Single item within a checkout — one bookable PATH. A listing booked through two overlapping packages (or a package plus its own standalone row) in one order is one item per path, each with its own quantity and price.
listingId: number
quantity: number
unitPrice: number
slug: string
name: string
optional
packageGroupId: number | undefined
The package this line books through (absent = a standalone/child line).
Signed per line as the item's k/r edge tag and stamped onto the line's
booking row.
optional
purchaseUnit: PurchaseUnit | undefined
What one purchased unit buys. Absent = plain tickets. A months unit names the term the provider checkout and the order summary state — ×3 beside a "(1 Month)" plan buys three months of one site, not three sites. Display only: fulfilment reads its own facts.