What "context"? If it's coming from the player's input, then the LLM isn't spoiling anything.

e.g. let's say an important character dies in your game but that hasn't happened yet in this point in the story. You're talking to some NPC. That NPC can't possibly spoil that that character is going to die because the developer wouldn't feed that in as context. The NPC doesn't "know" the character is going to die. You, as the player, might be able to convince the NPC that that will happen and it might respond accordingly, but it won't just randomly divulge that by accident.