fix(dcl): MxGateway adapter treats a graceful end of the event stream as a disconnect — a dashboard 'close session' (or graceful gateway shutdown) completes the stream with OK, leaving the adapter Connected on a dead session: values frozen at last GOOD quality, every write 'Session … was not found' until restart (QA vq03 Z28061 MoveIn, 2026-08-20). Pinned: signals once while connected, silent for superseded loops / own teardown

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

@@ -182,6 +182,23 @@ public class MxGatewayDataConnection
                 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));
             }, ct);
+
+            // A GRACEFUL end of the event stream (OK status, no fault) while we did not ask
+            // for it means the gateway closed the session underneath us — a dashboard
+            // "close session", or a graceful gateway shutdown, both complete the per-session
+            // subscriber channels with no error (CompleteAllSubscribers(error: null)).
+            // Before this branch existed the loop simply returned: the adapter stayed
+            // Connected, every subscribed value froze at its last GOOD quality, and every
+            // write hit the dead session ("Session … was not found") until a process
+            // restart — QA incident 2026-08-20, vq03 Z28061 MoveIn, one hour of silent loss.
+            // Same bug class as SiteStreamGrpcClient's graceful-completion reconnect
+            // (commit 34a3f4bb). A cancelled token is our own teardown, never a disconnect.
+            if (!ct.IsCancellationRequested)
+            {
+                _logger.LogWarning(
+                    "MxGateway event stream ended without a fault while connected — the gateway closed the session; signalling disconnect");
+                RaiseDisconnected();
+            }
         }
         catch (OperationCanceledException)
         {