fix: calculate conservative SLO percentiles

server/observability/slo_test.go

@@ -25,3 +25,9 @@ func TestEvaluateSLODoesNotInventFailureForEmptyOptionalWindows(t *testing.T) {
 		t.Fatalf("empty window violations = %+v", violations)
 	}
 }
+
+func TestPercentileUsesConservativeNearestRankForSmallWindows(t *testing.T) {
+	if got := percentile([]time.Duration{time.Millisecond, 101 * time.Millisecond}, .95); got != 101*time.Millisecond {
+		t.Fatalf("p95 underreported small window: %s", got)
+	}
+}