A write-off destroys the reserved part of an expired lot

Stock.write_off_expired in src/stockpile/stock.py answers one question:

which of the expired lots' quantity can go away? The rule, as documented on

the method:

• a write-off removes only what is free — quantity nobody is holding;
• committed quantity is already off the shelf, so it is never touched;
• reserved quantity is somebody's claim, so it is never touched: the lot

stays alive while a claim still rides on it, because the warehouse has to

be able to commit the order it already promised.

The defect zeroes the reserved quantity along with the free one. An order that

is holding stock on a lot that has since expired is left with nothing to

commit — no error at the write-off, just a claim that no longer corresponds to

anything.

The repository's own suite is green on the pinned commit, because it only ever

writes off an expired lot that carries no reservation, for which keeping the

reserved part and destroying it are the same thing. The defect only shows up

when a reservation is still riding on a lot that has expired.