diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs
index 1bcc63b6..58412d0f 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs
@@ -282,15 +282,17 @@ public sealed class GalaxyDriver
     }
 
     /// <summary>
-    ///     Reopen callback for <see cref="ReconnectSupervisor"/>: re-Register the gw session.
-    ///     If the session never connected, this is a fresh ConnectAsync; otherwise it's a
-    ///     reconnect against the existing client.
+    ///     Reopen callback for <see cref="ReconnectSupervisor"/>: recreate the gw session. After a
+    ///     gateway restart the existing session handle is faulted / stale but non-null, so a plain
+    ///     <c>ConnectAsync</c> would no-op and the supervisor would loop forever replaying against a
+    ///     dead session. <see cref="GalaxyMxSession.RecreateAsync"/> disposes the stale session +
+    ///     owned client and rebuilds, so a never-connected session still opens fresh.
     /// </summary>
     private async Task ReopenAsync(CancellationToken cancellationToken)
     {
         if (_ownedMxSession is null) return;
         var clientOptions = BuildClientOptions(_options.Gateway);
-        await _ownedMxSession.ConnectAsync(clientOptions, cancellationToken).ConfigureAwait(false);
+        await _ownedMxSession.RecreateAsync(clientOptions, cancellationToken).ConfigureAwait(false);
     }
 
     /// <summary>
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Runtime/GalaxyMxSession.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Runtime/GalaxyMxSession.cs
index 7913c69c..d48d3528 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Runtime/GalaxyMxSession.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Runtime/GalaxyMxSession.cs
@@ -28,6 +28,7 @@ public sealed class GalaxyMxSession : IAsyncDisposable
     private MxGatewayClient? _ownedClient;
     private MxGatewaySession? _session;
     private int _serverHandle;
+    private bool _connected;
     private bool _disposed;
 
     /// <summary>Initializes a new instance of the GalaxyMxSession class.</summary>
@@ -48,24 +49,65 @@ public sealed class GalaxyMxSession : IAsyncDisposable
     /// </summary>
     public int ServerHandle => _serverHandle;
 
+    /// <summary>
+    ///     Test seam — when set, replaces the real "open session + register" work so unit tests can
+    ///     exercise the connect / recreate orchestration without a live gateway (the SDK session/client
+    ///     types are sealed + internal-ctor and cannot be faked). Null in production = real gateway path.
+    /// </summary>
+    internal Func<CancellationToken, Task>? OpenAndRegisterOverrideForTests { get; set; }
+
     /// <summary>
     ///     Connect the underlying gateway client + open an MXAccess session + register the
-    ///     configured client name. Idempotent — second calls are no-ops while
-    ///     <see cref="IsConnected"/> is true.
+    ///     configured client name. Idempotent — second calls are no-ops while a connect has
+    ///     already succeeded. Use <see cref="RecreateAsync"/> to force a rebuild after the
+    ///     gateway restarts and leaves a faulted / stale session handle.
     /// </summary>
     /// <param name="clientOptions">The MX gateway client options.</param>
     /// <param name="cancellationToken">The cancellation token.</param>
     public async Task ConnectAsync(MxGatewayClientOptions clientOptions, CancellationToken cancellationToken)
     {
         ObjectDisposedException.ThrowIf(_disposed, this);
-        if (_session is not null) return;
+        if (_connected) return;
 
-        _ownedClient = MxGatewayClient.Create(clientOptions);
-        _session = await _ownedClient.OpenSessionAsync(cancellationToken: cancellationToken).ConfigureAwait(false);
-        _serverHandle = await _session.RegisterAsync(_options.ClientName, cancellationToken).ConfigureAwait(false);
-        _logger.LogInformation(
-            "GalaxyMxSession connected — clientName={ClientName} serverHandle={Handle}",
-            _options.ClientName, _serverHandle);
+        try
+        {
+            if (OpenAndRegisterOverrideForTests is not null)
+            {
+                await OpenAndRegisterOverrideForTests(cancellationToken).ConfigureAwait(false);
+            }
+            else
+            {
+                _ownedClient = MxGatewayClient.Create(clientOptions);
+                _session = await _ownedClient.OpenSessionAsync(cancellationToken: cancellationToken).ConfigureAwait(false);
+                _serverHandle = await _session.RegisterAsync(_options.ClientName, cancellationToken).ConfigureAwait(false);
+            }
+
+            _connected = true;
+            _logger.LogInformation(
+                "GalaxyMxSession connected — clientName={ClientName} serverHandle={Handle}",
+                _options.ClientName, _serverHandle);
+        }
+        catch
+        {
+            // A partial open (e.g. OpenSession succeeded but Register threw) must not leave a half-open
+            // handle that blocks the next reconnect. Tear the partial state down so a retry rebuilds cleanly.
+            await TeardownSessionAsync().ConfigureAwait(false);
+            throw;
+        }
+    }
+
+    /// <summary>
+    ///     Disposes the current (faulted / stale) session + owned client and rebuilds. Use this on
+    ///     reconnect: <see cref="ConnectAsync"/> alone no-ops while a (possibly dead) session handle is
+    ///     still present, so the supervisor's reopen must route through here to actually re-establish.
+    /// </summary>
+    /// <param name="clientOptions">The MX gateway client options.</param>
+    /// <param name="cancellationToken">The cancellation token.</param>
+    public async Task RecreateAsync(MxGatewayClientOptions clientOptions, CancellationToken cancellationToken)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        await TeardownSessionAsync().ConfigureAwait(false);
+        await ConnectAsync(clientOptions, cancellationToken).ConfigureAwait(false);
     }
 
     /// <summary>
@@ -93,19 +135,31 @@ public sealed class GalaxyMxSession : IAsyncDisposable
     {
         if (_disposed) return;
         _disposed = true;
+        await TeardownSessionAsync().ConfigureAwait(false);
+    }
+
+    /// <summary>
+    ///     Resets the connect flag and best-effort disposes + nulls the owned session and client.
+    ///     Shared by <see cref="DisposeAsync"/> (final teardown) and <see cref="RecreateAsync"/> /
+    ///     the partial-open recovery path (rebuild teardown) — it does NOT set <c>_disposed</c>, so
+    ///     a torn-down session can be re-opened.
+    /// </summary>
+    private async Task TeardownSessionAsync()
+    {
+        _connected = false;
 
         if (_session is not null)
         {
             try { await _session.DisposeAsync().ConfigureAwait(false); }
             catch (Exception ex) { _logger.LogWarning(ex, "GalaxyMxSession session dispose failed (best-effort)"); }
+            _session = null;
         }
-        _session = null;
 
         if (_ownedClient is not null)
         {
             try { await _ownedClient.DisposeAsync().ConfigureAwait(false); }
             catch (Exception ex) { _logger.LogWarning(ex, "GalaxyMxSession client dispose failed (best-effort)"); }
+            _ownedClient = null;
         }
-        _ownedClient = null;
     }
 }
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/Runtime/GalaxyMxSessionReconnectTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/Runtime/GalaxyMxSessionReconnectTests.cs
new file mode 100644
index 00000000..b1e689eb
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/Runtime/GalaxyMxSessionReconnectTests.cs
@@ -0,0 +1,106 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Config;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Runtime;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests.Runtime;
+
+/// <summary>
+///     Connect / recreate orchestration tests for <see cref="GalaxyMxSession"/>. The SDK
+///     session/client types are sealed with internal ctors and cannot be faked, so these
+///     drive the open body through the <c>OpenAndRegisterOverrideForTests</c> seam. The
+///     core regression guard is <see cref="Recreate_after_connect_opens_a_fresh_session"/>:
+///     a stale-session reconnect must rebuild rather than no-op (the gateway-restart bug).
+/// </summary>
+public sealed class GalaxyMxSessionReconnectTests
+{
+    private static GalaxyMxAccessOptions MinimalOptions() => new(ClientName: "OtOpcUaTest");
+
+    private static GalaxyMxSession NewSession() => new(MinimalOptions());
+
+    /// <summary>A second <c>ConnectAsync</c> while connected must be a no-op (idempotent guard).</summary>
+    [Fact]
+    public async Task Connect_then_connect_again_is_a_noop()
+    {
+        var session = NewSession();
+        var openCount = 0;
+        session.OpenAndRegisterOverrideForTests = _ =>
+        {
+            openCount++;
+            return Task.CompletedTask;
+        };
+
+        await session.ConnectAsync(null!, CancellationToken.None);
+        openCount.ShouldBe(1);
+
+        await session.ConnectAsync(null!, CancellationToken.None);
+        openCount.ShouldBe(1);
+    }
+
+    /// <summary>
+    ///     The regression guard for the gateway-restart bug: <c>RecreateAsync</c> must bypass
+    ///     the no-op guard and re-run the open body even though a (stale) session is present.
+    /// </summary>
+    [Fact]
+    public async Task Recreate_after_connect_opens_a_fresh_session()
+    {
+        var session = NewSession();
+        var openCount = 0;
+        session.OpenAndRegisterOverrideForTests = _ =>
+        {
+            openCount++;
+            return Task.CompletedTask;
+        };
+
+        await session.ConnectAsync(null!, CancellationToken.None);
+        openCount.ShouldBe(1);
+
+        await session.RecreateAsync(null!, CancellationToken.None);
+        openCount.ShouldBe(2);
+    }
+
+    /// <summary><c>RecreateAsync</c> on a never-connected session still opens (teardown is a no-op first).</summary>
+    [Fact]
+    public async Task Recreate_when_never_connected_still_opens()
+    {
+        var session = NewSession();
+        var openCount = 0;
+        session.OpenAndRegisterOverrideForTests = _ =>
+        {
+            openCount++;
+            return Task.CompletedTask;
+        };
+
+        await session.RecreateAsync(null!, CancellationToken.None);
+        openCount.ShouldBe(1);
+    }
+
+    /// <summary>
+    ///     A failed first connect must not leave <c>_connected</c> set — the next attempt has
+    ///     to reach the open body again (partial-open teardown).
+    /// </summary>
+    [Fact]
+    public async Task Connect_failure_is_not_left_half_open()
+    {
+        var session = NewSession();
+        var openCount = 0;
+        session.OpenAndRegisterOverrideForTests = _ =>
+        {
+            // Throw on the first attempt, succeed on the second.
+            if (openCount++ == 0)
+            {
+                throw new InvalidOperationException("simulated open failure");
+            }
+
+            return Task.CompletedTask;
+        };
+
+        await Should.ThrowAsync<InvalidOperationException>(
+            async () => await session.ConnectAsync(null!, CancellationToken.None));
+        openCount.ShouldBe(1);
+
+        // The failed first attempt must not have latched _connected — the retry reaches the body.
+        await session.ConnectAsync(null!, CancellationToken.None);
+        openCount.ShouldBe(2);
+    }
+}