Push the new origin into the sample ring so a reset cannot underflow the totals

main.go

@@ -263,11 +263,13 @@ func (d *direction) snapshot() sample {
 }
 
 // Counters keep climbing in the workers, so resetting just moves the origin
-// everything is measured from. Rates are deliberately left running, since they
-// are instantaneous and would only blink to zero and back.
+// everything is measured from. Rates and the rolling error window are about now
+// rather than since the reset, so they keep running; the origin goes into the
+// ring so the newest bucket never sits behind it.
 func (d *direction) reset() {
 	d.mu.Lock()
 	d.base = d.capture(time.Now())
+	d.win.push(d.base)
 	d.mu.Unlock()
 
 	d.heldFrames = heldValue{}