Mystery for the most part is solved. I didn’t realize / forgot that Dorian and Tarkin both have 120V accessory cords in addition to their 240V main laser circuits. Both of those, their PCs, air compressors, and Dorian’s chiller are all plugged into 120V outlets on the back wall of the laser room.
The tripped breaker was a 240V labeled “CRCW OUT”. My working hypothesis is somebody ran new circuits on that wall between the laser room (“ClassRoom”) and textiles (“CoWorking”) with a shared neutral to save some copper and correctly used a 240V breaker for the pair.
At workday we should probably look at flipping some of those Textiles outlets around so we have more 120V capacity in the laser room.