fix: Enrollment-Duplikate, IPv6-Adresse, Agent-Status

- Backend: Enroll-Upsert via MAC-Adresse (kein Duplikat bei Neustart)
  HeartbeatInterval auf 30s reduziert
- Go collector: IPv4 bevorzugen, Loopback/Teredo/ISATAP überspringen,
  Link-Local IPv6 ignorieren
- Go main.go: Enrollment nimmt beste IPv4-Schnittstelle statt Networks[0]

Agent/cmd/agent/main.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"os/signal"
 	"runtime"
+	"strings"
 	"syscall"
 	"time"
 
@@ -40,10 +41,20 @@ func main() {
 	if cfg.AgentID == "" {
 		hostname, _ := os.Hostname()
 		metrics, _ := collector.Collect()
+		// Beste Netzwerkschnittstelle für Enrollment wählen (bevorzuge IPv4)
 		mac, ip := "", ""
-		if len(metrics.Networks) > 0 {
+		for _, n := range metrics.Networks {
-			mac = metrics.Networks[0].MAC
+			if n.MAC == "" || n.IPAddress == "" {
-			ip = metrics.Networks[0].IPAddress
+				continue
+			}
+			if mac == "" {
+				mac, ip = n.MAC, n.IPAddress
+			}
+			// Sobald IPv4 gefunden: nehmen und fertig
+			if !strings.Contains(n.IPAddress, ":") {
+				mac, ip = n.MAC, n.IPAddress
+				break
+			}
 		}
 
 		resp, err := client.Client.Enroll(context.Background(), &pb.EnrollRequest{

Agent/internal/collector/collector.go

@@ -1,6 +1,8 @@
 package collector
 
 import (
+	"net"
+	"strings"
 	"time"
 
 	"github.com/shirou/gopsutil/v3/cpu"
@@ -79,15 +81,41 @@ func Collect() (*Metrics, error) {
 		counterMap[c.Name] = c
 	}
 	for _, iface := range interfaces {
-		if len(iface.Addrs) == 0 {
+		if len(iface.Addrs) == 0 || iface.HardwareAddr == "" {
+			continue
+		}
+		// Loopback und virtuelle Adapter überspringen
+		nameLower := strings.ToLower(iface.Name)
+		if strings.Contains(nameLower, "loopback") || strings.Contains(nameLower, "teredo") ||
+			strings.Contains(nameLower, "isatap") || strings.Contains(nameLower, "6to4") {
 			continue
 		}
 		ni := NetInfo{
 			Name: iface.Name,
 			MAC:  iface.HardwareAddr,
 		}
-		if len(iface.Addrs) > 0 {
+		// IPv4 bevorzugen, IPv6 als Fallback
-			ni.IPAddress = iface.Addrs[0].Addr
+		for _, addr := range iface.Addrs {
+			ip, _, err := net.ParseCIDR(addr.Addr)
+			if err != nil {
+				// Versuche direkte IP-Adresse (ohne CIDR)
+				ip = net.ParseIP(addr.Addr)
+			}
+			if ip == nil || ip.IsLoopback() || ip.IsLinkLocalUnicast() {
+				continue
+			}
+			if ip.To4() != nil {
+				// IPv4 gefunden — nehmen und abbrechen
+				ni.IPAddress = addr.Addr
+				break
+			}
+			if ni.IPAddress == "" {
+				// IPv6 als vorläufiger Fallback
+				ni.IPAddress = addr.Addr
+			}
+		}
+		if ni.IPAddress == "" {
+			continue
 		}
 		if c, ok := counterMap[iface.Name]; ok {
 			ni.BytesSent = c.BytesSent

Backend/src/NexusRMM.Api/GrpcServices/AgentGrpcService.cs

@@ -29,6 +29,24 @@ public class AgentGrpcService : AgentService.AgentServiceBase
 
     public override async Task<EnrollResponse> Enroll(EnrollRequest request, ServerCallContext context)
     {
+        // Upsert via MAC-Adresse — verhindert Duplikate bei Agent-Neustart
+        var existing = !string.IsNullOrEmpty(request.MacAddress)
+            ? await _db.Agents.FirstOrDefaultAsync(a => a.MacAddress == request.MacAddress)
+            : null;
+
+        if (existing is not null)
+        {
+            existing.Hostname = request.Hostname;
+            existing.OsVersion = request.OsVersion;
+            existing.IpAddress = request.IpAddress;
+            existing.AgentVersion = request.AgentVersion;
+            existing.Status = AgentStatus.Online;
+            existing.LastSeen = DateTime.UtcNow;
+            await _db.SaveChangesAsync();
+            _logger.LogInformation("Agent re-enrolled: {AgentId} ({Hostname})", existing.Id, existing.Hostname);
+            return new EnrollResponse { AgentId = existing.Id.ToString(), HeartbeatInterval = 30 };
+        }
+
         var agent = new AgentModel
         {
             Id = Guid.NewGuid(),
@@ -47,11 +65,7 @@ public class AgentGrpcService : AgentService.AgentServiceBase
         await _db.SaveChangesAsync();
         _logger.LogInformation("Agent enrolled: {AgentId} ({Hostname})", agent.Id, agent.Hostname);
 
-        return new EnrollResponse
+        return new EnrollResponse { AgentId = agent.Id.ToString(), HeartbeatInterval = 30 };
-        {
-            AgentId = agent.Id.ToString(),
-            HeartbeatInterval = 60
-        };
     }
 
     public override async Task<HeartbeatResponse> Heartbeat(HeartbeatRequest request, ServerCallContext context)