The request blocks until the desktop finishes

The map layer comes out of a desktop GIS app, through File, Export, and nothing else.

You wrap the export in an exec handler at /layers/[name]. It POSTs window/search for the app by title, window/focus on the id that comes back, keyboard/key with ["ctrl+e"], then loops: input/wait for two seconds, window/search for the Export complete dialog, again. When the dialog appears the handler closes it, reads the file the app just wrote from the container's disk, and returns it. // @timeout 5m sits above the function, because the request takes as long as the render does.

The client's portal now fetches a fresh layer with a GET. The app still thinks a person clicked Export.

The request blocks until the desktop finishes, and that is the whole integration.