Take the rate epoch from the slowest stream's frontier, since reading a bucket claims every stream has delivered through it

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"flag"
 	"fmt"
+	"math"
 	"net"
 	"os"
 	"os/signal"
@@ -135,17 +136,20 @@ func (w *rateWindow) at(i int) counterSet {
 	return w.buf[i%len(w.buf)]
 }
 
-// How long the newest epoch may sit still before the wire is taken to have gone
-// quiet. A stamp only advances when a frame arrives, so a frozen epoch means no
-// traffic rather than an unchanged rate.
+// How long the frontier may sit still before the wire is taken to have gone
+// quiet. It only advances when frames arrive on every stream, so a frozen
+// frontier means a stream has stopped delivering rather than an unchanged rate.
 const rateStale = 100 * time.Millisecond
 
-// The newest epoch is still filling, since frames received in it may not have
-// been drained yet, so the rate is read from the one before it.
+// A stamp is only knowable once a worker drains the frame carrying it, so each
+// stream's newest epoch is a frontier: everything the wire delivered to that
+// queue before it has been counted. Reading one bucket across the board takes
+// the one behind the lowest frontier, which every stream has delivered past.
+// The leader's frontier would claim buckets the stragglers are still filling.
 func (d *direction) readRateBucket(now time.Time) {
-	var newest int64
+	newest := int64(math.MaxInt64)
 	for _, r := range d.rxStats {
-		if e := r.newest.Load(); e > newest {
+		if e := r.newest.Load(); e < newest {
 			newest = e
 		}
 	}