I sort of like the idea of a general agreement that people will try to move a discussion that's triggery when asked. Not sure the formalization of a "safe word" changes it much, and given the communications issues (making sure people know it, whatever), it seems like relying on "hey that's sort of upsetting to me" would probably be enough maybe? But I sort of like the idea of a general understanding that people will try to handle triggery topics politely and gracefully. The meltdown thing is sort of separate from that, I think. And I'm not really sure what to do apart from "hey guys everyone here is vulnerable please be careful".