Compose + Match (per-frame)

Composite source over destination via a mask, with a per-frame correction so the inserted region matches the plate. 'Grade match (surround)' estimates the VAE/grading drift from the unchanged area outside the mask (where source & destination share content) and applies it to the source inside the mask -- fixes seam luminance/contrast without changing the element's colors. 'Color match (palette)' is the distribution-based color-matcher approach. 'temporal_anchor' (iterative video) re-matches each iteration's element to the previous iteration's corrected tail so VAE drift can't compound.