Options which control which StockLevel rows
StockLevelService.lockStockLevelsForVariants locks.
booleanfalseWhen true, ProductVariants which do not track inventory are locked as well.
Leave it false when the lock protects a saleable stock check, as the order paths do:
an untracked variant has no stock to check, so locking it would only make concurrent
checkouts of that variant wait for each other.
Set it to true when the transaction derives what it writes from the current
stockOnHand, as an absolute stock adjustment does. That read-then-write needs the lock
whether or not the variant tracks inventory, because an admin can set the stockOnHand of
an untracked variant just the same.