Function row_at 

pub fn row_at(
    area: Rect,
    wizard: &Wizard,
    column: u16,
    row: u16,
) -> Option<usize>

Which selectable row, if any, sits under a point in the window.

This rebuilds the layout the last frame used rather than remembering it. A stored layout would make drawing a state change, and the wizard’s one rule is that a render never moves anything; rebuilding costs a screenful of lines on a click, which is not a cost worth trading that rule for.