The panel, its renderer and the sink between them.

rest_for_one, because each of these holds something belonging to the one before it: the sink draws through EInk, and the renderer is given the sink's pid — Emerge requires a live local process for a headless target and will not take a name. A sink that restarts would otherwise leave the renderer rendering into a dead process, which fails silently at the point where frames simply stop arriving.

On the host EInk is absent, so frames are rendered and go nowhere, which is what makes a screen previewable without hardware.