Add CACHE_STATUS UART poll and dashboard live stream.

Combine cached accel and tap in one low-overhead master command for ~16 ms
host polling. The dashboard uses a single live-stream toggle plus per-slave
accel-stream controls; fix live_stream state so polling is not cleared every
slow client refresh.

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

goTool/client_api.go

@@ -192,6 +192,36 @@ func (m *managedSerial) tapNotifyVia(
 	return resp, err
 }
 
+func (m *managedSerial) readCacheStatusPoll() (*pb.CacheStatusResponse, error) {
+	payload, err := m.exchangePoll(byte(pb.MessageType_CACHE_STATUS), "CACHE_STATUS")
+	if err != nil {
+		return nil, err
+	}
+	return decodeCacheStatusPayload(payload)
+}
+
+func decodeCacheStatusPayload(payload []byte) (*pb.CacheStatusResponse, error) {
+	if len(payload) < 1 {
+		return nil, fmt.Errorf("empty response payload")
+	}
+	if payload[0] != byte(pb.MessageType_CACHE_STATUS) {
+		return nil, fmt.Errorf("unexpected command id 0x%02x (want 0x%02x)",
+			payload[0], byte(pb.MessageType_CACHE_STATUS))
+	}
+	var msg pb.UartMessage
+	if err := proto.Unmarshal(payload[1:], &msg); err != nil {
+		return nil, fmt.Errorf("decode: %w", err)
+	}
+	if msg.GetType() != pb.MessageType_CACHE_STATUS {
+		return nil, fmt.Errorf("unexpected type %v", msg.GetType())
+	}
+	r := msg.GetCacheStatusResponse()
+	if r == nil {
+		return nil, fmt.Errorf("missing cache_status_response")
+	}
+	return r, nil
+}
+
 func (m *managedSerial) readTapSnapshotPoll(clientID uint32) (*pb.TapSnapshotResponse, error) {
 	msg := &pb.UartMessage{
 		Type: pb.MessageType_TAP_SNAPSHOT,
@@ -410,6 +440,14 @@ func (s *serialPort) TapNotify(req *pb.TapNotifyRequest) (*pb.TapNotifyResponse,
 	return r, nil
 }
 
+func (s *serialPort) readCacheStatus() (*pb.CacheStatusResponse, error) {
+	payload, err := s.exchange(byte(pb.MessageType_CACHE_STATUS), "CACHE_STATUS")
+	if err != nil {
+		return nil, err
+	}
+	return decodeCacheStatusPayload(payload)
+}
+
 func (s *serialPort) readTapSnapshot(clientID uint32) (*pb.TapSnapshotResponse, error) {
 	msg := &pb.UartMessage{
 		Type: pb.MessageType_TAP_SNAPSHOT,