Crash detection.
I keep a little printed garbage can next to the printer for intro lines, supports, and other wasted plastic. Every now and then it gets moved and ends up under the x-axis stepper. With the old MK3 when this happened before a print, the x-axis would come down, hit the top of the can and stall-out the steppers. This forced a z-axis recalibration, but no big deal.
It happened to my MK4 today. The x-gantry hit the can and the left-side of the printer started climbing up. The spool came off the spool holder and rolled away. I caught it immediately, freed the can and put the printer back on the desk. The dang thing just continued on happily like nothing was wrong.
It was sort of scary, but I gotta say, I'm kinda impressed it worked. Still, I think it shows that crash detection needs to make a comeback, or the z-axis check needs needs some more work.
https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/3191
When someone asks you if you're a god, you say, "YES!"