Open conflict

When PCs directly oppose each other through violence, subterfuge, sabotage, or whatever—then slow down. A lot.

First, do a temperature check. If things feel heated between the players, then call time out. Check in. Make sure everyone wants to proceed. A little conversation can go a long way towards preventing hurt feelings, resentment, and distrust.

If everyone is on board with the conflict, then give everyone involved a chance to declare their intent. When one PC does something that actively affects another PC or their interests, tell the targeted player what they perceive. Ask what they do in response. If any other PCs are present or involved, ask what they do as well. Figure out what moves are being triggered, and in what order. Very often, someone will end up Interfering.

Use the results of PC actions and player moves to inform what comes next. Keep checking in with the players. Move the spotlight and give other PCs chances to get involved. If someone rolls a 6-, push things to their logical (if unfortunate) conclusion, or interrupt the whole conflict with some unrelated but pressing problem.