omit last unused span

cmd/kv-write-canary/main.go

@@ -73,7 +73,11 @@ func poll(ctx context.Context, client *valkey.Client) Poll {
 		waitSuccess(ctx, client, func(s string) {
 			writes = append(writes, s)
 		})
-		spans = append(spans, [2]time.Time{time.Now(), time.Now()})
+		now := time.Now()
+		spans = append(spans, [2]time.Time{now, now})
+	}
+	if last := spans[len(spans)-1]; last[1] == last[0] {
+		spans = spans[:len(spans)-1]
 	}
 	return Poll{Spans: spans, Writes: writes}
 }