Every `move_to` guaranteed its destination's parent with a `MKCOL` for
each ancestor down from the account root, and a trash folder under a
library root several levels deep meant three round trips answering
`405 Method Not Allowed` before the one `MOVE` that did anything — for
every image of a delete, on a connection built for that job.
The backend now records the collections it has confirmed exist and asks
about each once. It lives for one job, so a folder another client removes
mid-batch is the one case this misses, and the `MOVE` then reports the
`409` rather than hiding it.
dtourolle
73845d8a77