feat: add JoeAppEngine OPC UA nodes, fix DCL auto-reconnect and quality push

- Add JoeAppEngine folder to OPC UA nodes.json (BTCS, AlarmCntsBySeverity, Scheduler/ScanTime)
- Fix DataConnectionActor: capture Self in PreStart for use from non-actor threads,
  preventing Self.Tell failure in Disconnected event handler
- Implement InstanceActor.HandleConnectionQualityChanged to mark attributes Bad on disconnect
- Fix LmxFakeProxy TagMapper to serialize arrays as JSON instead of "System.Int32[]"
- Allow DataType and DataSourceReference updates in TemplateService.UpdateAttributeAsync
- Update test_infra_opcua.md with JoeAppEngine documentation

src/ScadaLink.DataConnectionLayer/Adapters/RealOpcUaClient.cs

@@ -14,31 +14,44 @@ public class RealOpcUaClient : IOpcUaClient
     private Subscription? _subscription;
     private readonly Dictionary<string, MonitoredItem> _monitoredItems = new();
     private readonly Dictionary<string, Action<string, object?, DateTime, uint>> _callbacks = new();
+    private volatile bool _connectionLostFired;
+    private OpcUaConnectionOptions _options = new();
 
     public bool IsConnected => _session?.Connected ?? false;
+    public event Action? ConnectionLost;
 
-    public async Task ConnectAsync(string endpointUrl, CancellationToken cancellationToken = default)
+    public async Task ConnectAsync(string endpointUrl, OpcUaConnectionOptions? options = null, CancellationToken cancellationToken = default)
     {
+        var opts = options ?? new OpcUaConnectionOptions();
+
+        var preferredSecurityMode = opts.SecurityMode?.ToUpperInvariant() switch
+        {
+            "SIGN" => MessageSecurityMode.Sign,
+            "SIGNANDENCRYPT" => MessageSecurityMode.SignAndEncrypt,
+            _ => MessageSecurityMode.None
+        };
+
         var appConfig = new ApplicationConfiguration
         {
             ApplicationName = "ScadaLink-DCL",
             ApplicationType = ApplicationType.Client,
             SecurityConfiguration = new SecurityConfiguration
             {
-                AutoAcceptUntrustedCertificates = true,
+                AutoAcceptUntrustedCertificates = opts.AutoAcceptUntrustedCerts,
                 ApplicationCertificate = new CertificateIdentifier(),
                 TrustedIssuerCertificates = new CertificateTrustList { StorePath = Path.Combine(Path.GetTempPath(), "ScadaLink", "pki", "issuers") },
                 TrustedPeerCertificates = new CertificateTrustList { StorePath = Path.Combine(Path.GetTempPath(), "ScadaLink", "pki", "trusted") },
                 RejectedCertificateStore = new CertificateTrustList { StorePath = Path.Combine(Path.GetTempPath(), "ScadaLink", "pki", "rejected") }
             },
-            ClientConfiguration = new ClientConfiguration { DefaultSessionTimeout = 60000 },
-            TransportQuotas = new TransportQuotas { OperationTimeout = 15000 }
+            ClientConfiguration = new ClientConfiguration { DefaultSessionTimeout = opts.SessionTimeoutMs },
+            TransportQuotas = new TransportQuotas { OperationTimeout = opts.OperationTimeoutMs }
         };
 
         await appConfig.ValidateAsync(ApplicationType.Client);
-        appConfig.CertificateValidator.CertificateValidation += (_, e) => e.Accept = true;
+        if (opts.AutoAcceptUntrustedCerts)
+            appConfig.CertificateValidator.CertificateValidation += (_, e) => e.Accept = true;
 
-        // Discover endpoints from the server, pick the no-security one
+        // Discover endpoints from the server, pick the preferred security mode
         EndpointDescription? endpoint;
         try
         {
@@ -49,7 +62,7 @@ public class RealOpcUaClient : IOpcUaClient
             var endpoints = discoveryClient.GetEndpoints(null);
 #pragma warning restore CS0618
             endpoint = endpoints
-                .Where(e => e.SecurityMode == MessageSecurityMode.None)
+                .Where(e => e.SecurityMode == preferredSecurityMode)
                 .FirstOrDefault() ?? endpoints.FirstOrDefault();
         }
         catch
@@ -66,17 +79,24 @@ public class RealOpcUaClient : IOpcUaClient
 #pragma warning restore CS0618
         _session = await sessionFactory.CreateAsync(
             appConfig, configuredEndpoint, false,
-            "ScadaLink-DCL-Session", 60000, null, null, cancellationToken);
+            "ScadaLink-DCL-Session", (uint)opts.SessionTimeoutMs, null, null, cancellationToken);
+
+        // Detect server going offline via keep-alive failures
+        _connectionLostFired = false;
+        _session.KeepAlive += OnSessionKeepAlive;
+
+        // Store options for monitored item creation
+        _options = opts;
 
         // Create a default subscription for all monitored items
         _subscription = new Subscription(_session.DefaultSubscription)
         {
             DisplayName = "ScadaLink",
             PublishingEnabled = true,
-            PublishingInterval = 1000,
-            KeepAliveCount = 10,
-            LifetimeCount = 30,
-            MaxNotificationsPerPublish = 100
+            PublishingInterval = opts.PublishingIntervalMs,
+            KeepAliveCount = (uint)opts.KeepAliveCount,
+            LifetimeCount = (uint)opts.LifetimeCount,
+            MaxNotificationsPerPublish = (uint)opts.MaxNotificationsPerPublish
         };
 
         _session.AddSubscription(_subscription);
@@ -92,6 +112,7 @@ public class RealOpcUaClient : IOpcUaClient
         }
         if (_session != null)
         {
+            _session.KeepAlive -= OnSessionKeepAlive;
             await _session.CloseAsync(cancellationToken);
             _session = null;
         }
@@ -112,8 +133,8 @@ public class RealOpcUaClient : IOpcUaClient
             DisplayName = nodeId,
             StartNodeId = nodeId,
             AttributeId = Attributes.Value,
-            SamplingInterval = 1000,
-            QueueSize = 10,
+            SamplingInterval = _options.SamplingIntervalMs,
+            QueueSize = (uint)_options.QueueSize,
             DiscardOldest = true
         };
 
@@ -188,6 +209,20 @@ public class RealOpcUaClient : IOpcUaClient
         return response.Results[0].Code;
     }
 
+    /// <summary>
+    /// Called by the OPC UA SDK when a keep-alive response arrives (or fails).
+    /// When CurrentState is bad, the server is unreachable.
+    /// </summary>
+    private void OnSessionKeepAlive(ISession session, KeepAliveEventArgs e)
+    {
+        if (ServiceResult.IsBad(e.Status))
+        {
+            if (_connectionLostFired) return;
+            _connectionLostFired = true;
+            ConnectionLost?.Invoke();
+        }
+    }
+
     public async ValueTask DisposeAsync()
     {
         await DisconnectAsync();