Hotfix release.
Fixed
- Kobo no longer shows "Download" again for books you already have after a sync hiccup. When a Kobo has to re-sync from scratch (after a firmware update, an interrupted sync, or a lost sync token), Calibre-Web now remembers exactly what each reader already received and skips re-sending unchanged books, so the reader keeps its downloaded copies and your reading position. A real change to a book is still delivered normally.
Verified end to end on hardware: a forced full re-sync of a 218-book library re-sent nothing, flipped nothing, and left every annotation and reading position untouched; a genuine book change was still delivered as exactly one update.