UnexpectedReturnLine covers two opposite conditions, so a race reports as a permanent refusal

ReceiveGoods throws UnexpectedReturnLine::notOpenToGoods() when the return is no longer open to goods. That is the same exception class raised for a line the return genuinely does not cover.

The two conditions are opposites:

• Unauthorised goods — permanent. No quantity on this return can be raised to make that line fit; the parcel needs a new request.
• No longer open to goods — a race. The return expired, or was inspected, between a page rendering and a button being pressed. The line is plainly covered; the timing is wrong.

A consumer has to tell them apart to answer correctly, and with one class it cannot. The Filament package's amendability() currently labels the race with the permanent message — "no quantity on this return can be raised to make it fit" — for a line the return does cover. The operator advice that falls out happens to be right (start a new request), but it is right by coincidence of class rather than by design, and the explanation given is false.

This is the same shape recorded against Checkout in the migration plan: one exception class published for two opposite conditions, forcing every downstream surface to rebuild the distinction from a message string. Checkout's consumer had to match on the domain's own message factory to answer 409 vs 423. The fix belongs here rather than in each surface — publish two cases.

Note that -api packages are landing against this module now, and an HTTP status is exactly the distinction that cannot be made from one class: unauthorised goods is a 422, a lost race is a 409.

Start at ReceiveGoods and UnexpectedReturnLine::notOpenToGoods(), then trace the Filament package's amendability() handling and the migration-plan reference to Checkout. Identify how the domain currently exposes the two conditions and verify the -api consumers can distinguish unauthorised goods from a lost race without parsing messages; done means each condition has a distinct public case and the existing consumers can map them correctly.