Does BookyAI keep previous versions of my chapters? How do I restore one?

Yes, since v1.8.3. BookyAI automatically saves a snapshot of a chapter BEFORE every regeneration and before edits (at most one per hour, so routine typing doesn't flood the history). The last 10 snapshots per chapter are kept, as plain text files inside your book's folder. To restore: open the chapter in the editor and click "Versions" — you'll see each snapshot with its date and word count; click Restore on the one you want. The current text is snapshotted first, so you can always change your mind and go back again.