feat(dcl): add active endpoint to health reports and log failover events

Add ActiveEndpoint field to DataConnectionHealthReport showing which
endpoint is active (Primary, Backup, or Primary with no backup configured).
Log failover transitions and connection restoration events to the site
event log via ISiteEventLogger, passed as an optional parameter through
the actor hierarchy for backwards compatibility.

src/ScadaLink.DataConnectionLayer/Actors/DataConnectionActor.cs

@@ -4,6 +4,7 @@ using ScadaLink.Commons.Interfaces.Protocol;
 using ScadaLink.Commons.Messages.DataConnection;
 using ScadaLink.Commons.Types.Enums;
 using ScadaLink.HealthMonitoring;
+using ScadaLink.SiteEventLogging;
 
 namespace ScadaLink.DataConnectionLayer.Actors;
 
@@ -34,6 +35,7 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
     private readonly ISiteHealthCollector _healthCollector;
     private readonly IDataConnectionFactory _factory;
     private readonly string _protocolType;
+    private readonly ISiteEventLogger? _siteEventLogger;
 
     public IStash Stash { get; set; } = null!;
     public ITimerScheduler Timers { get; set; } = null!;
@@ -86,7 +88,8 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
         string protocolType,
         IDictionary<string, string>? primaryConfig = null,
         IDictionary<string, string>? backupConfig = null,
-        int failoverRetryCount = 3)
+        int failoverRetryCount = 3,
+        ISiteEventLogger? siteEventLogger = null)
     {
         _connectionName = connectionName;
         _adapter = adapter;
@@ -97,6 +100,7 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
         _primaryConfig = primaryConfig ?? new Dictionary<string, string>();
         _backupConfig = backupConfig;
         _failoverRetryCount = failoverRetryCount;
+        _siteEventLogger = siteEventLogger;
         _connectionDetails = _primaryConfig;
     }
 
@@ -301,6 +305,14 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
             _log.Info("[{0}] Reconnected successfully on {1} endpoint", _connectionName, _activeEndpoint);
             _consecutiveFailures = 0;
 
+            // Log restoration event to site event log
+            if (_siteEventLogger != null)
+            {
+                _ = _siteEventLogger.LogEventAsync(
+                    "connection", "Info", null, _connectionName,
+                    $"Connection restored on {_activeEndpoint} endpoint", null);
+            }
+
             // WP-10: Transparent re-subscribe — re-establish all active subscriptions
             ReSubscribeAll();
 
@@ -336,6 +348,15 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
 
                 _log.Warning("[{0}] Failing over from {1} to {2}",
                     _connectionName, previousEndpoint, _activeEndpoint);
+
+                // Log failover event to site event log
+                if (_siteEventLogger != null)
+                {
+                    _ = _siteEventLogger.LogEventAsync(
+                        "connection", "Warning", null, _connectionName,
+                        $"Failover from {previousEndpoint} to {_activeEndpoint}",
+                        $"After {_failoverRetryCount} consecutive failures");
+                }
             }
             else
             {
@@ -570,8 +591,11 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
     private void ReplyWithHealthReport()
     {
         var status = _adapter.Status;
+        var endpointLabel = _backupConfig == null
+            ? "Primary (no backup)"
+            : _activeEndpoint.ToString();
         Sender.Tell(new DataConnectionHealthReport(
-            _connectionName, status, _totalSubscribed, _resolvedTags, DateTimeOffset.UtcNow));
+            _connectionName, status, _totalSubscribed, _resolvedTags, endpointLabel, DateTimeOffset.UtcNow));
     }
 
     // ── Internal message handlers for piped async results ──