Focus time and reading time have always overlapped, so Roomie now knows about books. Search the catalog, add a book, and it lands on one of three shelves: Currently reading, To read and Read. Your Library lives on your profile with a row of covers for what you are reading now and a See all link; other people's profiles show theirs too.
Progress is logged the way you actually read: by page or by percent, with quick chips for the usual jumps and a "finished" toggle when you close the back cover. Each book can belong to a focus area, so a Reading area shows its shelf alongside its sessions.
When you finish a session, attach the book and how far you got. The post then carries a small row, "Read 24 pages of Atomic Habits · 61%", with a thin progress bar while the book is still in progress. Grouped posts sum the pages across the whole run, so a morning of three sessions reads as one line rather than three.