The edge request-latency histogram records seconds but used the OTel SDK's
default millisecond-calibrated bucket boundaries (first boundary 5), so every
sub-5s request fell into one bucket and histogram_quantile(0.99) interpolated
to ~4.95s for every message type — regardless of the real (millisecond)
latency. That tripped the >1s "Gateway request latency p99 high" alert on
essentially every request, flapping fire/resolve on each app open (seen on the
test and prod contours).
Set explicit second-scale bucket boundaries (0.005 … 10s) straddling the 1s SLO
so the p99 reflects real latency and the alert fires only on genuine slowness.
Regression test asserts the histogram carries a sub-second boundary.
Ilia Denisov