Why the Desktop Rule demands three windows
Two panes is a book. Three panes is a desk. The category fails if the third leaf is only a bigger video.
The Trifoldable Standard is blunt about this. A pocket laptop must run three windows natively: a document, a reference, and a conversation. If the third leaf only mirrors the second, you have bought a tablet with extra hinge.
Samsung's DeX and Huawei's split stack both pass when the image is configured. They fail when a banking app seizes the canvas and refuses to share. Certification of the phone is not certification of the app. IT should keep a deny-list of full-screen takers.
Write it into the requisition. If the vendor cannot show mail, a spreadsheet, and a call bubble at once on a shipping build, the badge does not leave the drawer.