Back when I was an active scene runner/prp person for vampire and werewolf and law, I just asked for the people signed up (or who'd requested I run a story for them) to privately disclose any "no go" areas/themes for them. Then I could privately advise them to either not participate or if possible alter some details that I knew about in advance.
To be honest, I think a lot of players like to be surprised/to feel unscripted/have to think on their feet. Unlike a published prewritten article, a plot is something that can change/move due to the dynamics of the people in it (in theory anyway). If you have to give a rundown summary that removes some of that element. Or it desensitized people to content warnings over time. I know some problematic people who will indeed file complaints/scream at people over certain content that regularly signed up for scenes in which warnings of a general but accurate sort were given. They had lots of friends going and didn't want to not sign up, and then targeted the runner for their abuse. Now the same thing could be said of privately asking, but I had a lot more success with it, both in being able to tailor the scene without anyone's knowledge into something enjoyable for everyone, including me--but also in feeling more entitled to then boot/remove a player being a dick afterwards and protect other players vs. needing to focus all my attention on a player freaking out after they'd been given a opportunity to proactively disclose their Do Not Go areas.
Yes, that is cold to some extent. But a) I no longer tolerated people using MUSHing as their therapy/other players as their whipping boys/girls due to other issues and b) got sick of the squeaky wheel/needy player in the scene in progress slowing things down/wasting the time of other players that were GGG (Good, Giving, and Game). I'm a nice, considerate person in RL and most of the time in game. But when it comes to running a scene or plot, I prefer to protect the experience of the quiet people too, and respect everyone's time by avoiding derailing ooc behavior.
I think as long as the runner has given each person ample opportunity to disclose their NOPE areas, then the responsibility lies on the triggered person to quickly and with minimal ooc disruption exit the scene. And I agree with Coin, that it also is very annoying when someone decides to roll into a sphere that is obviously not going to be something they can thematically handle, and then proceeds to bitch/try to change/vomit their discontent all over people who are playing canon theme.