An integration could put a file into a folder by id but could not see,
make or arrange the folders themselves, so mirroring a directory tree
into ProjectSend was impossible over the API. The hosted AI connector
already creates, lists and shares folders.
GET /folders polls like every list (updated_since, cursor) and filters
on parent_id, top_level and search. Each folder carries its ancestors
and a display path, trimmed for a client-scoped token to the folders it
may see (BreadcrumbBuilder::visible's rule), worked out for a whole page
in two queries by FolderTrails.
POST /folders returns an existing folder of the same name in the same
place with a 200 rather than making a second one, so a retried request
is safe. PATCH renames and moves. DELETE refuses a non-empty folder with
409 unless content_action=cascade_delete is sent, and then asks
UndeletableFiles exactly as the web does. Sharing goes through
FolderSharing.
Every write uses the web's policy, scope and FolderService, and asks
Folder::uploadableBy for every parent it writes, creation included.
Public state stays web-only: the resource reports `public`, nothing here
changes it. A file's `folder` now carries `parent_id` as well.
ignacionelson