Supercharger v1 and v2 cool passively. The v3 and v4 cables are actively liquid cooled. They’re designed to just stop if the sensors fail.

Maybe, but over billions of charging hours I have not heard of any stories about chargers catching on fire yet. I have to assume that if one of them did catch on fire it would be all over the news, the media is starving for anti-EV stories.

Assuming it's true, then probably the sensors are fail-safe.

But I'm not totally convinced Tesla is going over the cable rating. A lot goes into the rating of a particular cable -- everything from conductor material and size to the insulation around the conductors, proximity of conductors, etc. Not to mention the liquid cooling. It's plausible that supercharger cables are rated for more than 600A.