gs: Fix rctx field name in LBS LNS upstream messages

The rctx field in the upinfo object of upstream messages was misspelled
as rtcx, so the radio context reported by gateways was ignored and the
antenna index in the uplink metadata was always 0. The parsed value is
now reflected in the uplink metadata and echoed in class A downlinks.

Author: vlasebian

CHANGELOG.md

@@ -21,6 +21,8 @@ For details about compatibility between different releases, see the **Commitment
 
 ### Fixed
 
+- Parsing of the `rctx` field in the `upinfo` object of upstream messages received via the LoRa Basics Station LNS protocol. The field name was misspelled as `rtcx`, so the radio context reported by gateways was ignored. The antenna index in the uplink metadata now reflects the reported radio context and is echoed back in class A downlinks, instead of always being 0.
+
 ### Security
 
 ## [3.36.2] - 2026-08-17

pkg/gatewayserver/io/semtechws/lbslns/upstream.go

@@ -44,7 +44,7 @@ var (
 // UpInfo provides additional metadata on each upstream message.
 type UpInfo struct {
 	RxTime  float64 `json:"rxtime"`
-	RCtx    int64   `json:"rtcx"`
+	RCtx    int64   `json:"rctx"`
 	XTime   int64   `json:"xtime"`
 	GPSTime int64   `json:"gpstime"`
 	RSSI    float32 `json:"rssi"`

pkg/gatewayserver/io/semtechws/lbslns/upstream_test.go

@@ -61,7 +61,7 @@ func TestMarshalJSON(t *testing.T) {
 					},
 				},
 			},
-			Expected: []byte(`{"msgtype":"jreq","MHdr":0,"JoinEui":"2222:2222:2222:2222","DevEui":"1111:1111:1111:1111","DevNonce":18000,"MIC":12345678,"RefTime":0,"DR":1,"Freq":868300000,"upinfo":{"rxtime":1548059982,"rtcx":0,"xtime":12666373963464220,"gpstime":0,"rssi":89,"snr":9.25}}`), //nolint: lll
+			Expected: []byte(`{"msgtype":"jreq","MHdr":0,"JoinEui":"2222:2222:2222:2222","DevEui":"1111:1111:1111:1111","DevNonce":18000,"MIC":12345678,"RefTime":0,"DR":1,"Freq":868300000,"upinfo":{"rxtime":1548059982,"rctx":0,"xtime":12666373963464220,"gpstime":0,"rssi":89,"snr":9.25}}`), //nolint: lll
 		},
 		{
 			Name: "UplinkDataFrame",
@@ -85,7 +85,7 @@ func TestMarshalJSON(t *testing.T) {
 					},
 				},
 			},
-			Expected: []byte(`{"msgtype":"updf","MHdr":64,"DevAddr":287454020,"FCtrl":48,"Fcnt":25,"FOpts":"FD","FPort":0,"FRMPayload":"Ymxhamthc25kJ3M=","MIC":12345678,"RefTime":0,"DR":1,"Freq":868300000,"upinfo":{"rxtime":1548059982,"rtcx":0,"xtime":12666373963464220,"gpstime":0,"rssi":89,"snr":9.25}}`), //nolint: lll
+			Expected: []byte(`{"msgtype":"updf","MHdr":64,"DevAddr":287454020,"FCtrl":48,"Fcnt":25,"FOpts":"FD","FPort":0,"FRMPayload":"Ymxhamthc25kJ3M=","MIC":12345678,"RefTime":0,"DR":1,"Freq":868300000,"upinfo":{"rxtime":1548059982,"rctx":0,"xtime":12666373963464220,"gpstime":0,"rssi":89,"snr":9.25}}`), //nolint: lll
 		},
 		{
 			Name: "TxConfirmation",