I don't know? Trust, I guess? i.e, I could be the gamemaster and give everyone prompts like an introduction to the story and then let them know that every day they get 1 message to send, they cannot control the actions of others in their message, only their own actions. They can use their messages to describe their surroundings, on the first day, users will decide the contents of Root's manor and the contents cannot be retconned, if it ends up becoming a hello neighbour house then so be it. I.e Hagon could say "Hagon stumbles into Root's hidden sex chamber, it's full of rotting carcasses and jartycucks." and I could say "Soygoy walks his way into the living room. There is a flatscreen TV hanging on the red fabric walls. The floor is wooden, but on top if it is a tapestry rug depicting Root's time as admin of soyjak.party. 3 little chuddies is playing on the TV" etc.
You must talk about yourself in the third person and being the gamemaster, I decide the overall narrative for every day. So a player cannot say "Sloppa murders Soygoy" so I suppose there will have to be some rules from the gamemaster about what you can and can't do in your 1 message per day. Everyone gets 1 message again after a new post from the gamemaster, and maybe the gamemaster can't play, just to make things easier.
Gamemaster can ask people privately to be the murderer and ask them how they'll do it and who they'll kill and we can do murder mystery, ie "Hagon asks ILoveVesna a question about the knife 'Do you remember where this knife came from?'" and ILoveVesna could respond "ILoveVesna ponders on Hagon's question, 'Possibly the kitchen. Only place I can think of'" etc.