Perhaps the Sphere-1 was the first which is what its wiki article asserts
https://en.wikipedia.org/wiki/Sphere_1 using two keys wired in series to provide a hard reset...
ASIDE: This machine is the one famously used by Scott Adams before he used the TRS-80 to write Adventureland. This is not as the story goes the earliest adventure game for home micros but, the port of the classic ADVENT for the HeathKit H8 was which was in August 1978, a few months earlier -
https://bluerenga.blog/tag/adventureland/?order=ASC