fix: route debug stream events through ClusterClient site→central path

ClusterClient Sender refs are temporary proxies — valid for immediate reply
but not durable for future Tells. Events now flow as DebugStreamEvent through
SiteCommunicationActor → ClusterClient → CentralCommunicationActor → bridge
actor (same pattern as health reports). Also fix DebugStreamHub to use
IHubContext for long-lived callbacks instead of transient hub instance.

src/ScadaLink.Commons/Messages/DebugView/DebugStreamEvent.cs

@@ -0,0 +1,8 @@
+namespace ScadaLink.Commons.Messages.DebugView;
+
+/// <summary>
+/// Wraps a debug stream event (AttributeValueChanged or AlarmStateChanged) with
+/// the correlationId for routing back to the correct DebugStreamBridgeActor on central.
+/// Sent from InstanceActor → SiteCommunicationActor → ClusterClient → CentralCommunicationActor.
+/// </summary>
+public record DebugStreamEvent(string CorrelationId, object Event);

src/ScadaLink.Communication/Actors/CentralCommunicationActor.cs

@@ -85,6 +85,9 @@ public class CentralCommunicationActor : ReceiveActor
 
         // Route enveloped messages to sites
         Receive<SiteEnvelope>(HandleSiteEnvelope);
+
+        // Route debug stream events from sites to the correct bridge actor
+        Receive<Commons.Messages.DebugView.DebugStreamEvent>(HandleDebugStreamEvent);
     }
 
     private void HandleHeartbeat(HeartbeatMessage heartbeat)
@@ -93,6 +96,18 @@ public class CentralCommunicationActor : ReceiveActor
         Context.Parent.Tell(heartbeat);
     }
 
+    private void HandleDebugStreamEvent(Commons.Messages.DebugView.DebugStreamEvent msg)
+    {
+        if (_debugSubscriptions.TryGetValue(msg.CorrelationId, out var entry))
+        {
+            entry.Subscriber.Tell(msg.Event);
+        }
+        else
+        {
+            _log.Debug("No debug subscription found for correlationId {0}, dropping event", msg.CorrelationId);
+        }
+    }
+
     private void HandleSiteHealthReport(SiteHealthReport report)
     {
         var aggregator = _serviceProvider.GetService<ICentralHealthAggregator>();

src/ScadaLink.Communication/Actors/SiteCommunicationActor.cs

@@ -145,6 +145,13 @@ public class SiteCommunicationActor : ReceiveActor, IWithTimers
             _centralClient?.Tell(
                 new ClusterClient.Send("/user/central-communication", msg), Self);
         });
+
+        // Internal: forward debug stream events to central (site→central streaming)
+        Receive<DebugStreamEvent>(msg =>
+        {
+            _centralClient?.Tell(
+                new ClusterClient.Send("/user/central-communication", msg), Self);
+        });
     }
 
     protected override void PreStart()

src/ScadaLink.ManagementService/DebugStreamHub.cs

@@ -19,11 +19,16 @@ public class DebugStreamHub : Hub
     private const string SessionIdKey = "DebugStreamSessionId";
 
     private readonly DebugStreamService _debugStreamService;
+    private readonly IHubContext<DebugStreamHub> _hubContext;
     private readonly ILogger<DebugStreamHub> _logger;
 
-    public DebugStreamHub(DebugStreamService debugStreamService, ILogger<DebugStreamHub> logger)
+    public DebugStreamHub(
+        DebugStreamService debugStreamService,
+        IHubContext<DebugStreamHub> hubContext,
+        ILogger<DebugStreamHub> logger)
     {
         _debugStreamService = debugStreamService;
+        _hubContext = hubContext;
         _logger = logger;
     }
 
@@ -105,6 +110,10 @@ public class DebugStreamHub : Hub
 
         try
         {
+            // Use IHubContext for callbacks — the hub instance is transient (disposed after method returns),
+            // but IHubContext is a singleton that remains valid for the lifetime of the connection.
+            var hubClients = _hubContext.Clients;
+
             var session = await _debugStreamService.StartStreamAsync(
                 instanceId,
                 onEvent: evt =>
@@ -113,17 +122,17 @@ public class DebugStreamHub : Hub
                     _ = evt switch
                     {
                         AttributeValueChanged changed =>
-                            Clients.Client(connectionId).SendAsync("OnAttributeChanged", changed),
+                            hubClients.Client(connectionId).SendAsync("OnAttributeChanged", changed),
                         AlarmStateChanged changed =>
-                            Clients.Client(connectionId).SendAsync("OnAlarmChanged", changed),
+                            hubClients.Client(connectionId).SendAsync("OnAlarmChanged", changed),
                         DebugViewSnapshot snapshot =>
-                            Clients.Client(connectionId).SendAsync("OnSnapshot", snapshot),
+                            hubClients.Client(connectionId).SendAsync("OnSnapshot", snapshot),
                         _ => Task.CompletedTask
                     };
                 },
                 onTerminated: () =>
                 {
-                    _ = Clients.Client(connectionId).SendAsync("OnStreamTerminated", "Site disconnected");
+                    _ = hubClients.Client(connectionId).SendAsync("OnStreamTerminated", "Site disconnected");
                 });
 
             Context.Items[SessionIdKey] = session.SessionId;

src/ScadaLink.SiteRuntime/Actors/InstanceActor.cs

@@ -51,7 +51,8 @@ public class InstanceActor : ReceiveActor
     private FlattenedConfiguration? _configuration;
 
     // WP-25: Debug view subscribers
-    private readonly Dictionary<string, IActorRef> _debugSubscribers = new();
+    private readonly HashSet<string> _debugSubscriberCorrelationIds = new();
+    private ActorSelection? _siteCommActor;
 
     // DCL manager actor reference for subscribing to tag values
     private readonly IActorRef? _dclManager;
@@ -149,6 +150,9 @@ public class InstanceActor : ReceiveActor
         base.PreStart();
         _logger.LogInformation("InstanceActor started for {Instance}", _instanceUniqueName);
 
+        // Resolve SiteCommunicationActor for routing debug stream events back to central
+        _siteCommActor = Context.ActorSelection("/user/site-communication");
+
         // Asynchronously load static overrides from SQLite and pipe to self
         var self = Self;
         _storage.GetStaticOverridesAsync(_instanceUniqueName).ContinueWith(t =>
@@ -367,10 +371,10 @@ public class InstanceActor : ReceiveActor
         // WP-23: Publish to site-wide stream
         _streamManager?.PublishAlarmStateChanged(changed);
 
-        // Forward to debug subscribers
-        foreach (var sub in _debugSubscribers.Values)
+        // Forward to debug subscribers via SiteCommunicationActor → ClusterClient → central
+        foreach (var correlationId in _debugSubscriberCorrelationIds)
         {
-            sub.Tell(changed);
+            _siteCommActor?.Tell(new DebugStreamEvent(correlationId, changed));
         }
     }
 
@@ -380,7 +384,7 @@ public class InstanceActor : ReceiveActor
     private void HandleSubscribeDebugView(SubscribeDebugViewRequest request)
     {
         var subscriptionId = request.CorrelationId;
-        _debugSubscribers[subscriptionId] = Sender;
+        _debugSubscriberCorrelationIds.Add(subscriptionId);
 
         // Build snapshot from current state
         var now = DateTimeOffset.UtcNow;
@@ -407,9 +411,6 @@ public class InstanceActor : ReceiveActor
 
         Sender.Tell(snapshot);
 
-        // Also register with stream manager for filtered events
-        _streamManager?.Subscribe(_instanceUniqueName, Sender);
-
         _logger.LogDebug(
             "Debug view subscriber added for {Instance}, subscriptionId={Id}",
             _instanceUniqueName, subscriptionId);
@@ -420,8 +421,7 @@ public class InstanceActor : ReceiveActor
     /// </summary>
     private void HandleUnsubscribeDebugView(UnsubscribeDebugViewRequest request)
     {
-        _debugSubscribers.Remove(request.CorrelationId);
-        _streamManager?.RemoveSubscriber(Sender);
+        _debugSubscriberCorrelationIds.Remove(request.CorrelationId);
 
         _logger.LogDebug(
             "Debug view subscriber removed for {Instance}, correlationId={Id}",
@@ -479,10 +479,10 @@ public class InstanceActor : ReceiveActor
             alarmActor.Tell(changed);
         }
 
-        // Forward to debug subscribers
-        foreach (var sub in _debugSubscribers.Values)
+        // Forward to debug subscribers via SiteCommunicationActor → ClusterClient → central
+        foreach (var correlationId in _debugSubscriberCorrelationIds)
         {
-            sub.Tell(changed);
+            _siteCommActor?.Tell(new DebugStreamEvent(correlationId, changed));
         }
     }