POST /v1/workspaces/{id}/move.
The destination only. The profile the workspace is leaving is not sent: the Store already knows it, and a caller that had to name it could name the wrong one - which would either be ignored, making the field a lie, or refused, making a move fail because a listing was a moment stale. The field is spelled owner because that is what a workspace's profile is called everywhere else on this wire, [NewWorkspace] included.