MonitorBar

The story

A native menu bar app built for one monitor, the MSI Optix MAG342CQR. The monitor has no USB port, so MSI's own software cannot reach it. MonitorBar talks to it over DDC/CI on the DisplayPort cable instead, through Apple's private IOAVService API on Apple silicon. Most of the work was learning how the monitor misbehaves. It drops the first write it receives, so every request goes out twice. It also drops a setting that arrives while it is still applying the last one, and reports success anyway, so each write is read back and resent until the monitor agrees. Probing found 45 VCP codes, four of them undocumented, which now sit under an Experimental panel. The lesson: when hardware says yes, check.