feat(comm): ack site health reports end-to-end (SiteHealthReportAck, additive contract)

src/ZB.MOM.WW.ScadaBridge.Communication/Actors/SiteCommunicationActor.cs

@@ -390,11 +390,28 @@ public class SiteCommunicationActor : ReceiveActor, IWithTimers
         // Internal: send heartbeat tick
         Receive<SendHeartbeat>(_ => SendHeartbeatToCentral());
 
-        // Internal: forward health report to central
+        // Internal: forward health report to central. The original Sender (the
+        // AkkaHealthReportTransport's Ask) is forwarded as the ClusterClient.Send
+        // sender so the central SiteHealthReportAck routes straight back to the
+        // waiting Ask — making report delivery observable end-to-end (review 01
+        // [Medium]). Mirrors the NotificationSubmit ack pattern above.
         Receive<SiteHealthReport>(msg =>
         {
-            _centralClient?.Tell(
-                new ClusterClient.Send("/user/central-communication", msg), Self);
+            if (_centralClient == null)
+            {
+                // No ClusterClient registered yet. A non-accepted ack makes the
+                // sender's counter-restore path treat this tick as a loss.
+                _log.Warning(
+                    "Cannot forward SiteHealthReport #{0} — no central ClusterClient registered",
+                    msg.SequenceNumber);
+                Sender.Tell(new SiteHealthReportAck(
+                    msg.SiteId, msg.SequenceNumber, Accepted: false,
+                    Error: "Central ClusterClient not registered"));
+                return;
+            }
+
+            _centralClient.Tell(
+                new ClusterClient.Send("/user/central-communication", msg), Sender);
         });
 
     }