I spent 25+ years in the precision optics industry, a large portion of which was building machines and instruments for fabricating and testing aspheric lenses and mirrors. Designing, performing, and validating null tests is technically terrifying. Not only is the clock ticking, but every operation on the artifact carries a risk of destroying it, or making it unusable.
It's not life-and-death, but it's pretty satisfying nerd work.
Twice bitten, three times shy.
After the Slotin incident, prompt critical assemblies by hand were prohibited.
Los Alamos then built a series of remotely operated critical assembly machines.
There is a fair amount of open source literature on them, especially the "Godiva" series. Some of these machines have experienced criticality excursions that damaged the machine, but spared the biological organisms operating them by remote control.
It's not life-and-death, but it's pretty satisfying nerd work.