Failure SimulatorDeterministic hostile inventory test
Last-unit race test
Opening quantity 1, one sale, then a duplicate sale webhook with the same idempotency key.
REMOTE OUTCOMES
Fail safely; never fake green.
ShopifyVERIFIED SYNCEDVerified remote qty 0
eBayDEGRADEDNo verified remote quantity
StockXPROCESSINGNo verified remote quantity
PoshmarkMANUAL REQUIREDNo verified remote quantity