Both death rows killed after a fixed sleep, so under load the kill could
land before the call was dispatched. The bus then reports not-dispatched
and MutationCertainty::None, which is correct -- the participant never
received anything -- while the test demanded unknown. A full-workspace
run caught it: "left: None, right: None" at the certainty assertion.
kill_once_it_is_working polls the victim's own Worker.Status until it is
provably inside the operation before killing: the agent until it is
Preparing with an active request id, the world until it has recorded the
batch, which the arena does before its injected delay. Dispatch has then
demonstrably happened and unknown is the only correct certainty.
The wall-clock boundedness assertions are gone with them. The suite's
own `within` is the bound, and the victim is five seconds slow against
its twenty, so returning at all is the claim.
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