Fix web OTA upload and isolate OTA sessions across firmware and goTool.

Split ESP-NOW into core/master/slave modules, block non-OTA UART traffic during updates, and hold the host serial port exclusively so dashboard polling cannot interleave with firmware uploads.

Co-authored-by: Cursor <cursoragent@cursor.com>

goTool/dashboard.go

@@ -101,7 +101,7 @@ func (h *wsHub) setState(st DashboardState) {
 		return
 	}
 	for _, c := range conns {
-		_ = c.WriteMessage(websocket.TextMessage, data)
+		h.writeJSON(c, data)
 	}
 }
 
@@ -112,7 +112,7 @@ func (h *wsHub) register(c *websocket.Conn) {
 	h.mu.Unlock()
 
 	if data, err := json.Marshal(snap); err == nil {
-		_ = c.WriteMessage(websocket.TextMessage, data)
+		h.writeJSON(c, data)
 	}
 }
 
@@ -122,6 +122,30 @@ func (h *wsHub) unregister(c *websocket.Conn) {
 	h.mu.Unlock()
 }
 
+// writeJSON sends to one client; removes it on error or panic (closed connection).
+func (h *wsHub) writeJSON(c *websocket.Conn, data []byte) {
+	defer func() {
+		if recover() != nil {
+			h.unregister(c)
+		}
+	}()
+	if err := c.WriteMessage(websocket.TextMessage, data); err != nil {
+		h.unregister(c)
+	}
+}
+
+func (h *wsHub) broadcastJSON(data []byte) {
+	h.mu.RLock()
+	conns := make([]*websocket.Conn, 0, len(h.clients))
+	for c := range h.clients {
+		conns = append(conns, c)
+	}
+	h.mu.RUnlock()
+	for _, c := range conns {
+		h.writeJSON(c, data)
+	}
+}
+
 func applyAccelSamples(clients []ClientView, samples []*pb.AccelSample) []ClientView {
 	if len(samples) == 0 {
 		return clients
@@ -338,7 +362,7 @@ func (h *wsHub) patchClientAccelStream(clientID uint32, enabled bool) {
 		return
 	}
 	for _, c := range conns {
-		_ = c.WriteMessage(websocket.TextMessage, data)
+		h.writeJSON(c, data)
 	}
 }
 
@@ -397,7 +421,7 @@ func (h *wsHub) patchLiveStream(enabled bool) {
 		return
 	}
 	for _, c := range conns {
-		_ = c.WriteMessage(websocket.TextMessage, data)
+		h.writeJSON(c, data)
 	}
 }
 
@@ -430,7 +454,7 @@ func (h *wsHub) patchClientTapNotify(clientID uint32, single, doubleTap, triple
 		return
 	}
 	for _, c := range conns {
-		_ = c.WriteMessage(websocket.TextMessage, data)
+		h.writeJSON(c, data)
 	}
 }
 
@@ -455,7 +479,7 @@ func (h *wsHub) mergeAccel(samples []*pb.AccelSample) {
 		return
 	}
 	for _, c := range conns {
-		_ = c.WriteMessage(websocket.TextMessage, data)
+		h.writeJSON(c, data)
 	}
 }
 
@@ -479,25 +503,16 @@ func (h *wsHub) mergeTap(events []*pb.TapEvent) {
 		return
 	}
 	for _, c := range conns {
-		_ = c.WriteMessage(websocket.TextMessage, data)
+		h.writeJSON(c, data)
 	}
 }
 
 func (h *wsHub) broadcastRaw(v any) {
-	h.mu.RLock()
-	conns := make([]*websocket.Conn, 0, len(h.clients))
-	for c := range h.clients {
-		conns = append(conns, c)
-	}
-	h.mu.RUnlock()
-
 	data, err := json.Marshal(v)
 	if err != nil {
 		return
 	}
-	for _, c := range conns {
-		_ = c.WriteMessage(websocket.TextMessage, data)
-	}
+	h.broadcastJSON(data)
 }
 
 func pollDashboard(link *managedSerial, portName string, last *DashboardState, streamCtl *accelStreamCtl, tapCtl *tapNotifyCtl) DashboardState {
@@ -575,6 +590,9 @@ func pollDashboard(link *managedSerial, portName string, last *DashboardState, s
 
 func applyBatteryToState(link *managedSerial, st *DashboardState) {
 	bat, err := link.BatteryStatusPoll(&pb.BatteryStatusRequest{AllClients: true})
+	if errors.Is(err, errUARTBusy) {
+		return
+	}
 	if err != nil {
 		log.Printf("battery poll: %v", err)
 		return
@@ -602,7 +620,7 @@ func (h *wsHub) mergeBattery(samples []batterySampleJSON) {
 		return
 	}
 	for _, c := range conns {
-		_ = c.WriteMessage(websocket.TextMessage, data)
+		h.writeJSON(c, data)
 	}
 }
 
@@ -619,7 +637,7 @@ func runBatteryPoller(link *managedSerial, hub *wsHub, interval time.Duration, s
 				continue
 			}
 			bat, err := link.BatteryStatusPoll(&pb.BatteryStatusRequest{AllClients: true})
-			if err != nil {
+			if errors.Is(err, errUARTBusy) || err != nil {
 				continue
 			}
 			hub.mergeBattery(batterySamplesFromPB(bat.GetSamples()))