Explicitly reject detour to empty direct outbounds

dns/transport/udp.go

@@ -7,6 +7,7 @@ import (
 	"sync"
 
 	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing-box/common/dialer"
 	C "github.com/sagernet/sing-box/constant"
 	"github.com/sagernet/sing-box/dns"
 	"github.com/sagernet/sing-box/log"
@@ -64,11 +65,19 @@ func NewUDPRaw(logger logger.ContextLogger, adapter dns.TransportAdapter, dialer
 	}
 }
 
-func (t *UDPTransport) Reset() {
+func (t *UDPTransport) Start(stage adapter.StartStage) error {
+	if stage != adapter.StartStateStart {
+		return nil
+	}
+	return dialer.InitializeDetour(t.dialer)
+}
+
+func (t *UDPTransport) Close() error {
 	t.access.Lock()
 	defer t.access.Unlock()
 	close(t.done)
 	t.done = make(chan struct{})
+	return nil
 }
 
 func (t *UDPTransport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {