Before a Shared Idea Becomes a Shared Commitment

A cofounder suggests trying a new direction. One person hears an exciting first step; the other may hear an unspoken promise to build, maintain, and own it.

What would you want agreed before either person begins? For example: who shapes the scope, what needs to stay stable, and when you’ll review or stop the trial. What wording makes it easier to say yes, reshape the idea, or decline—without turning the answer into a test of commitment?