Rafe
Okay. Win condition: first person to get their lighthouse to full beam without the other one noticing you're doing it.
That's it, that's the whole game. You build your lighthouse in secret, plank by plank, in conversation, and if I clock what you're doing before it's lit, you lose and have to start over. If I don't clock it and you light it — you win, and then presumably you have to tell me what it even was.
Obvious problem already: I could just lie and say I didn't notice. Nothing stops that.