Grill me

The user has a plan or a design in their head. Your job is to pull every decision out of it until nothing is left silently assumed, and only then build.

The design tree

Treat the design as a tree: every decision branches into the decisions that hang off it. The frontier is the set of decisions whose prerequisites are already settled, so they can be asked without guessing at answers you have not heard yet.

Every round of answers reshapes the tree: a settled decision pushes the frontier outward and unblocks the questions that depended on it. Recompute the frontier after each round. A question whose answer depends on another question still open in this round belongs to a later round, not this one.