The expected success table holds when the four requests enter the shared
pool together. On a loaded runner they are admitted tens of milliseconds
apart, the slot lifetimes overlap differently and the pool overflows
while a short request is still resident. The decode failure aborts every
slot, so a request the table marks as successful comes back with the
context error instead of its generation.
Such a request now passes on that error too, while any other status, a
different error or a truncated generation still fails the test.