Function optimize_linear_gradient 

pub fn optimize_linear_gradient(
    prim_rect: &mut LayoutRect,
    tile_size: &mut LayoutSize,
    tile_spacing: LayoutSize,
    clip_rect: &LayoutRect,
    start: &mut LayoutPoint,
    end: &mut LayoutPoint,
)

Perform a few optimizations to the gradient that are relevant to scene building.

Mutates prim_rect, tile_size, start, end to bake in the simplifications (repeated-tile collapse, equivalent-to-stretching on either axis, clip-induced offsets). Decomposition into per-segment quads is no longer done here – the caller emits a single LinearGradient prim and prepare-time runs decompose_axis_aligned_gradient against the snapped prim_rect when the gradient is eligible. Doing the decomposition at frame-build keeps adjacent segments phase-aligned with the snapped outer prim, even when the frame-time snap pass nudges the outer rect.