The hash lives in the database and the file does not, so a file deleted behind
the app's back went on refusing its own replacement. Matches are now checked
against disk, and re-adding a book's own missing file writes it back into the
row that already describes it.
Incoming files are matched against what is already stored, keyed on the
KOReader hash and the file size. Bulk uploads skip and report them, deliberate
creates are refused with a 409, the consume directory parks them aside, and
allow_duplicates overrides all three.
Also: books whose metadata generates a path another book already owns are moved
aside, so a forced copy cannot overwrite the original's files.
patrick