenocide", a loathed historical figure.
Ender isn't scarred physically or psychologically.
Don't think this is supported by the text. Doesn't Ender go into shock for days after learning he used a real MD Device on the real Bugger home planet? He's clearly traumatized, and after he finds the Hive Queen egg, he devotes the rest of his life to helping bring back their species.
How is genocide repudiated in this novel?
How isn't it? The war & attempted xenocide are ultimately a tragedy and the values the books promotes most strongly are understanding and compassion, even among dramatically different forms of life (who were former enemies).