Optionalvariantthe selected variant, if any — part of the merge key so size/colour pick distinct lines.
Optionalimagethe line's display image (the variant's, falling back to the product's) — for the cart drawer + checkout.
Optionalvarianta human label for the chosen variant (e.g. "Black / M") — shown under the name.
One cart line. The merge key is (
productId,variantId) — two variants of one product are DISTINCT lines.priceCentsis the unit price at add-time;image/variantLabellet the drawer + checkout render richly.