Stream the panel as masked png deltas and seqlock the scanout reads

harness/main.go

@@ -1,5 +1,6 @@
-// Runs cabletest for a fixed time and dumps the panel to png, since the machine
-// with the display on it is not the machine looking at it.
+// Runs cabletest for a fixed time, dumps the panel to png, and streams it as
+// png deltas on :8080, since the machine with the display on it is not the
+// machine looking at it.
 //
 //	sudo go run ./harness -for 20s -at 3s,15s -- -a enp1s0f0np0 -b enp1s0f1np1
 package main
@@ -37,6 +38,11 @@ func main() {
 	fuzzN := flag.Int("fuzz", 0, "repeat the whole lifecycle this many times; full output only for runs that fail or log module events")
 	flag.Parse()
 
+	if err := serveStream(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
 	var err error
 	if *fuzzN > 0 {
 		err = fuzz(*fuzzN, *runFor, flag.Args())