Function build_grid_pivoted 

pub fn build_grid_pivoted(
    model: &Model,
    measure: MeasureId,
    snapshot: &Snapshot,
    page_idx: &[usize],
    axis_order: Option<&[CategoryId]>,
    filters: &[Filter],
) -> Grid

The most general grid builder. axis_order, when Some, is a permutation of the measure’s categories that sets which category is on rows (first), columns (second), and pages (rest) — this is how the UI pivots without touching formulas. None uses the measure’s natural category order. filters restricts which items of a category are shown (presentation only; unlisted categories show all items).