Add ArtPoll backoff when hearing polls from other sources

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

discovery.go

@@ -32,6 +32,8 @@ type Discovery struct {
 	pollTargets   []*net.UDPAddr
 	done          chan struct{}
 	onChange      func(*Node)
+	lastPollHeard time.Time
+	pollMu        sync.Mutex
 }
 
 func NewDiscovery(sender *Sender, shortName, longName string, inputUnivs, outputUnivs []Universe, pollTargets []*net.UDPAddr) *Discovery {
@@ -86,6 +88,14 @@ func (d *Discovery) pollLoop() {
 }
 
 func (d *Discovery) sendPolls() {
+	d.pollMu.Lock()
+	lastHeard := d.lastPollHeard
+	d.pollMu.Unlock()
+
+	if time.Since(lastHeard) < 15*time.Second {
+		return
+	}
+
 	for _, target := range d.pollTargets {
 		d.sender.SendPoll(target)
 	}
@@ -145,6 +155,13 @@ func (d *Discovery) HandlePollReply(src *net.UDPAddr, pkt *PollReplyPacket) {
 }
 
 func (d *Discovery) HandlePoll(src *net.UDPAddr) {
+	localIP := net.IP(d.localIP[:])
+	if !src.IP.Equal(localIP) {
+		d.pollMu.Lock()
+		d.lastPollHeard = time.Now()
+		d.pollMu.Unlock()
+	}
+
 	if d.receiver == nil {
 		return
 	}