1. If the UHF comm link fails, the reciever issues an output that interrupts the MCU initiating a Stop procedure. ( This takes care when the tractor just runs out of the communication range or looses signal someother way)
Should be: the controller will only allow movement when the signal is present. (example trigger the watchdog with an and of signal present and the other reason(s))

2. An independent electronic watchdog ( powered by a seperate battery and not the tractor battery )coupled with a bit from the MCU keeps a relay from dropping off when the tractor is moving. The moment this relay drops, the throttle circuit goes dead and defaults mechanically to idle and the spring loaded clutch actuator disengages and a similiar spring loaded brake actuator clamps.
again it should not be interrupt movement when bad, it should be allow movement when OK.

Mechanisms made to say 'bad', if they fail all is allowed. Mechanisms made to say 'good' when they fail all is disabled.

Erik