While I understand the problem of the OP, putting a trigger warning doesn't seem like a good idea.

As said above, we are not sure that it is a viable solution. But in general, I'm also afraid that this kind of request will make a game that is already too consensual even more sterile. By always wanting to spare the audience, we end up preventing the producers from thinking outside the box. And thus to produce scenes worthy of being retained.

I repeat myself: I understand very well the concern of the OP, and I do not minimize his problem at all. I would even agree with him if we could see the scene from start to finish (which is not the case IG). But as it is, I think we should be satisfied with the warning triggers already available in the game, without asking for more.

Finally: a small adjustment is possible when it has no impact on the game experience of the majority (example of the "sage" icon). On the other hand, putting a trigger warning at this precise place would be disturbing for the potential spoiler, and it doesn't seem justifiable to me to privilege a minority to the detriment of the majority's experience. Even if the bias may seem a bit harsh, it is impossible to take into account everyone's traumas, sensitivities and particularities.