Reads the newest relay backlog-age gauge sample and fires when it is at or past ageMs, or
returns null when no sample is buffered or the newest is under the bound. Only the newest
sample matters — the gauge pair rides each relay run, so an old high reading followed by a
fresh low one means the backlog drained. pending comes from the newest depth gauge.
Reads the newest relay backlog-age gauge sample and fires when it is at or past
ageMs, or returns null when no sample is buffered or the newest is under the bound. Only the newest sample matters — the gauge pair rides each relay run, so an old high reading followed by a fresh low one means the backlog drained.pendingcomes from the newest depth gauge.