Import skipped copying when a file of the same size already had the
name, so a damaged copy the size of the good one survived an add that
said "Added". add() now tells import to replace it: anything with the
match's name there wasn't a readable copy of it. add() also waits for the
first listing, which would otherwise publish over the add's newer one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>