feat(notification-outbox): route NotificationSubmit to the outbox actor

src/ScadaLink.Communication/Actors/CentralCommunicationActor.cs

@@ -7,6 +7,7 @@ using Microsoft.Extensions.DependencyInjection;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Messages.Communication;
 using ScadaLink.Commons.Messages.Health;
+using ScadaLink.Commons.Messages.Notification;
 using ScadaLink.HealthMonitoring;
 
 namespace ScadaLink.Communication.Actors;
@@ -66,6 +67,15 @@ public class CentralCommunicationActor : ReceiveActor
 
     private ICancelable? _refreshSchedule;
 
+    /// <summary>
+    /// Proxy <see cref="IActorRef"/> for the central NotificationOutboxActor cluster singleton.
+    /// Set via <see cref="RegisterNotificationOutbox"/> — the Host creates the singleton proxy
+    /// after this actor and registers it (mirrors how the site-side actor receives its
+    /// runtime <see cref="IActorRef"/>s). Null until registration completes; a notification
+    /// arriving before then is rejected with a non-accepted ack so the site retries.
+    /// </summary>
+    private IActorRef? _notificationOutboxProxy;
+
     /// <summary>
     /// DistributedPubSub topic used to fan health reports out to the peer
     /// central node so both per-node aggregators stay in sync. See
@@ -105,6 +115,61 @@ public class CentralCommunicationActor : ReceiveActor
         // Route enveloped messages to sites
         Receive<SiteEnvelope>(HandleSiteEnvelope);
 
+        // Notification Outbox: the Host registers the outbox singleton proxy after this
+        // actor is created (the proxy cannot exist before this actor's construction).
+        Receive<RegisterNotificationOutbox>(msg =>
+        {
+            _notificationOutboxProxy = msg.OutboxProxy;
+            _log.Info("Registered notification outbox proxy");
+        });
+
+        // Notification Outbox ingest: a site forwards a buffered NotificationSubmit to the
+        // central cluster via ClusterClient. Forward to the outbox proxy so the original
+        // Sender (the site's ClusterClient path) is preserved and the NotificationSubmitAck
+        // routes straight back to the site.
+        Receive<NotificationSubmit>(HandleNotificationSubmit);
+
+        // Notification Outbox status query: forward to the outbox proxy, preserving Sender
+        // so the NotificationStatusResponse routes back to the querying site.
+        Receive<NotificationStatusQuery>(HandleNotificationStatusQuery);
+
+    }
+
+    private void HandleNotificationSubmit(NotificationSubmit msg)
+    {
+        if (_notificationOutboxProxy == null)
+        {
+            // No outbox proxy registered yet. A non-accepted ack makes the site's
+            // Store-and-Forward forwarder treat this as transient and retry later.
+            _log.Warning(
+                "Cannot route NotificationSubmit {0} — notification outbox not available",
+                msg.NotificationId);
+            Sender.Tell(new NotificationSubmitAck(
+                msg.NotificationId, Accepted: false, Error: "notification outbox not available"));
+            return;
+        }
+
+        _log.Debug("Routing NotificationSubmit {0} to the notification outbox", msg.NotificationId);
+        _notificationOutboxProxy.Forward(msg);
+    }
+
+    private void HandleNotificationStatusQuery(NotificationStatusQuery msg)
+    {
+        if (_notificationOutboxProxy == null)
+        {
+            // No outbox proxy registered yet. Reply Found: false so the querying site
+            // falls back to its local Store-and-Forward buffer to resolve the status.
+            _log.Warning(
+                "Cannot route NotificationStatusQuery {0} — notification outbox not available",
+                msg.NotificationId);
+            Sender.Tell(new NotificationStatusResponse(
+                msg.CorrelationId, Found: false, Status: "Unknown",
+                RetryCount: 0, LastError: null, DeliveredAt: null));
+            return;
+        }
+
+        _log.Debug("Routing NotificationStatusQuery {0} to the notification outbox", msg.NotificationId);
+        _notificationOutboxProxy.Forward(msg);
     }
 
     private void HandleHeartbeat(HeartbeatMessage heartbeat)
@@ -391,3 +456,11 @@ internal record SiteAddressCacheLoaded(Dictionary<string, List<string>> SiteCont
 /// due to site disconnection (WP-5).
 /// </summary>
 public record DebugStreamTerminated(string SiteId, string CorrelationId);
+
+/// <summary>
+/// Registers the central NotificationOutboxActor singleton proxy with the
+/// <see cref="CentralCommunicationActor"/> so site-forwarded <see cref="NotificationSubmit"/>
+/// and <see cref="NotificationStatusQuery"/> messages can be routed to it. Sent by the Host
+/// after the outbox singleton proxy is created.
+/// </summary>
+public record RegisterNotificationOutbox(IActorRef OutboxProxy);