diff --git a/harness/main.go b/harness/main.go
index e9d2afe..3152f09 100644
--- a/harness/main.go
+++ b/harness/main.go
@@ -1,6 +1,6 @@
-// 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.
+// Runs cabletest until interrupted or for -for, 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
@@ -35,7 +35,7 @@ const (
 )
 
 func main() {
-	runFor := flag.Duration("for", 15*time.Second, "how long to let cabletest run")
+	runFor := flag.Duration("for", 0, "how long to let cabletest run; 0 runs until interrupted")
 	at := flag.String("at", "", "offsets to capture the panel at, comma separated, e.g. 3s,10s")
 	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()
@@ -49,6 +49,11 @@ func main() {
 
 	var err error
 	if *fuzzN > 0 {
+		if *runFor <= 0 {
+			restoreTerm()
+			fmt.Fprintln(os.Stderr, "fuzz needs a bounded -for")
+			os.Exit(1)
+		}
 		err = fuzz(*fuzzN, *runFor, flag.Args())
 	} else {
 		err = run(*runFor, *at, os.Stdout, flag.Args())
@@ -122,7 +127,7 @@ func parseShots(s string, runFor time.Duration) ([]time.Duration, error) {
 		if err != nil {
 			return nil, fmt.Errorf("bad offset %q: %w", f, err)
 		}
-		if d < 0 || d >= runFor {
+		if d < 0 || (runFor > 0 && d >= runFor) {
 			return nil, fmt.Errorf("offset %s falls outside the %s run", d, runFor)
 		}
 		out = append(out, d)
@@ -189,12 +194,16 @@ func run(runFor time.Duration, at string, out io.Writer, args []string) error {
 		fmt.Printf("captured %s\n", name)
 	}
 
+	var expire <-chan time.Time
+	if runFor > 0 {
+		expire = time.After(time.Until(start.Add(runFor)))
+	}
 	select {
 	case err := <-done:
 		return exited(start, err)
 	case <-sigs:
 		return interrupted(start, pgid, done)
-	case <-time.After(time.Until(start.Add(runFor))):
+	case <-expire:
 	}
 	return stop(pgid, done)
 }
diff --git a/harness/stream.go b/harness/stream.go
index 349087d..af1e81f 100644
--- a/harness/stream.go
+++ b/harness/stream.go
@@ -24,23 +24,31 @@ const page = `<!doctype html>
 <script>
 (async () => {
   const cv = document.querySelector('canvas'), g = cv.getContext('2d');
-  const rd = (await fetch('frames')).body.getReader();
-  let buf = new Uint8Array(0);
   for (;;) {
-    const {value, done} = await rd.read();
-    if (done) return;
-    const b = new Uint8Array(buf.length + value.length);
-    b.set(buf); b.set(value, buf.length); buf = b;
-    for (;;) {
-      if (buf.length < 12) break;
-      const dv = new DataView(buf.buffer, buf.byteOffset);
-      const x = dv.getUint32(0, true), y = dv.getUint32(4, true), n = dv.getUint32(8, true);
-      if (buf.length < 12 + n) break;
-      const bmp = await createImageBitmap(new Blob([buf.slice(12, 12 + n)], {type: 'image/png'}));
-      if (x === 0 && y === 0 && cv.width !== bmp.width) { cv.width = bmp.width; cv.height = bmp.height; }
-      g.drawImage(bmp, x, y);
-      buf = buf.slice(12 + n);
-    }
+    try {
+      const res = await fetch('frames');
+      if (res.ok) {
+        const rd = res.body.getReader();
+        let buf = new Uint8Array(0);
+        for (;;) {
+          const {value, done} = await rd.read();
+          if (done) break;
+          const b = new Uint8Array(buf.length + value.length);
+          b.set(buf); b.set(value, buf.length); buf = b;
+          for (;;) {
+            if (buf.length < 12) break;
+            const dv = new DataView(buf.buffer, buf.byteOffset);
+            const x = dv.getUint32(0, true), y = dv.getUint32(4, true), n = dv.getUint32(8, true);
+            if (buf.length < 12 + n) break;
+            const bmp = await createImageBitmap(new Blob([buf.slice(12, 12 + n)], {type: 'image/png'}));
+            if (x === 0 && y === 0 && cv.width !== bmp.width) { cv.width = bmp.width; cv.height = bmp.height; }
+            g.drawImage(bmp, x, y);
+            buf = buf.slice(12 + n);
+          }
+        }
+      }
+    } catch (e) {}
+    await new Promise(r => setTimeout(r, 1000));
   }
 })();
 </script>