A browser pretending to be a panel: it polls the real hub and draws with the firmware's own code, so a metric can be designed before any board exists.
Any MAC works. A new one registers itself on first poll and shows a claim code, exactly like a freshly flashed board. Use a second MAC to preview a second slot.
no poll yet
The payload must stay under 768 bytes — the firmware's JSON buffer. Over it the real device parses nothing and freezes on its last frame.