OptionalorderDefaults to sess:<sessionId>:<n>. A caller-supplied id must carry the session prefix, so
session orders can never collide with main-lane orderIds by construction.
The full CREDIT price; drawn from spendable only (promo is main-lane).
OptionalexpiresAt?: numberEpoch ms a temporary grant lapses; required for temporary, forbidden otherwise.
Sale split, spend's rule: shares of the post-fee net, summing to exactly 10000 bps.
One purchase offered to the lane. The economy service builds this from its own catalog and routing, so a malformed shape (non-CREDIT price, unknown kind, shares off 10000 bps) throws a fault rather than rejecting — a bad one is a wiring bug, not a buyer outcome.