diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipReinitializeReleasesStateTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipReinitializeReleasesStateTests.cs
index ebee2056..b7891d27 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipReinitializeReleasesStateTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipReinitializeReleasesStateTests.cs
@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
@@ -8,7 +9,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
 ///     orphaned the previous state's probe loop + handles. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class AbCipReinitializeReleasesStateTests
+public sealed class AbCipReinitializeReleasesStateTests(ITestOutputHelper output)
 {
     /// <summary>Initialize twice: the first state's probe loop has stopped and its probe handle is disposed.</summary>
     [Fact]
@@ -27,28 +28,94 @@ public sealed class AbCipReinitializeReleasesStateTests
                 ProbeTagPath = "@raw_cpu_type",
             },
         }, "drv-reinit", factory);
-        await drv.InitializeAsync("{}", CancellationToken.None);
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var first = drv.GetDeviceState(host)!;
-        // Positive control: the first probe loop is running and has initialised its runtime.
+            var first = drv.GetDeviceState(host)!;
+            // Positive control: the first probe loop is running and has initialised its runtime.
+            var deadline = DateTime.UtcNow.AddSeconds(5);
+            while (!(factory.Tags.TryGetValue("@raw_cpu_type", out var t) && t.InitializeCount > 0))
+            {
+                if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never started");
+                await Task.Delay(10);
+            }
+            var firstTag = factory.Tags["@raw_cpu_type"];
+            var firstLoop = first.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            firstTag.Disposed.ShouldBeFalse();
+
+            await drv.InitializeAsync("{}", CancellationToken.None);
+
+            firstLoop.IsCompleted.ShouldBeTrue(); // joined
+            firstTag.Disposed.ShouldBeTrue();
+            drv.GetDeviceState(host).ShouldNotBeSameAs(first);
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"AbCip SecondInitialize cleanup failed: {failure}"));
+    }
+
+    /// <summary>Failure after a live first or replacement state must release both owned resources.</summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task Body_failure_releases_live_probe_resources(bool afterReplacement)
+    {
+        const string host = "ab://10.0.0.5/1,0";
+        var factory = new FakeAbCipTagFactory();
+        var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(host)],
+            Probe = new AbCipProbeOptions
+            {
+                Enabled = true,
+                Interval = TimeSpan.FromMilliseconds(20),
+                Timeout = TimeSpan.FromMilliseconds(200),
+                ProbeTagPath = "@raw_cpu_type",
+            },
+        }, "drv-reinit", factory);
+        Task? firstLoop = null, secondLoop = null;
+        FakeAbCipTag? firstTag = null, secondTag = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
+            await WaitForProbeAsync(() => factory.Tags.TryGetValue("@raw_cpu_type", out var tag) && tag.InitializeCount > 0);
+            firstTag = factory.Tags["@raw_cpu_type"];
+            firstLoop = drv.GetDeviceState(host)!.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            firstTag.Disposed.ShouldBeFalse();
+            if (afterReplacement)
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                await WaitForProbeAsync(() => factory.Tags.TryGetValue("@raw_cpu_type", out var tag) && !ReferenceEquals(tag, firstTag) && tag.InitializeCount > 0);
+                secondTag = factory.Tags["@raw_cpu_type"];
+                secondLoop = drv.GetDeviceState(host)!.ProbeTask;
+                _ = secondLoop.ShouldNotBeNull();
+                secondLoop!.IsCompleted.ShouldBeFalse();
+            }
+            throw sentinel;
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"AbCip failure fixture cleanup failed: {failure}")));
+        actual.ShouldBeSameAs(sentinel);
+        firstLoop!.IsCompleted.ShouldBeTrue();
+        firstTag!.Disposed.ShouldBeTrue();
+        if (afterReplacement)
+        {
+            secondLoop!.IsCompleted.ShouldBeTrue();
+            secondTag!.Disposed.ShouldBeTrue();
+        }
+    }
+
+    private static async Task WaitForProbeAsync(Func<bool> condition)
+    {
         var deadline = DateTime.UtcNow.AddSeconds(5);
-        while (!(factory.Tags.TryGetValue("@raw_cpu_type", out var t) && t.InitializeCount > 0))
+        while (!condition())
         {
             if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never started");
             await Task.Delay(10);
         }
-        var firstTag = factory.Tags["@raw_cpu_type"];
-        var firstLoop = first.ProbeTask;
-        firstLoop.ShouldNotBeNull();
-        firstLoop!.IsCompleted.ShouldBeFalse();
-        firstTag.Disposed.ShouldBeFalse();
-
-        await drv.InitializeAsync("{}", CancellationToken.None);
-
-        firstLoop.IsCompleted.ShouldBeTrue(); // joined
-        firstTag.Disposed.ShouldBeTrue();
-        drv.GetDeviceState(host).ShouldNotBeSameAs(first);
-
-        await drv.ShutdownAsync(CancellationToken.None);
     }
+
 }
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/FixtureCleanupTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/FixtureCleanupTests.cs
new file mode 100644
index 00000000..582af8b7
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/FixtureCleanupTests.cs
@@ -0,0 +1,92 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Tests;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class FixtureCleanupTests
+{
+    [Fact]
+    public async Task Successful_body_runs_one_awaited_cleanup()
+    {
+        var calls = 0;
+        var release = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var run = FixtureCleanup.RunAsync(() => Task.CompletedTask, async () =>
+        {
+            calls++;
+            await release.Task;
+        }, _ => throw new Exception("unexpected report"));
+
+        run.IsCompleted.ShouldBeFalse();
+        release.SetResult();
+        await run;
+        calls.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Body_fault_remains_same_exception_and_original_throwing_stack()
+    {
+        var primary = new InvalidOperationException("body");
+        var cleanupCalls = 0;
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(
+            () => ThrowFromBody(primary),
+            () => { cleanupCalls++; return Task.CompletedTask; },
+            _ => throw new Exception("unexpected report")));
+
+        actual.ShouldBeSameAs(primary);
+        actual.StackTrace.ShouldNotBeNull().ShouldContain(nameof(ThrowFromBody));
+        cleanupCalls.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Cleanup_only_fault_is_thrown_exactly()
+    {
+        var cleanup = new ApplicationException("cleanup");
+        var actual = await Should.ThrowAsync<ApplicationException>(() => FixtureCleanup.RunAsync(
+            () => Task.CompletedTask,
+            () => Task.FromException(cleanup),
+            _ => throw new Exception("unexpected report")));
+        actual.ShouldBeSameAs(cleanup);
+    }
+
+    [Fact]
+    public async Task Both_faults_preserve_primary_and_record_secondary_once()
+    {
+        var primary = new InvalidOperationException("body");
+        var cleanup = new ApplicationException("cleanup");
+        var reported = new List<Exception>();
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(
+            () => ThrowFromBody(primary),
+            () => Task.FromException(cleanup),
+            reported.Add));
+
+        actual.ShouldBeSameAs(primary);
+        actual.StackTrace.ShouldNotBeNull().ShouldContain(nameof(ThrowFromBody));
+        actual.Data[FixtureCleanup.SecondaryExceptionKey].ShouldBeSameAs(cleanup);
+        reported.Count.ShouldBe(1);
+        reported[0].ShouldBeSameAs(cleanup);
+    }
+
+    [Fact]
+    public async Task Reporting_fault_does_not_replace_primary()
+    {
+        var primary = new InvalidOperationException("body");
+        var cleanup = new ApplicationException("cleanup");
+        var reportCalls = 0;
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(
+            () => ThrowFromBody(primary),
+            () => Task.FromException(cleanup),
+            _ => { reportCalls++; throw new Exception("report"); }));
+
+        actual.ShouldBeSameAs(primary);
+        actual.Data[FixtureCleanup.SecondaryExceptionKey].ShouldBeSameAs(cleanup);
+        reportCalls.ShouldBe(1);
+    }
+
+    private static async Task ThrowFromBody(Exception failure)
+    {
+        await Task.Yield();
+        throw failure;
+    }
+}
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests.csproj b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests.csproj
index 38c3d151..898e7284 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests.csproj
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests.csproj
@@ -38,4 +38,7 @@
         <Compile Include="..\ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Tests\Fakes\FakeCipTarget.cs" Link="Fakes\FakeCipTarget.cs" />
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReinitializeReleasesStateTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReinitializeReleasesStateTests.cs
index 85f3d1b5..f2d6b0df 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReinitializeReleasesStateTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReinitializeReleasesStateTests.cs
@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.PlcFamilies;
 
@@ -10,7 +11,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests;
 ///     probe loop + runtime. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class AbLegacyReinitializeReleasesStateTests
+public sealed class AbLegacyReinitializeReleasesStateTests(ITestOutputHelper output)
 {
     /// <summary>Initialize twice: the first state's probe loop has stopped and its probe runtime is disposed.</summary>
     [Fact]
@@ -23,28 +24,88 @@ public sealed class AbLegacyReinitializeReleasesStateTests
             Devices = [new AbLegacyDeviceOptions(host, AbLegacyPlcFamily.Slc500)],
             Probe = new AbLegacyProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), ProbeAddress = "S:0" },
         }, "drv-reinit", factory);
-        await drv.InitializeAsync("{}", CancellationToken.None);
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var first = drv.GetDeviceState(host)!;
-        // Positive control: the first state's probe loop is running and has created + initialised its runtime.
+            var first = drv.GetDeviceState(host)!;
+            // Positive control: the first state's probe loop is running and has created + initialised its runtime.
+            var deadline = DateTime.UtcNow.AddSeconds(5);
+            while (!(factory.Tags.TryGetValue("S:0", out var t) && t.InitializeCount > 0))
+            {
+                if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never started");
+                await Task.Delay(10);
+            }
+            var firstTag = factory.Tags["S:0"];
+            var firstLoop = first.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            firstTag.Disposed.ShouldBeFalse();
+
+            await drv.InitializeAsync("{}", CancellationToken.None);
+
+            firstLoop.IsCompleted.ShouldBeTrue(); // joined
+            firstTag.Disposed.ShouldBeTrue();
+            drv.GetDeviceState(host).ShouldNotBeSameAs(first);
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"AbLegacy SecondInitialize cleanup failed: {failure}"));
+    }
+
+    /// <summary>Failure after a live first or replacement state must release both owned resources.</summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task Body_failure_releases_live_probe_resources(bool afterReplacement)
+    {
+        const string host = "ab://10.0.0.5/1,0";
+        var factory = new FakeAbLegacyTagFactory();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions(host, AbLegacyPlcFamily.Slc500)],
+            Probe = new AbLegacyProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), ProbeAddress = "S:0" },
+        }, "drv-reinit", factory);
+        Task? firstLoop = null, secondLoop = null;
+        FakeAbLegacyTag? firstTag = null, secondTag = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
+            await WaitForProbeAsync(() => factory.Tags.TryGetValue("S:0", out var tag) && tag.InitializeCount > 0);
+            firstTag = factory.Tags["S:0"];
+            firstLoop = drv.GetDeviceState(host)!.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            firstTag.Disposed.ShouldBeFalse();
+            if (afterReplacement)
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                await WaitForProbeAsync(() => factory.Tags.TryGetValue("S:0", out var tag) && !ReferenceEquals(tag, firstTag) && tag.InitializeCount > 0);
+                secondTag = factory.Tags["S:0"];
+                secondLoop = drv.GetDeviceState(host)!.ProbeTask;
+                _ = secondLoop.ShouldNotBeNull();
+                secondLoop!.IsCompleted.ShouldBeFalse();
+            }
+            throw sentinel;
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"AbLegacy failure fixture cleanup failed: {failure}")));
+        actual.ShouldBeSameAs(sentinel);
+        firstLoop!.IsCompleted.ShouldBeTrue();
+        firstTag!.Disposed.ShouldBeTrue();
+        if (afterReplacement)
+        {
+            secondLoop!.IsCompleted.ShouldBeTrue();
+            secondTag!.Disposed.ShouldBeTrue();
+        }
+    }
+
+    private static async Task WaitForProbeAsync(Func<bool> condition)
+    {
         var deadline = DateTime.UtcNow.AddSeconds(5);
-        while (!(factory.Tags.TryGetValue("S:0", out var t) && t.InitializeCount > 0))
+        while (!condition())
         {
             if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never started");
             await Task.Delay(10);
         }
-        var firstTag = factory.Tags["S:0"];
-        var firstLoop = first.ProbeTask;
-        firstLoop.ShouldNotBeNull();
-        firstLoop!.IsCompleted.ShouldBeFalse();
-        firstTag.Disposed.ShouldBeFalse();
-
-        await drv.InitializeAsync("{}", CancellationToken.None);
-
-        firstLoop.IsCompleted.ShouldBeTrue(); // joined
-        firstTag.Disposed.ShouldBeTrue();
-        drv.GetDeviceState(host).ShouldNotBeSameAs(first);
-
-        await drv.ShutdownAsync(CancellationToken.None);
     }
+
 }
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests.csproj b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests.csproj
index ae370b85..cc9bbc8c 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests.csproj
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests.csproj
@@ -38,4 +38,7 @@
         <None Include="..\ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Tests\Captures\*.hex" Link="Captures\%(Filename)%(Extension)" CopyToOutputDirectory="PreserveNewest"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasReinitializeReleasesStateTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasReinitializeReleasesStateTests.cs
index e1687105..2e3eb6b2 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasReinitializeReleasesStateTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasReinitializeReleasesStateTests.cs
@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
 
@@ -10,7 +11,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
 ///     probe loop + client. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class FocasReinitializeReleasesStateTests
+public sealed class FocasReinitializeReleasesStateTests(ITestOutputHelper output)
 {
     /// <summary>Initialize twice: the first state's probe loop has finished and its client is disposed.</summary>
     [Fact]
@@ -25,25 +26,78 @@ public sealed class FocasReinitializeReleasesStateTests
             Probe = new FocasProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), Timeout = TimeSpan.FromSeconds(2) },
         };
         var drv = new FocasDriver(options, "focas-reinit", factory);
-        await drv.InitializeAsync("{}", CancellationToken.None);
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var first = drv.GetDeviceState(host)!;
-        // Positive control: the first state's probe loop is demonstrably running and holds a live client.
-        await WaitUntilAsync(() => factory.Clients.Count > 0 && factory.Clients[0].IsConnected);
-        var firstLoop = first.ProbeTask;
-        firstLoop.ShouldNotBeNull();
-        firstLoop!.IsCompleted.ShouldBeFalse();
-        var firstClient = factory.Clients[0];
+            var first = drv.GetDeviceState(host)!;
+            // Positive control: the first state's probe loop is demonstrably running and holds a live client.
+            await WaitUntilAsync(() => factory.Clients.Count > 0 && factory.Clients[0].IsConnected);
+            var firstLoop = first.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            var firstClient = factory.Clients[0];
 
-        await drv.InitializeAsync("{}", CancellationToken.None);
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        firstLoop.IsCompleted.ShouldBeTrue(); // joined
-        firstClient.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            firstLoop.IsCompleted.ShouldBeTrue(); // joined
+            firstClient.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            firstClient.IsConnected.ShouldBeFalse();
+            drv.GetDeviceState(host).ShouldNotBeSameAs(first);
+            _ = drv.GetDeviceState(host)!.ProbeTask.ShouldNotBeNull(); // the new state is running
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"FOCAS SecondInitialize cleanup failed: {failure}"));
+    }
+
+
+    /// <summary>Failure after a live first or replacement state must release both owned resources.</summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task Body_failure_releases_live_probe_resources(bool afterReplacement)
+    {
+        const string host = "focas://10.0.0.5:8193";
+        var factory = new FakeFocasClientFactory();
+        var options = new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions(host)],
+            RawTags = [FocasRawTags.Entry(new FocasTagDefinition("R", host, "R100", FocasDataType.Byte))],
+            Probe = new FocasProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), Timeout = TimeSpan.FromSeconds(2) },
+        };
+        var drv = new FocasDriver(options, "focas-reinit", factory);
+        Task? firstLoop = null, secondLoop = null;
+        FakeFocasClient? firstClient = null, secondClient = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
+            await WaitUntilAsync(() => factory.Clients.Count > 0 && factory.Clients[0].IsConnected);
+            firstClient = factory.Clients[0];
+            firstLoop = drv.GetDeviceState(host)!.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            if (afterReplacement)
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                await WaitUntilAsync(() => factory.Clients.Count > 1 && factory.Clients[1].IsConnected);
+                secondClient = factory.Clients[1];
+                secondLoop = drv.GetDeviceState(host)!.ProbeTask;
+                _ = secondLoop.ShouldNotBeNull();
+                secondLoop!.IsCompleted.ShouldBeFalse();
+            }
+            throw sentinel;
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"FOCAS failure fixture cleanup failed: {failure}")));
+        actual.ShouldBeSameAs(sentinel);
+        firstLoop!.IsCompleted.ShouldBeTrue();
+        firstClient!.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
         firstClient.IsConnected.ShouldBeFalse();
-        drv.GetDeviceState(host).ShouldNotBeSameAs(first);
-        drv.GetDeviceState(host)!.ProbeTask.ShouldNotBeNull(); // the new state is running
-
-        await drv.ShutdownAsync(CancellationToken.None);
+        if (afterReplacement)
+        {
+            secondLoop!.IsCompleted.ShouldBeTrue();
+            secondClient!.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            secondClient.IsConnected.ShouldBeFalse();
+        }
     }
 
     private static async Task WaitUntilAsync(Func<bool> cond)
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests.csproj b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests.csproj
index c4f4be54..d8351579 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests.csproj
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests.csproj
@@ -34,4 +34,7 @@
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.FOCAS\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverLifecycleTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverLifecycleTests.cs
index 857f606d..3e07df40 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverLifecycleTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverLifecycleTests.cs
@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 
@@ -16,7 +17,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests;
 ///     keeps talking to the old Agent, and a cache flush that wedges browse. Each of those is a
 ///     defect the happy-path assertions alone would pass straight over.
 /// </remarks>
-public sealed class MTConnectDriverLifecycleTests
+public sealed class MTConnectDriverLifecycleTests(ITestOutputHelper output)
 {
     private const string AgentUri = "http://fixture-agent:5000";
 
@@ -598,18 +599,79 @@ public sealed class MTConnectDriverLifecycleTests
     // same "browse must not be left permanently empty" obligation.
 
     [Fact]
-    public void Dropping_the_probe_cache_keeps_the_observation_index()
+    public async Task Dropping_the_probe_cache_keeps_the_observation_index()
     {
-        var (driver, _) = InitializedDriverAsync().GetAwaiter().GetResult();
+        var (driver, _) = NewDriver();
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await driver.InitializeAsync("{}", CancellationToken.None);
 
-        driver.InvalidateProbeModel();
+            driver.InvalidateProbeModel();
 
-        driver.CachedProbeModel.ShouldBeNull();
+            driver.CachedProbeModel.ShouldBeNull();
 
-        // The index is required for correctness (it IS the read surface) — never flushable.
-        driver.ObservationIndex.Count.ShouldBe(FixtureDataItemCount);
-        driver.ObservationIndex.Get("dev1_pos").StatusCode.ShouldBe(0u);
-        driver.GetHealth().State.ShouldBe(DriverState.Healthy);
+            // The index is required for correctness (it IS the read surface) — never flushable.
+            driver.ObservationIndex.Count.ShouldBe(FixtureDataItemCount);
+            driver.ObservationIndex.Get("dev1_pos").StatusCode.ShouldBe(0u);
+            driver.GetHealth().State.ShouldBe(DriverState.Healthy);
+        }, () => driver.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"MTConnect cache drop cleanup failed: {failure}"));
+    }
+
+    [Fact]
+    public async Task Body_failure_after_probe_scheduler_enters_stops_probe_and_disposes_client()
+    {
+        var client = CannedAgentClient.FromFixtures();
+        var entered = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var released = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var cancelled = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var driver = new MTConnectDriver(Opts(), "mt1", _ => client,
+            probeScheduler: async (_, ct) =>
+            {
+                entered.TrySetResult();
+                try { await released.Task.WaitAsync(ct); }
+                catch (OperationCanceledException) when (ct.IsCancellationRequested)
+                {
+                    cancelled.TrySetResult();
+                    throw;
+                }
+            });
+        Task? probe = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        try
+        {
+            var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+            {
+                await driver.InitializeAsync("{}", CancellationToken.None);
+                await entered.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+                probe = driver.ProbeLoopTask;
+                _ = probe.ShouldNotBeNull();
+                probe!.IsCompleted.ShouldBeFalse();
+                client.IsDisposed.ShouldBeFalse();
+                throw sentinel;
+            }, () => driver.ShutdownAsync(CancellationToken.None),
+                failure => output.WriteLine($"MTConnect probe fixture cleanup failed: {failure}")));
+            actual.ShouldBeSameAs(sentinel);
+            await cancelled.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+            probe!.IsCompleted.ShouldBeTrue();
+            client.DisposeCount.ShouldBe(1);
+        }
+        finally { released.TrySetResult(); }
+    }
+
+    [Fact]
+    public async Task Initialization_failure_disposes_the_client_inside_fixture_boundary()
+    {
+        var client = CannedAgentClient.FromFixtures();
+        var failure = new HttpRequestException("current unavailable");
+        client.CurrentFailure = failure;
+        var driver = new MTConnectDriver(Opts(), "mt1", _ => client);
+        var actual = await Should.ThrowAsync<HttpRequestException>(() => FixtureCleanup.RunAsync(
+            () => driver.InitializeAsync("{}", CancellationToken.None),
+            () => driver.ShutdownAsync(CancellationToken.None),
+            secondary => output.WriteLine($"MTConnect init fixture cleanup failed: {secondary}")));
+        actual.ShouldBeSameAs(failure);
+        client.DisposeCount.ShouldBe(1);
     }
 
     [Fact]
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests.csproj b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests.csproj
index 866f7a9e..6b067f74 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests.csproj
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests.csproj
@@ -39,4 +39,7 @@
         </Content>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusLifecycleHygieneTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusLifecycleHygieneTests.cs
index 316de319..35417060 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusLifecycleHygieneTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusLifecycleHygieneTests.cs
@@ -1,6 +1,7 @@
 using System.Collections.Concurrent;
 using System.Reflection;
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Driver.Modbus;
@@ -14,7 +15,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests;
 ///     unit test alongside them per Driver.Modbus-012.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class ModbusLifecycleHygieneTests
+public sealed class ModbusLifecycleHygieneTests(ITestOutputHelper output)
 {
     private sealed class FakeTransport : IModbusTransport
     {
@@ -528,7 +529,7 @@ public sealed class ModbusLifecycleHygieneTests
 
     /// <summary>Verifies that DecodeBitArray rejects an empty bitmap with InvalidDataException.</summary>
     [Fact]
-    public void DecodeBitArray_rejects_an_empty_bitmap_with_InvalidDataException()
+    public async Task DecodeBitArray_rejects_an_empty_bitmap_with_InvalidDataException()
     {
         var decode = typeof(ModbusDriver).GetMethod(
             "DecodeBitArray", BindingFlags.NonPublic | BindingFlags.Static)!;
@@ -542,11 +543,49 @@ public sealed class ModbusLifecycleHygieneTests
             RawTags = ModbusRawTags.Entries([new ModbusTagDefinition("Coil", ModbusRegion.Coils, 0, ModbusDataType.Bool)]),
         };
         var drv = new ModbusDriver(opts, "modbus-1", _ => fake);
-        drv.InitializeAsync("{}", CancellationToken.None).GetAwaiter().GetResult();
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var r = drv.ReadAsync(["Coil"], CancellationToken.None).GetAwaiter().GetResult();
-        // The empty-bitmap guard surfaces via the BadCommunicationError catch-all.
-        r[0].StatusCode.ShouldBe(0x80050000u);
+            var r = await drv.ReadAsync(["Coil"], CancellationToken.None);
+            // The empty-bitmap guard surfaces via the BadCommunicationError catch-all.
+            r[0].StatusCode.ShouldBe(0x80050000u);
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"Modbus empty bitmap cleanup failed: {failure}"));
+    }
+
+    [Fact]
+    public async Task Body_failure_after_probe_request_cancels_it_and_disposes_transport()
+    {
+        var fake = new EmptyBitTransport();
+        var opts = new ModbusDriverOptions
+        {
+            Host = "fake",
+            RawTags = ModbusRawTags.Entries([new ModbusTagDefinition("Coil", ModbusRegion.Coils, 0, ModbusDataType.Bool)]),
+        };
+        var drv = new ModbusDriver(opts, "modbus-1", _ => fake);
+        var sentinel = new InvalidOperationException("body sentinel");
+        try
+        {
+            var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                var result = await drv.ReadAsync(["Coil"], CancellationToken.None);
+                result[0].StatusCode.ShouldBe(0x80050000u);
+                fake.CoilRequestCount.ShouldBe(1);
+                await fake.ProbeEntered.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+                fake.ProbeToken.IsCancellationRequested.ShouldBeFalse();
+                fake.DisposeCount.ShouldBe(0);
+                throw sentinel;
+            }, () => drv.ShutdownAsync(CancellationToken.None),
+                failure => output.WriteLine($"Modbus probe fixture cleanup failed: {failure}")));
+            actual.ShouldBeSameAs(sentinel);
+            fake.ProbeToken.IsCancellationRequested.ShouldBeTrue();
+            await fake.ProbeCancelled.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+            await fake.ProbeRequestCompleted.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+            fake.DisposeCount.ShouldBe(1);
+        }
+        finally { fake.ReleaseProbe.TrySetResult(); }
     }
 
     /// <summary>
@@ -556,6 +595,14 @@ public sealed class ModbusLifecycleHygieneTests
     /// </summary>
     private sealed class EmptyBitTransport : IModbusTransport
     {
+        public TaskCompletionSource ProbeEntered { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        public TaskCompletionSource ProbeCancelled { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        public TaskCompletionSource ProbeRequestCompleted { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        public TaskCompletionSource ReleaseProbe { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        public CancellationToken ProbeToken { get; private set; }
+        public int DisposeCount { get; private set; }
+        public int CoilRequestCount { get; private set; }
+
         /// <summary>Returns a completed task without performing any connection.</summary>
         /// <param name="ct">The cancellation token for the operation.</param>
         public Task ConnectAsync(CancellationToken ct) => Task.CompletedTask;
@@ -563,10 +610,29 @@ public sealed class ModbusLifecycleHygieneTests
         /// <param name="unitId">The Modbus unit ID.</param>
         /// <param name="pdu">The protocol data unit being sent.</param>
         /// <param name="ct">The cancellation token for the operation.</param>
-        public Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
-            => Task.FromResult(new byte[] { pdu[0], 0 });
-        /// <summary>Completes the disposal without doing any work.</summary>
-        public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+        public async Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
+        {
+            if (pdu[0] == 0x03)
+            {
+                ProbeToken = ct;
+                ProbeEntered.TrySetResult();
+                try { await ReleaseProbe.Task.WaitAsync(ct); }
+                catch (OperationCanceledException) when (ct.IsCancellationRequested)
+                {
+                    ProbeCancelled.TrySetResult();
+                    throw;
+                }
+                finally { ProbeRequestCompleted.TrySetResult(); }
+            }
+            if (pdu[0] == 0x01) CoilRequestCount++;
+            return new byte[] { pdu[0], 0 };
+        }
+        /// <summary>Records transport disposal.</summary>
+        public ValueTask DisposeAsync()
+        {
+            DisposeCount++;
+            return ValueTask.CompletedTask;
+        }
     }
 
     // -------------------- Finding -003 (volatile _health) --------------------
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests.csproj b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests.csproj
index 980a367b..0dfbd27b 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests.csproj
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests.csproj
@@ -29,4 +29,7 @@
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Modbus\ZB.MOM.WW.OtOpcUa.Driver.Modbus.csproj"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATReinitializeReleasesStateTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATReinitializeReleasesStateTests.cs
index 8ef5f9eb..529f1d12 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATReinitializeReleasesStateTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATReinitializeReleasesStateTests.cs
@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
@@ -8,7 +9,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
 ///     orphaned the previous state's probe loop + client. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class TwinCATReinitializeReleasesStateTests
+public sealed class TwinCATReinitializeReleasesStateTests(ITestOutputHelper output)
 {
     /// <summary>Initialize twice: the first state's probe loop has finished and its client is disposed.</summary>
     [Fact]
@@ -21,28 +22,88 @@ public sealed class TwinCATReinitializeReleasesStateTests
             Devices = [new TwinCATDeviceOptions(host)],
             Probe = new TwinCATProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), Timeout = TimeSpan.FromSeconds(1) },
         }, "drv-reinit", factory);
-        await drv.InitializeAsync("{}", CancellationToken.None);
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var first = drv.GetDeviceState(host)!;
-        // Positive control: the first probe loop is running and holds a connected client.
+            var first = drv.GetDeviceState(host)!;
+            // Positive control: the first probe loop is running and holds a connected client.
+            var deadline = DateTime.UtcNow.AddSeconds(5);
+            while (!(factory.Clients.Count > 0 && factory.Clients[0].IsConnected))
+            {
+                if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never connected");
+                await Task.Delay(10);
+            }
+            var firstClient = factory.Clients[0];
+            var firstLoop = first.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+
+            await drv.InitializeAsync("{}", CancellationToken.None);
+
+            firstLoop.IsCompleted.ShouldBeTrue(); // joined
+            firstClient.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            firstClient.IsConnected.ShouldBeFalse();
+            drv.GetDeviceState(host).ShouldNotBeSameAs(first);
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"TwinCAT SecondInitialize cleanup failed: {failure}"));
+    }
+
+    /// <summary>Failure after a live first or replacement state must release both owned resources.</summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task Body_failure_releases_live_probe_resources(bool afterReplacement)
+    {
+        const string host = "ads://5.23.91.23.1.1:851";
+        var factory = new FakeTwinCATClientFactory();
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions(host)],
+            Probe = new TwinCATProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), Timeout = TimeSpan.FromSeconds(1) },
+        }, "drv-reinit", factory);
+        Task? firstLoop = null, secondLoop = null;
+        FakeTwinCATClient? firstClient = null, secondClient = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
+            await WaitUntilAsync(() => factory.Clients.Count > 0 && factory.Clients[0].IsConnected);
+            firstClient = factory.Clients[0];
+            firstLoop = drv.GetDeviceState(host)!.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            if (afterReplacement)
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                await WaitUntilAsync(() => factory.Clients.Count > 1 && factory.Clients[1].IsConnected);
+                secondClient = factory.Clients[1];
+                secondLoop = drv.GetDeviceState(host)!.ProbeTask;
+                _ = secondLoop.ShouldNotBeNull();
+                secondLoop!.IsCompleted.ShouldBeFalse();
+            }
+            throw sentinel;
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"TwinCAT failure fixture cleanup failed: {failure}")));
+        actual.ShouldBeSameAs(sentinel);
+        firstLoop!.IsCompleted.ShouldBeTrue();
+        firstClient!.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+        firstClient.IsConnected.ShouldBeFalse();
+        if (afterReplacement)
+        {
+            secondLoop!.IsCompleted.ShouldBeTrue();
+            secondClient!.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            secondClient.IsConnected.ShouldBeFalse();
+        }
+    }
+
+    private static async Task WaitUntilAsync(Func<bool> condition)
+    {
         var deadline = DateTime.UtcNow.AddSeconds(5);
-        while (!(factory.Clients.Count > 0 && factory.Clients[0].IsConnected))
+        while (!condition())
         {
             if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never connected");
             await Task.Delay(10);
         }
-        var firstClient = factory.Clients[0];
-        var firstLoop = first.ProbeTask;
-        firstLoop.ShouldNotBeNull();
-        firstLoop!.IsCompleted.ShouldBeFalse();
-
-        await drv.InitializeAsync("{}", CancellationToken.None);
-
-        firstLoop.IsCompleted.ShouldBeTrue(); // joined
-        firstClient.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
-        firstClient.IsConnected.ShouldBeFalse();
-        drv.GetDeviceState(host).ShouldNotBeSameAs(first);
-
-        await drv.ShutdownAsync(CancellationToken.None);
     }
 }
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests.csproj b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests.csproj
index fd7dacec..8b1dbba6 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests.csproj
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests.csproj
@@ -29,4 +29,7 @@
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.csproj"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>
diff --git a/tests/TestSupport/FixtureCleanup.cs b/tests/TestSupport/FixtureCleanup.cs
new file mode 100644
index 00000000..4cdaac85
--- /dev/null
+++ b/tests/TestSupport/FixtureCleanup.cs
@@ -0,0 +1,32 @@
+namespace ZB.MOM.WW.OtOpcUa.Tests;
+
+internal static class FixtureCleanup
+{
+    internal const string SecondaryExceptionKey = "FixtureCleanup.SecondaryException";
+
+    internal static async Task RunAsync(Func<Task> body, Func<Task> cleanup, Action<Exception> report)
+    {
+        Exception? primary = null;
+        try
+        {
+            await body();
+        }
+        catch (Exception failure)
+        {
+            primary = failure;
+            throw;
+        }
+        finally
+        {
+            try
+            {
+                await cleanup();
+            }
+            catch (Exception secondary) when (primary is not null)
+            {
+                try { primary.Data[SecondaryExceptionKey] = secondary; } catch { }
+                try { report(secondary); } catch { }
+            }
+        }
+    }
+}