> the script had a RM /$var - had the var been empty somehow, it could've deleted the os

I had something almost identical that was missed by Auto Mode a couple of days ago, but thankfully not with the same failure mode. It was copying files into another directory, but $var was never set by the script Claude wrote. So instead of copying across the few files it had intended to, for a few minutes Claude was happily recursively copying from the root of the filesystem into this folder. Luckily the operation timed out while I was away from computer, and I came back to a horrified Claude stating "I need to be honest here".