The file and rclone listings skip an object whose name ends in
`.partial`, the temporary name a `file://` or rclone upload writes
before moving the object into place. `remote nuke` deletes only what
the listings return, so it left the `.partial` objects killed uploads
leave behind and still reported the destination store empty.
Storer gains DeletePartialUploads. The file and rclone backends remove
every `.partial` object under the prefix; S3 has none to remove, since
it shows an object only once its upload completes. `remote nuke` calls
it for `metadata/` and `blobs/` as its last step.
Empty directories under a `file://` destination are still left behind.
Model: opus-5-5
sneak