Function solve_rider 

pub(crate) fn solve_rider(
    indexed: &IndexedDocument<'_>,
    path: &BlockPath,
    presentation: &Presentation,
    edited: Edited<'_>,
    sink: &mut CommitBuilder,
) -> Option<Rect>

The solve rider: re-solve the wires the gesture disturbed, and author what that promotes into the same commit.

Scoped to the foreground rather than the whole scope, because re-solving every wire means every wire may move — a cost proportional to the sheet, and geometry churn nobody asked for: one block moving one cell used to rewrite two thirds of a small sheet’s corners.

A gesture that has written nothing has nothing to solve against. Returns the rectangle the gesture disturbed, for the reconstruction that follows the commit.