null on a finished session — there is no live cart to price.
active while the cart can still be edited. expired (past its TTL) or
converted (handed off to checkout) once the session is finished — those
come back as a normal 200 with a zeroed summary, not an error, so a badge
can render a zero without a try/catch.
Cart total in minor units, or 0 on a finished session.
Sum of the line-item quantities — 1 stand + 2 notebooks + 1 keyboard is
4, not 3. Named for what it counts because itemCount elsewhere in
Throttle (the cart.abandoned payload) means the number of distinct lines.
The badge-sized read: what a storefront header needs to draw a cart count, and nothing more. No line items, no addresses, no buyer email or notes.