Constant SILENT_FLUSHES_BEFORE_DEGRADED 

const SILENT_FLUSHES_BEFORE_DEGRADED: u32 = 5;

Consecutive silent flushes before a pair that used to deliver is called dead.

Flushes are one second apart. Three was measured to be too few: it fired six times during healthy operation, once per flush, because a burst of mints can outrun its replies for a couple of seconds without anything being wrong. Five keeps detection well inside the fifteen-second budget – the dead leg reads exactly zero from t+5s onward while its siblings keep returning.