fix(galaxy): unify IsConnected with _connected guard; AttachForTests marks connected (review)

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Runtime/GalaxyMxSession.cs

@@ -40,8 +40,12 @@ public sealed class GalaxyMxSession : IAsyncDisposable
         _logger = logger ?? NullLogger.Instance;
     }
 
-    /// <summary>Gets a value indicating whether the session is connected.</summary>
-    public bool IsConnected => _session is not null;
+    /// <summary>
+    ///     Gets a value indicating whether a session is currently established. Set <c>true</c> on a
+    ///     successful connect/attach and <c>false</c> after teardown/dispose — tracks the same
+    ///     <c>_connected</c> flag that <see cref="ConnectAsync"/> guards on, so the two never disagree.
+    /// </summary>
+    public bool IsConnected => _connected;
 
     /// <summary>
     ///     Server-side handle returned by MXAccess <c>Register</c>. Zero before
@@ -122,6 +126,7 @@ public sealed class GalaxyMxSession : IAsyncDisposable
         ObjectDisposedException.ThrowIf(_disposed, this);
         _session = session ?? throw new ArgumentNullException(nameof(session));
         _serverHandle = serverHandle;
+        _connected = true; // an attached session means connected — keeps IsConnected + the ConnectAsync no-op guard consistent.
     }
 
     /// <summary>