feat(scadabridge): track scadabridge.site.connection.up over site-stream lifetime (balanced open/close)

src/ZB.MOM.WW.ScadaBridge.Communication/Grpc/SiteStreamGrpcServer.cs

@@ -7,6 +7,7 @@ using Microsoft.Extensions.Options;
 using ZB.MOM.WW.ScadaBridge.Commons.Entities.Audit;
 using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.Audit;
+using ZB.MOM.WW.ScadaBridge.Commons.Observability;
 using GrpcStatus = Grpc.Core.Status;
 
 namespace ZB.MOM.WW.ScadaBridge.Communication.Grpc;
@@ -264,6 +265,14 @@ public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
             "Stream {CorrelationId} started for {Instance} (subscription {SubscriptionId})",
             request.CorrelationId, request.InstanceUniqueName, subscriptionId);
 
+        // Telemetry follow-on: the connection is now fully established (Subscribe
+        // succeeded, so no leak via the catch above). Count it up here and balance
+        // it in the finally below so the scadabridge.site.connection.up gauge is
+        // decremented on EVERY exit path — normal completion, client-cancel /
+        // duplicate-replacement (OperationCanceledException), server shutdown
+        // (CancelAllStreams -> Cts.Cancel), and any other exception — guaranteeing
+        // exactly one Closed per Opened and a gauge that never drifts up.
+        ScadaBridgeTelemetry.SiteConnectionOpened();
         try
         {
             await foreach (var evt in channel.Reader.ReadAllAsync(streamCts.Token))
@@ -277,6 +286,7 @@ public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
         }
         finally
         {
+            ScadaBridgeTelemetry.SiteConnectionClosed();
             _streamSubscriber.RemoveSubscriber(relayActor);
             _actorSystem!.Stop(relayActor);
             channel.Writer.TryComplete();