Preserve guest NIC identity before IP assignment (#1319)

internal/monitoring/guest_metadata.go

@@ -592,7 +592,16 @@ func processGuestNetworkInterfaces(raw []proxmox.VMNetworkInterface) ([]string,
 		txBytes := parseInterfaceStat(iface.Statistics, "tx-bytes")
 
 		if len(addresses) == 0 && rxBytes == 0 && txBytes == 0 {
-			continue
+			if len(iface.IPAddresses) > 0 {
+				continue
+			}
+			lowerName := strings.ToLower(ifaceName)
+			if ifaceName == "" || lowerName == "lo" || lowerName == "loopback" {
+				continue
+			}
+			if mac == "" || mac == "00:00:00:00:00:00" {
+				continue
+			}
 		}
 
 		guestIfaces = append(guestIfaces, models.GuestNetworkInterface{

internal/monitoring/guest_metadata_test.go

@@ -508,7 +508,7 @@ func TestProcessGuestNetworkInterfaces(t *testing.T) {
 			},
 		},
 		{
-			name: "interface with no IPs and no traffic is excluded",
+			name: "interface with no IPs and no traffic keeps non-loopback identity",
 			raw: []proxmox.VMNetworkInterface{
 				{
 					Name:         "eth0",
@@ -517,6 +517,21 @@ func TestProcessGuestNetworkInterfaces(t *testing.T) {
 					Statistics:   nil,
 				},
 			},
+			wantIPs: []string{},
+			wantIfaces: []models.GuestNetworkInterface{
+				{Name: "eth0", MAC: "00:11:22:33:44:55", Addresses: nil},
+			},
+		},
+		{
+			name: "loopback-only interface with no IPs and no traffic is excluded",
+			raw: []proxmox.VMNetworkInterface{
+				{
+					Name:         "lo",
+					HardwareAddr: "00:00:00:00:00:00",
+					IPAddresses:  nil,
+					Statistics:   nil,
+				},
+			},
 			wantIPs:    []string{},
 			wantIfaces: []models.GuestNetworkInterface{},
 		},