fix(dcl): stale MxGateway event-loop fault on a cancelled token no longer flaps the fresh connection (plan R2-03 T1)

src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/Adapters/MxGatewayDataConnection.cs

@@ -105,14 +105,16 @@ public class MxGatewayDataConnection : IDataConnection, IBrowsableDataConnection
 
         // Background event loop: route each value change to the matching subscription callback.
         _eventLoopCts = new CancellationTokenSource();
-        _ = Task.Run(() => RunEventLoopAsync(_eventLoopCts.Token));
+        var loopToken = _eventLoopCts.Token;   // capture NOW: the field may be replaced by a
+        var loopClient = _client;              // subsequent reconnect before Task.Run executes (N1)
+        _ = Task.Run(() => RunEventLoopAsync(loopClient, loopToken));
     }
 
-    private async Task RunEventLoopAsync(CancellationToken ct)
+    private async Task RunEventLoopAsync(IMxGatewayClient client, CancellationToken ct)
     {
         try
         {
-            await _client!.RunEventLoopAsync(update =>
+            await client.RunEventLoopAsync(update =>
             {
                 if (_tagToSub.TryGetValue(update.TagPath, out var subId) && _subs.TryGetValue(subId, out var s))
                     s.Callback(update.TagPath, new TagValue(update.Value, update.Quality, update.Timestamp));
@@ -122,6 +124,18 @@ public class MxGatewayDataConnection : IDataConnection, IBrowsableDataConnection
         {
             // Normal shutdown (DisconnectAsync / DisposeAsync cancelled the loop).
         }
+        catch (Exception ex) when (ct.IsCancellationRequested)
+        {
+            // Teardown fault of a superseded loop (N1): Cancel() is not synchronous with
+            // the loop's exit — a cancelled/disposed gRPC stream commonly surfaces as
+            // RpcException(StatusCode.Cancelled) (Grpc.Net default without
+            // ThrowOperationCanceledOnCancellation) or ObjectDisposedException from the
+            // concurrent DisposeAsync, milliseconds AFTER ConnectAsync has already reset
+            // _disconnectFired. Any fault on a cancelled token is normal shutdown;
+            // raising Disconnected here would flap the NEW healthy session.
+            _logger.LogDebug(ex,
+                "MxGateway event loop faulted after cancellation — superseded loop teardown; not signalling disconnect");
+        }
         catch (Exception ex)
         {
             _logger.LogWarning(ex, "MxGateway event stream faulted; signalling disconnect");