Function build_grid_paged 

pub fn build_grid_paged(
    model: &Model,
    measure: MeasureId,
    snapshot: &Snapshot,
    page_idx: &[usize],
) -> Grid

Like build_grid but pins each extra (page) dimension to the item at the given index (clamped). page_idx[i] selects the item for the i-th extra dimension (categories beyond the first two); a missing/short entry defaults to 0. Enables paging through a 3+ dimensional measure.