feat(dcl): extend CreateConnectionCommand with backup config and failover retry count

Update CreateConnectionCommand to carry PrimaryConnectionDetails,
BackupConnectionDetails, and FailoverRetryCount. Update all callers:
DataConnectionManagerActor, DataConnectionActor, DeploymentManagerActor,
FlatteningService, and ConnectionConfig. The actor stores both configs
but continues using primary only — failover logic comes in Task 3.

src/ScadaLink.Commons/Messages/DataConnection/CreateConnectionCommand.cs

@@ -7,4 +7,6 @@ namespace ScadaLink.Commons.Messages.DataConnection;
 public record CreateConnectionCommand(
     string ConnectionName,
     string ProtocolType,
-    IDictionary<string, string> ConnectionDetails);
+    IDictionary<string, string> PrimaryConnectionDetails,
+    IDictionary<string, string>? BackupConnectionDetails = null,
+    int FailoverRetryCount = 3);

src/ScadaLink.Commons/Types/Flattening/FlattenedConfiguration.cs

@@ -33,6 +33,8 @@ public sealed record ConnectionConfig
 {
     public string Protocol { get; init; } = string.Empty;
     public string? ConfigurationJson { get; init; }
+    public string? BackupConfigurationJson { get; init; }
+    public int FailoverRetryCount { get; init; } = 3;
 }
 
 /// <summary>

src/ScadaLink.DataConnectionLayer/Actors/DataConnectionActor.cs

@@ -61,6 +61,9 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
     private int _resolvedTags;
 
     private readonly IDictionary<string, string> _connectionDetails;
+    private readonly IDictionary<string, string> _primaryConfig;
+    private readonly IDictionary<string, string>? _backupConfig;
+    private readonly int _failoverRetryCount;
 
     /// <summary>
     /// Captured Self reference for use from non-actor threads (event handlers, callbacks).
@@ -73,13 +76,18 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
         IDataConnection adapter,
         DataConnectionOptions options,
         ISiteHealthCollector healthCollector,
-        IDictionary<string, string>? connectionDetails = null)
+        IDictionary<string, string>? primaryConfig = null,
+        IDictionary<string, string>? backupConfig = null,
+        int failoverRetryCount = 3)
     {
         _connectionName = connectionName;
         _adapter = adapter;
         _options = options;
         _healthCollector = healthCollector;
-        _connectionDetails = connectionDetails ?? new Dictionary<string, string>();
+        _primaryConfig = primaryConfig ?? new Dictionary<string, string>();
+        _backupConfig = backupConfig;
+        _failoverRetryCount = failoverRetryCount;
+        _connectionDetails = _primaryConfig;
     }
 
     protected override void PreStart()

src/ScadaLink.DataConnectionLayer/Actors/DataConnectionManagerActor.cs

@@ -45,10 +45,13 @@ public class DataConnectionManagerActor : ReceiveActor
         }
 
         // WP-34: Factory creates the correct adapter based on protocol type
-        var adapter = _factory.Create(command.ProtocolType, command.ConnectionDetails);
+        var adapter = _factory.Create(command.ProtocolType, command.PrimaryConnectionDetails);
 
         var props = Props.Create(() => new DataConnectionActor(
-            command.ConnectionName, adapter, _options, _healthCollector, command.ConnectionDetails));
+            command.ConnectionName, adapter, _options, _healthCollector,
+            command.PrimaryConnectionDetails,
+            command.BackupConnectionDetails,
+            command.FailoverRetryCount));
 
         // Sanitize name for Akka actor path (replace spaces and invalid chars)
         var actorName = new string(command.ConnectionName

src/ScadaLink.SiteRuntime/Actors/DeploymentManagerActor.cs

@@ -422,7 +422,7 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
                 if (_createdConnections.Contains(name))
                     continue;
 
-                var connectionDetails = new Dictionary<string, string>();
+                var primaryDetails = new Dictionary<string, string>();
                 if (!string.IsNullOrEmpty(connConfig.ConfigurationJson))
                 {
                     try
@@ -431,14 +431,29 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
                         using var doc = System.Text.Json.JsonDocument.Parse(connConfig.ConfigurationJson);
                         foreach (var prop in doc.RootElement.EnumerateObject())
                         {
-                            connectionDetails[prop.Name] = prop.Value.ToString();
+                            primaryDetails[prop.Name] = prop.Value.ToString();
                         }
                     }
                     catch { /* Ignore parse errors */ }
                 }
 
+                Dictionary<string, string>? backupDetails = null;
+                if (!string.IsNullOrEmpty(connConfig.BackupConfigurationJson))
+                {
+                    try
+                    {
+                        backupDetails = new Dictionary<string, string>();
+                        using var doc = System.Text.Json.JsonDocument.Parse(connConfig.BackupConfigurationJson);
+                        foreach (var prop in doc.RootElement.EnumerateObject())
+                        {
+                            backupDetails[prop.Name] = prop.Value.ToString();
+                        }
+                    }
+                    catch { backupDetails = null; /* Ignore parse errors */ }
+                }
+
                 _dclManager.Tell(new Commons.Messages.DataConnection.CreateConnectionCommand(
-                    name, connConfig.Protocol, connectionDetails));
+                    name, connConfig.Protocol, primaryDetails, backupDetails, connConfig.FailoverRetryCount));
 
                 _createdConnections.Add(name);
                 _logger.LogInformation(

src/ScadaLink.TemplateEngine/Flattening/FlatteningService.cs

@@ -90,7 +90,9 @@ public class FlatteningService
                         connections[attr.BoundDataConnectionName] = new ConnectionConfig
                         {
                             Protocol = conn.Protocol,
-                            ConfigurationJson = conn.PrimaryConfiguration
+                            ConfigurationJson = conn.PrimaryConfiguration,
+                            BackupConfigurationJson = conn.BackupConfiguration,
+                            FailoverRetryCount = conn.FailoverRetryCount
                         };
                     }
                 }

tests/ScadaLink.DataConnectionLayer.Tests/DataConnectionManagerActorTests.cs

@@ -70,7 +70,7 @@ public class DataConnectionManagerActorTests : TestKit
             new DataConnectionManagerActor(_mockFactory, _options, _mockHealthCollector)));
 
         manager.Tell(new CreateConnectionCommand(
-            "conn1", "OpcUa", new Dictionary<string, string>()));
+            "conn1", "OpcUa", new Dictionary<string, string>(), null, 3));
 
         // Factory should have been called
         AwaitCondition(() =>