Loading accepted a file entry whose hashes list was empty. check and
fetch then failed the file as a hash mismatch, and freshen left it out
of the rewritten manifest without a word.
NewManifestFromReader now refuses such an entry, naming its path, after
checking the path itself. freshen's addExistingToBuilder returns an
error for an entry with no hash instead of skipping it. The file entry
table in docs/FORMAT.md says readers reject an entry with none.
Model: opus-5-5
sneak