Refactor RDP proxy handling and update related tests

agents/rap-node-agent/internal/vpnruntime/gateway.go

@@ -169,6 +169,9 @@ func (g *Gateway) Snapshot() map[string]any {
 
 	out := map[string]any{
 		"running":                   running,
+		"service_role":              "ipv4-egress",
+		"service_class":             "vpn_packets",
+		"adapter_contract":          "fabric_channel_to_ipv4_nat",
 		"transport":                 g.transportName(),
 		"poll_timeout_ms":           g.PollTimeout.Milliseconds(),
 		"client_to_gateway_batches": g.clientToGatewayBatches.Load(),
@@ -234,14 +237,7 @@ func (g *Gateway) setStopped(err error) {
 
 func (g *Gateway) normalize() error {
 	if g.Transport == nil {
-		if g.API == nil {
-			return fmt.Errorf("api client or packet transport is required")
-		}
-		g.Transport = BackendPacketTransport{
-			API:             g.API,
-			ClusterID:       g.ClusterID,
-			VPNConnectionID: g.VPNConnectionID,
-		}
+		return fmt.Errorf("fabric packet transport is required; backend packet relay fallback is disabled")
 	}
 	if g.ClusterID == "" || g.VPNConnectionID == "" {
 		return fmt.Errorf("cluster id and vpn connection id are required")