Oh, I understand now - you're right, OTP sensor data does protect against a real threat model I hadn't considered before:

* A remote attacker gains whatever privilege lets them get to the sensor SPI. * Without OTP calibration, the attacker could reprogram the sensor silently to report a different endstop, keeping the machine awake and the hard-cuts active. * With OTP calibration, this is closed.

So perhaps it is more security-related than I initially thought.

I was more considering the counterfeit part / supply chain / evil maid scenario, where the fact that Apple's sensors are OTP is meaningless (since a replacement sensor doesn't need to be, plus, you could just put a microcontroller pretending to be a sensor in there since there's no actual protection).

Thanks, you made me think again and figure it out!