Implement worker heartbeat watchdog

Issue #19: gateway end-to-end smoke with fake worker

docs/GatewayTesting.md

@@ -0,0 +1,61 @@
+# Gateway Testing
+
+Gateway tests run without installed MXAccess by using fake workers, fake
+transports, and in-process gRPC service fakes. Live MXAccess verification belongs
+in opt-in integration tests because it depends on installed COM components and
+provider state.
+
+## Fake Worker Harness
+
+`FakeWorkerHarness` in `src/MxGateway.Tests/Gateway/Workers/Fakes/` provides an
+in-process worker side for named-pipe IPC tests. It uses the same
+`WorkerFrameReader`, `WorkerFrameWriter`, and `WorkerEnvelope` contract as the
+gateway so tests exercise real frame validation and worker-client state changes.
+
+Use the harness when a gateway or session test needs worker behavior without
+starting `MxGateway.Worker.exe` or loading MXAccess COM. The harness scripts:
+
+- `WorkerHello` and `WorkerReady` startup,
+- command replies with matching correlation ids,
+- ordered `WorkerEvent` frames,
+- `WorkerHeartbeat` frames,
+- `WorkerFault` frames,
+- shutdown acknowledgements,
+- malformed protobuf payloads and oversized frame headers,
+- slow or hung workers by withholding a reply.
+
+Session-level tests can connect the harness to the pipe created by
+`SessionWorkerClientFactory` with `ConnectToGatewayPipeAsync`. Lower-level
+`WorkerClient` tests can use `CreateConnectedPairAsync` to create both pipe ends
+inside the test.
+
+`GatewayEndToEndFakeWorkerSmokeTests` composes the real gRPC service,
+`SessionManager`, `SessionWorkerClientFactory`, `WorkerClient`, and
+`EventStreamService` with a scripted fake worker launcher. The smoke test covers
+`OpenSession`, `Register`, `AddItem`, `Advise`, one streamed `OnDataChange`
+event, and `CloseSession` without loading MXAccess COM.
+
+## Focused Commands
+
+Run the fake worker tests after changing gateway worker IPC, session startup, or
+event streaming behavior:
+
+```bash
+dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter FullyQualifiedName~FakeWorkerHarnessTests
+dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter FullyQualifiedName~SessionWorkerClientFactoryFakeWorkerTests
+dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter FullyQualifiedName~GatewayEndToEndFakeWorkerSmokeTests
+dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter FullyQualifiedName~WorkerClientTests
+dotnet test src/MxGateway.Worker.Tests/MxGateway.Worker.Tests.csproj -p:Platform=x86 --filter FullyQualifiedName~WorkerPipeSessionTests
+```
+
+Run the gateway test project after shared gateway test infrastructure changes:
+
+```bash
+dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj
+```
+
+## Related Documentation
+
+- [Gateway Process Design](./gateway-process-design.md)
+- [Worker Frame Protocol](./WorkerFrameProtocol.md)
+- [MXAccess Worker Instance Detailed Design](./mxaccess-worker-instance-design.md)

docs/gateway-process-design.md

@@ -891,6 +891,11 @@ behavior unless an explicit non-parity backend is designed.
 Gateway tests should be able to run without installed MXAccess by using fake
 workers and fake transports.
 
+Use `FakeWorkerHarness` for tests that need real gateway-to-worker framing,
+handshake, command, event, fault, or malformed-protocol behavior without loading
+MXAccess COM. See [Gateway Testing](./GatewayTesting.md) for the harness scope
+and focused test commands.
+
 Focused tests:
 
 - session state transitions,

docs/implementation-plan-mxaccess-worker.md

@@ -218,6 +218,8 @@ Live tests:
 
 Labels: `area:worker`, `type:feature`, `priority:p0`
 
+Status: implemented.
+
 Deliverables:
 
 - `AddItem`,

docs/mxaccess-worker-instance-design.md

@@ -432,6 +432,25 @@ HRESULT and converts the reply to `ProtocolStatusCode.MxaccessFailure`.
 `MxAccessStaSession.GetRegisteredServerHandlesAsync` returns an STA-read
 snapshot of tracked server handles for diagnostics and future cleanup logic.
 
+`MxAccessCommandExecutor` also implements the item lifecycle commands:
+
+- `AddItem` calls `LMXProxyServerClass.AddItem` with the requested server
+  handle and item definition. It preserves the returned item handle in both
+  `ReturnValue` and `AddItemReply.ItemHandle`.
+- `AddItem2` calls `LMXProxyServerClass.AddItem2` with the requested server
+  handle, item definition, and context string. The context string is passed to
+  MXAccess exactly as received.
+- `RemoveItem` calls `LMXProxyServerClass.RemoveItem` with the requested server
+  handle and item handle. The reply has no method-specific payload because the
+  public MXAccess method returns `void`.
+
+The worker records item handles only after `AddItem` or `AddItem2` returns
+normally, and removes item handles only after `RemoveItem` returns normally.
+The registry does not prevalidate server or item handles, so invalid and
+cross-server handle behavior remains owned by MXAccess. COM exceptions continue
+through `StaCommandDispatcher`, which preserves the HRESULT and leaves
+diagnostic registry state unchanged for failed cleanup calls.
+
 ## Handle Registry
 
 The worker should track MXAccess state for diagnostics and cleanup, while still
@@ -454,6 +473,8 @@ Rules:
 - Do not rewrite handles returned by MXAccess.
 - Record server handles only after `Register` succeeds.
 - Remove server handles only after `Unregister` succeeds.
+- Record item handles only after `AddItem` or `AddItem2` succeeds.
+- Remove item handles only after `RemoveItem` succeeds.
 - Preserve invalid-handle behavior from MXAccess.
 - Preserve cross-server handle behavior from MXAccess.
 - Use registry state for cleanup and diagnostics, not semantic correction.
@@ -555,13 +576,19 @@ Do not drop or coalesce events in v1.
 
 ## Heartbeat And Watchdog
 
-The worker heartbeat should prove that:
+`WorkerPipeSession` starts the heartbeat loop after the gateway validates
+`WorkerHello` and receives `WorkerReady`. Heartbeats continue until
+`WorkerShutdown`, cancellation, or a pipe/protocol failure stops the session.
+The loop uses `WorkerPipeSessionOptions.HeartbeatInterval`; the default matches
+the gateway worker heartbeat interval.
+
+The worker heartbeat proves that:
 
 - pipe writer is alive,
 - worker host is alive,
 - STA has recently pumped or completed work.
 
-Heartbeat payload should include:
+Heartbeat payload includes:
 
 - worker process id,
 - session id,
@@ -572,13 +599,19 @@ Heartbeat payload should include:
 - event sequence,
 - current command correlation id if any.
 
-The STA watchdog should warn when:
+`MxAccessStaSession.CaptureHeartbeat()` reads `StaRuntime.LastActivityUtc` and
+`StaCommandDispatcher` queue state without touching the raw MXAccess COM object
+outside the STA. Event queue depth and event sequence are reported as zero until
+the event queue implementation owns those counters.
 
-- one command exceeds its expected duration,
+The STA watchdog currently emits a `WorkerFault` with
-- the STA has not pumped messages within the heartbeat grace period,
+`WorkerFaultCategory.StaHung` when `LastStaActivityUtc` is older than
-- event queue depth remains high.
+`WorkerPipeSessionOptions.HeartbeatGrace`. The fault includes the current
-
+command correlation id when a command is active. Command duration and high event
-The worker can report the problem, but the gateway owns the final kill decision.
+queue depth remain observable through heartbeat fields until dedicated
+thresholds own those warnings. The worker reports stale STA activity, but the
+gateway owns the final kill decision through its existing heartbeat and worker
+lifecycle policy.
 
 ## Shutdown
 
@@ -697,6 +730,10 @@ Live MXAccess tests:
 
 Live tests should be opt-in and clearly marked because they depend on installed
 MXAccess COM and provider state.
+The worker test suite uses `MXGATEWAY_RUN_LIVE_MXACCESS_TESTS=1` for these
+tests. `AddItem` uses `TestChildObject.TestInt` by default and accepts an
+override through `MXGATEWAY_LIVE_MXACCESS_ITEM`; `AddItem2` uses the captured
+parity fixture shape `AddItem2("TestInt", "TestChildObject")`.
 
 ## Initial Implementation Slice
 

src/MxGateway.Tests/Gateway/GatewayEndToEndFakeWorkerSmokeTests.cs

@@ -0,0 +1,439 @@
+using System.Collections.Concurrent;
+using Google.Protobuf.WellKnownTypes;
+using Grpc.Core;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using MxGateway.Contracts;
+using MxGateway.Contracts.Proto;
+using MxGateway.Server.Configuration;
+using MxGateway.Server.Grpc;
+using MxGateway.Server.Metrics;
+using MxGateway.Server.Security.Authorization;
+using MxGateway.Server.Sessions;
+using MxGateway.Server.Workers;
+using MxGateway.Tests.Gateway.Workers.Fakes;
+
+namespace MxGateway.Tests.Gateway;
+
+public sealed class GatewayEndToEndFakeWorkerSmokeTests
+{
+    private static readonly TimeSpan TestTimeout = TimeSpan.FromSeconds(5);
+    private const int ServerHandle = 1001;
+    private const int ItemHandle = 2002;
+
+    [Fact]
+    public async Task GatewayService_WithFakeWorker_CompletesSessionCommandEventAndClosePath()
+    {
+        ScriptedFakeWorkerProcessLauncher launcher = new();
+        await using GatewayServiceFixture fixture = new(launcher);
+
+        OpenSessionReply openReply = await fixture.Service.OpenSession(
+            new OpenSessionRequest
+            {
+                ClientSessionName = "fake-worker-e2e",
+                ClientCorrelationId = "open-correlation",
+                CommandTimeout = Duration.FromTimeSpan(TestTimeout),
+            },
+            new TestServerCallContext());
+
+        RecordingServerStreamWriter<MxEvent> eventWriter = new();
+        Task streamTask = fixture.Service.StreamEvents(
+            new StreamEventsRequest { SessionId = openReply.SessionId },
+            eventWriter,
+            new TestServerCallContext());
+
+        MxCommandReply registerReply = await fixture.Service.Invoke(
+            CreateRegisterRequest(openReply.SessionId),
+            new TestServerCallContext());
+        MxCommandReply addItemReply = await fixture.Service.Invoke(
+            CreateAddItemRequest(openReply.SessionId, registerReply.Register.ServerHandle),
+            new TestServerCallContext());
+        MxCommandReply adviseReply = await fixture.Service.Invoke(
+            CreateAdviseRequest(openReply.SessionId, registerReply.Register.ServerHandle, addItemReply.AddItem.ItemHandle),
+            new TestServerCallContext());
+
+        MxEvent dataChange = await eventWriter.WaitForFirstMessageAsync(TestTimeout);
+
+        CloseSessionReply closeReply = await fixture.Service.CloseSession(
+            new CloseSessionRequest
+            {
+                SessionId = openReply.SessionId,
+                ClientCorrelationId = "close-correlation",
+            },
+            new TestServerCallContext());
+
+        await streamTask.WaitAsync(TestTimeout);
+        await launcher.WorkerTask.WaitAsync(TestTimeout);
+
+        Assert.Equal(ProtocolStatusCode.Ok, openReply.ProtocolStatus.Code);
+        Assert.Equal(GatewayContractInfo.DefaultBackendName, openReply.BackendName);
+        Assert.Equal(ScriptedFakeWorkerProcessLauncher.ProcessId, openReply.WorkerProcessId);
+        Assert.Equal(ProtocolStatusCode.Ok, registerReply.ProtocolStatus.Code);
+        Assert.Equal(ServerHandle, registerReply.Register.ServerHandle);
+        Assert.Equal(ProtocolStatusCode.Ok, addItemReply.ProtocolStatus.Code);
+        Assert.Equal(ItemHandle, addItemReply.AddItem.ItemHandle);
+        Assert.Equal(ProtocolStatusCode.Ok, adviseReply.ProtocolStatus.Code);
+        Assert.Equal(MxEventFamily.OnDataChange, dataChange.Family);
+        Assert.Equal(openReply.SessionId, dataChange.SessionId);
+        Assert.Equal(ServerHandle, dataChange.ServerHandle);
+        Assert.Equal(ItemHandle, dataChange.ItemHandle);
+        Assert.Equal("scripted-value", dataChange.Value.StringValue);
+        Assert.Equal(ProtocolStatusCode.Ok, closeReply.ProtocolStatus.Code);
+        Assert.Equal(SessionState.Closed, closeReply.FinalState);
+        Assert.True(launcher.Process.HasExited);
+        Assert.Equal(
+            [MxCommandKind.Register, MxCommandKind.AddItem, MxCommandKind.Advise],
+            launcher.CommandKinds);
+    }
+
+    private static MxCommandRequest CreateRegisterRequest(string sessionId)
+    {
+        return new MxCommandRequest
+        {
+            SessionId = sessionId,
+            ClientCorrelationId = "register-correlation",
+            Command = new MxCommand
+            {
+                Kind = MxCommandKind.Register,
+                Register = new RegisterCommand { ClientName = "fake-worker-e2e-client" },
+            },
+        };
+    }
+
+    private static MxCommandRequest CreateAddItemRequest(
+        string sessionId,
+        int serverHandle)
+    {
+        return new MxCommandRequest
+        {
+            SessionId = sessionId,
+            ClientCorrelationId = "add-item-correlation",
+            Command = new MxCommand
+            {
+                Kind = MxCommandKind.AddItem,
+                AddItem = new AddItemCommand
+                {
+                    ServerHandle = serverHandle,
+                    ItemDefinition = "Galaxy.Tag.Value",
+                },
+            },
+        };
+    }
+
+    private static MxCommandRequest CreateAdviseRequest(
+        string sessionId,
+        int serverHandle,
+        int itemHandle)
+    {
+        return new MxCommandRequest
+        {
+            SessionId = sessionId,
+            ClientCorrelationId = "advise-correlation",
+            Command = new MxCommand
+            {
+                Kind = MxCommandKind.Advise,
+                Advise = new AdviseCommand
+                {
+                    ServerHandle = serverHandle,
+                    ItemHandle = itemHandle,
+                },
+            },
+        };
+    }
+
+    private sealed class GatewayServiceFixture : IAsyncDisposable
+    {
+        private readonly GatewayMetrics _metrics = new();
+        private readonly SessionRegistry _registry = new();
+
+        public GatewayServiceFixture(IWorkerProcessLauncher launcher)
+        {
+            IOptions<GatewayOptions> options = Options.Create(CreateOptions());
+            SessionWorkerClientFactory workerClientFactory = new(
+                launcher,
+                options,
+                _metrics,
+                NullLoggerFactory.Instance);
+            SessionManager sessionManager = new(
+                _registry,
+                workerClientFactory,
+                options,
+                _metrics,
+                logger: NullLogger<SessionManager>.Instance);
+            MxAccessGrpcMapper mapper = new();
+            EventStreamService eventStreamService = new(
+                sessionManager,
+                options,
+                mapper,
+                _metrics,
+                NullLogger<EventStreamService>.Instance);
+
+            Service = new MxAccessGatewayService(
+                sessionManager,
+                new GatewayRequestIdentityAccessor(),
+                new MxAccessGrpcRequestValidator(),
+                mapper,
+                eventStreamService,
+                NullLogger<MxAccessGatewayService>.Instance);
+        }
+
+        public MxAccessGatewayService Service { get; }
+
+        public async ValueTask DisposeAsync()
+        {
+            foreach (GatewaySession session in _registry.Snapshot())
+            {
+                await session.DisposeAsync();
+            }
+
+            _metrics.Dispose();
+        }
+
+        private static GatewayOptions CreateOptions()
+        {
+            return new GatewayOptions
+            {
+                Worker = new WorkerOptions
+                {
+                    StartupTimeoutSeconds = 5,
+                    ShutdownTimeoutSeconds = 5,
+                    HeartbeatIntervalSeconds = 30,
+                    HeartbeatGraceSeconds = 30,
+                    MaxMessageBytes = WorkerFrameProtocolOptions.DefaultMaxMessageBytes,
+                },
+                Sessions = new SessionOptions
+                {
+                    DefaultCommandTimeoutSeconds = 5,
+                    MaxSessions = 4,
+                },
+                Events = new EventOptions
+                {
+                    QueueCapacity = 16,
+                },
+            };
+        }
+    }
+
+    private sealed class ScriptedFakeWorkerProcessLauncher : IWorkerProcessLauncher
+    {
+        public const int ProcessId = 4680;
+        private readonly ConcurrentQueue<MxCommandKind> _commandKinds = new();
+
+        public FakeWorkerProcess Process { get; } = new(ProcessId);
+
+        public IReadOnlyCollection<MxCommandKind> CommandKinds => _commandKinds.ToArray();
+
+        public Task WorkerTask { get; private set; } = Task.CompletedTask;
+
+        public Task<WorkerProcessHandle> LaunchAsync(
+            WorkerProcessLaunchRequest request,
+            CancellationToken cancellationToken = default)
+        {
+            WorkerTask = RunWorkerAsync(request, cancellationToken);
+
+            return Task.FromResult(new WorkerProcessHandle(
+                Process,
+                new WorkerProcessCommandLine("fake-worker.exe", []),
+                DateTimeOffset.UtcNow));
+        }
+
+        private async Task RunWorkerAsync(
+            WorkerProcessLaunchRequest request,
+            CancellationToken cancellationToken)
+        {
+            await using FakeWorkerHarness harness = await FakeWorkerHarness.ConnectToGatewayPipeAsync(
+                request.SessionId,
+                request.Nonce,
+                request.PipeName,
+                request.ProtocolVersion,
+                cancellationToken: cancellationToken).ConfigureAwait(false);
+            await harness.CompleteStartupAsync(ProcessId, cancellationToken: cancellationToken).ConfigureAwait(false);
+
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                WorkerEnvelope envelope = await harness.ReadGatewayEnvelopeAsync(cancellationToken).ConfigureAwait(false);
+                if (envelope.BodyCase == WorkerEnvelope.BodyOneofCase.WorkerCommand)
+                {
+                    await ReplyToCommandAsync(harness, envelope, cancellationToken).ConfigureAwait(false);
+                    continue;
+                }
+
+                if (envelope.BodyCase == WorkerEnvelope.BodyOneofCase.WorkerShutdown)
+                {
+                    await harness.SendShutdownAckAsync(cancellationToken: cancellationToken).ConfigureAwait(false);
+                    Process.MarkExited(0);
+                    return;
+                }
+
+                throw new InvalidOperationException($"Unexpected gateway envelope {envelope.BodyCase}.");
+            }
+        }
+
+        private async Task ReplyToCommandAsync(
+            FakeWorkerHarness harness,
+            WorkerEnvelope commandEnvelope,
+            CancellationToken cancellationToken)
+        {
+            MxCommand command = commandEnvelope.WorkerCommand.Command;
+            _commandKinds.Enqueue(command.Kind);
+
+            await harness.ReplyToCommandAsync(
+                commandEnvelope,
+                configureReply: reply => ConfigureReply(reply, command.Kind),
+                cancellationToken: cancellationToken).ConfigureAwait(false);
+
+            if (command.Kind == MxCommandKind.Advise)
+            {
+                await harness.EmitEventAsync(
+                    MxEventFamily.OnDataChange,
+                    cancellationToken,
+                    mxEvent =>
+                    {
+                        mxEvent.ServerHandle = command.Advise.ServerHandle;
+                        mxEvent.ItemHandle = command.Advise.ItemHandle;
+                        mxEvent.Quality = 192;
+                        mxEvent.Value = new MxValue
+                        {
+                            DataType = MxDataType.String,
+                            StringValue = "scripted-value",
+                        };
+                        mxEvent.OnDataChange = new OnDataChangeEvent();
+                    }).ConfigureAwait(false);
+            }
+        }
+
+        private static void ConfigureReply(
+            MxCommandReply reply,
+            MxCommandKind kind)
+        {
+            switch (kind)
+            {
+                case MxCommandKind.Register:
+                    reply.Register = new RegisterReply { ServerHandle = ServerHandle };
+                    break;
+                case MxCommandKind.AddItem:
+                    reply.AddItem = new AddItemReply { ItemHandle = ItemHandle };
+                    break;
+            }
+        }
+    }
+
+    private sealed class FakeWorkerProcess(int processId) : IWorkerProcess
+    {
+        public int Id { get; } = processId;
+
+        public bool HasExited { get; private set; }
+
+        public int? ExitCode { get; private set; }
+
+        public ValueTask WaitForExitAsync(CancellationToken cancellationToken)
+        {
+            HasExited = true;
+            ExitCode ??= 0;
+            return ValueTask.CompletedTask;
+        }
+
+        public void Kill(bool entireProcessTree)
+        {
+            MarkExited(-1);
+        }
+
+        public void Dispose()
+        {
+        }
+
+        public void MarkExited(int exitCode)
+        {
+            HasExited = true;
+            ExitCode = exitCode;
+        }
+    }
+
+    private sealed class RecordingServerStreamWriter<T> : IServerStreamWriter<T>
+    {
+        private readonly object _syncRoot = new();
+        private readonly TaskCompletionSource<T> _firstMessage = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        private readonly List<T> _messages = [];
+
+        public IReadOnlyList<T> Messages
+        {
+            get
+            {
+                lock (_syncRoot)
+                {
+                    return _messages.ToArray();
+                }
+            }
+        }
+
+        public WriteOptions? WriteOptions { get; set; }
+
+        public Task WriteAsync(T message)
+        {
+            lock (_syncRoot)
+            {
+                _messages.Add(message);
+            }
+
+            _firstMessage.TrySetResult(message);
+            return Task.CompletedTask;
+        }
+
+        public async Task<T> WaitForFirstMessageAsync(TimeSpan timeout)
+        {
+            return await _firstMessage.Task.WaitAsync(timeout).ConfigureAwait(false);
+        }
+    }
+
+    private sealed class TestServerCallContext(CancellationToken cancellationToken = default) : ServerCallContext
+    {
+        private readonly Metadata _requestHeaders = [];
+        private readonly Metadata _responseTrailers = [];
+        private readonly Dictionary<object, object> _userState = [];
+        private Status _status;
+        private WriteOptions? _writeOptions;
+
+        protected override string MethodCore => "/mxaccess_gateway.v1.MxAccessGateway/Test";
+
+        protected override string HostCore => "localhost";
+
+        protected override string PeerCore => "ipv4:127.0.0.1:5000";
+
+        protected override DateTime DeadlineCore => DateTime.UtcNow.AddMinutes(1);
+
+        protected override Metadata RequestHeadersCore => _requestHeaders;
+
+        protected override CancellationToken CancellationTokenCore => cancellationToken;
+
+        protected override Metadata ResponseTrailersCore => _responseTrailers;
+
+        protected override Status StatusCore
+        {
+            get => _status;
+            set => _status = value;
+        }
+
+        protected override WriteOptions? WriteOptionsCore
+        {
+            get => _writeOptions;
+            set => _writeOptions = value;
+        }
+
+        protected override AuthContext AuthContextCore { get; } = new(
+            string.Empty,
+            new Dictionary<string, List<AuthProperty>>(StringComparer.Ordinal));
+
+        protected override IDictionary<object, object> UserStateCore => _userState;
+
+        protected override Task WriteResponseHeadersAsyncCore(Metadata responseHeaders)
+        {
+            return Task.CompletedTask;
+        }
+
+        protected override ContextPropagationToken CreatePropagationTokenCore(
+            ContextPropagationOptions? options)
+        {
+            throw new NotSupportedException();
+        }
+    }
+}

src/MxGateway.Tests/Gateway/Sessions/SessionWorkerClientFactoryFakeWorkerTests.cs

@@ -0,0 +1,216 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using MxGateway.Contracts;
+using MxGateway.Contracts.Proto;
+using MxGateway.Server.Configuration;
+using MxGateway.Server.Metrics;
+using MxGateway.Server.Sessions;
+using MxGateway.Server.Workers;
+using MxGateway.Tests.Gateway.Workers.Fakes;
+
+namespace MxGateway.Tests.Gateway.Sessions;
+
+public sealed class SessionWorkerClientFactoryFakeWorkerTests
+{
+    private static readonly TimeSpan TestTimeout = TimeSpan.FromSeconds(5);
+
+    [Fact]
+    public async Task CreateAsync_WithScriptedFakeWorker_ReturnsReadyClient()
+    {
+        ScriptedFakeWorkerProcessLauncher launcher = new();
+        using GatewayMetrics metrics = new();
+        SessionWorkerClientFactory factory = new(
+            launcher,
+            Options.Create(CreateOptions()),
+            metrics,
+            NullLoggerFactory.Instance);
+        GatewaySession session = CreateSession();
+
+        await using IWorkerClient workerClient = await factory.CreateAsync(
+            session,
+            CancellationToken.None);
+
+        Assert.Equal(WorkerClientState.Ready, workerClient.State);
+        Assert.Equal(ScriptedFakeWorkerProcessLauncher.ProcessId, workerClient.ProcessId);
+        Assert.NotNull(launcher.Harness);
+
+        Task<WorkerCommandReply> invokeTask = workerClient.InvokeAsync(
+            CreateCommand(MxCommandKind.Ping),
+            TestTimeout,
+            CancellationToken.None);
+        WorkerEnvelope commandEnvelope = await launcher.Harness.ReadCommandAsync();
+        await launcher.Harness.ReplyToCommandAsync(commandEnvelope);
+        WorkerCommandReply reply = await invokeTask.WaitAsync(TestTimeout);
+
+        Assert.Equal(MxCommandKind.Ping, reply.Reply.Kind);
+        Assert.Equal(ProtocolStatusCode.Ok, reply.Reply.ProtocolStatus.Code);
+    }
+
+    [Fact]
+    public async Task CreateAsync_WhenFakeWorkerStartupFails_ThrowsWorkerClientException()
+    {
+        FailingStartupWorkerProcessLauncher launcher = new();
+        using GatewayMetrics metrics = new();
+        SessionWorkerClientFactory factory = new(
+            launcher,
+            Options.Create(CreateOptions()),
+            metrics,
+            NullLoggerFactory.Instance);
+        GatewaySession session = CreateSession();
+
+        WorkerClientException exception = await Assert.ThrowsAsync<WorkerClientException>(
+            async () => await factory.CreateAsync(session, CancellationToken.None).WaitAsync(TestTimeout));
+
+        Assert.Equal(WorkerClientErrorCode.ProtocolViolation, exception.ErrorCode);
+        Assert.True(launcher.Process.IsDisposed);
+    }
+
+    private static GatewayOptions CreateOptions()
+    {
+        return new GatewayOptions
+        {
+            Worker = new WorkerOptions
+            {
+                StartupTimeoutSeconds = 5,
+                ShutdownTimeoutSeconds = 5,
+                HeartbeatIntervalSeconds = 30,
+                HeartbeatGraceSeconds = 30,
+                MaxMessageBytes = WorkerFrameProtocolOptions.DefaultMaxMessageBytes,
+            },
+            Events = new EventOptions
+            {
+                QueueCapacity = 16,
+            },
+        };
+    }
+
+    private static GatewaySession CreateSession()
+    {
+        return new GatewaySession(
+            FakeWorkerHarness.DefaultSessionId,
+            GatewayContractInfo.DefaultBackendName,
+            $"mxaccessgw-session-fake-worker-{Guid.NewGuid():N}",
+            FakeWorkerHarness.DefaultNonce,
+            "test-client",
+            "fake-worker-session-test",
+            "client-correlation-1",
+            TestTimeout,
+            TestTimeout,
+            TestTimeout,
+            DateTimeOffset.UtcNow);
+    }
+
+    private static WorkerCommand CreateCommand(MxCommandKind kind)
+    {
+        return new WorkerCommand
+        {
+            Command = new MxCommand
+            {
+                Kind = kind,
+            },
+        };
+    }
+
+    private sealed class ScriptedFakeWorkerProcessLauncher : IWorkerProcessLauncher
+    {
+        public const int ProcessId = 2468;
+        private readonly FakeWorkerProcess _process = new(ProcessId);
+
+        public FakeWorkerHarness? Harness { get; private set; }
+
+        public Task<WorkerProcessHandle> LaunchAsync(
+            WorkerProcessLaunchRequest request,
+            CancellationToken cancellationToken = default)
+        {
+            _ = RunWorkerAsync(request, cancellationToken);
+
+            return Task.FromResult(CreateHandle(_process));
+        }
+
+        private async Task RunWorkerAsync(
+            WorkerProcessLaunchRequest request,
+            CancellationToken cancellationToken)
+        {
+            Harness = await FakeWorkerHarness.ConnectToGatewayPipeAsync(
+                request.SessionId,
+                request.Nonce,
+                request.PipeName,
+                request.ProtocolVersion,
+                cancellationToken: cancellationToken).ConfigureAwait(false);
+            await Harness.CompleteStartupAsync(ProcessId, cancellationToken: cancellationToken).ConfigureAwait(false);
+        }
+    }
+
+    private sealed class FailingStartupWorkerProcessLauncher : IWorkerProcessLauncher
+    {
+        public FakeWorkerProcess Process { get; } = new(processId: 3579);
+
+        public Task<WorkerProcessHandle> LaunchAsync(
+            WorkerProcessLaunchRequest request,
+            CancellationToken cancellationToken = default)
+        {
+            _ = RunWorkerAsync(request, cancellationToken);
+
+            return Task.FromResult(CreateHandle(Process));
+        }
+
+        private async Task RunWorkerAsync(
+            WorkerProcessLaunchRequest request,
+            CancellationToken cancellationToken)
+        {
+            await using FakeWorkerHarness harness = await FakeWorkerHarness.ConnectToGatewayPipeAsync(
+                request.SessionId,
+                request.Nonce,
+                request.PipeName,
+                request.ProtocolVersion,
+                cancellationToken: cancellationToken).ConfigureAwait(false);
+            _ = await harness.ReadGatewayEnvelopeAsync(cancellationToken).ConfigureAwait(false);
+            await harness.SendWorkerHelloAsync(
+                workerProcessId: Process.Id,
+                workerProtocolVersion: request.ProtocolVersion + 1,
+                cancellationToken: cancellationToken).ConfigureAwait(false);
+        }
+    }
+
+    private static WorkerProcessHandle CreateHandle(IWorkerProcess process)
+    {
+        return new WorkerProcessHandle(
+            process,
+            new WorkerProcessCommandLine("fake-worker.exe", []),
+            DateTimeOffset.UtcNow);
+    }
+
+    private sealed class FakeWorkerProcess(int processId) : IWorkerProcess
+    {
+        private bool _disposed;
+
+        public int Id { get; } = processId;
+
+        public bool HasExited { get; private set; }
+
+        public int? ExitCode { get; private set; }
+
+        public int KillCount { get; private set; }
+
+        public ValueTask WaitForExitAsync(CancellationToken cancellationToken)
+        {
+            HasExited = true;
+            ExitCode = 0;
+            return ValueTask.CompletedTask;
+        }
+
+        public void Kill(bool entireProcessTree)
+        {
+            KillCount++;
+            HasExited = true;
+            ExitCode = -1;
+        }
+
+        public void Dispose()
+        {
+            _disposed = true;
+        }
+
+        public bool IsDisposed => _disposed;
+    }
+}

src/MxGateway.Tests/Gateway/Workers/FakeWorkerHarnessTests.cs

@@ -0,0 +1,209 @@
+using MxGateway.Contracts;
+using MxGateway.Contracts.Proto;
+using MxGateway.Server.Workers;
+using MxGateway.Tests.Gateway.Workers.Fakes;
+
+namespace MxGateway.Tests.Gateway.Workers;
+
+public sealed class FakeWorkerHarnessTests
+{
+    private static readonly TimeSpan TestTimeout = TimeSpan.FromSeconds(5);
+
+    [Fact]
+    public async Task CompleteStartupAsync_WithHelloAndReady_TransitionsClientToReady()
+    {
+        await using FakeWorkerHarness fakeWorker = await FakeWorkerHarness.CreateConnectedPairAsync();
+        await using WorkerClient client = fakeWorker.CreateClient();
+
+        Task startTask = client.StartAsync(CancellationToken.None);
+        WorkerEnvelope gatewayHello = await fakeWorker.CompleteStartupAsync();
+        await startTask.WaitAsync(TestTimeout);
+
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.GatewayHello, gatewayHello.BodyCase);
+        Assert.Equal(FakeWorkerHarness.DefaultNonce, gatewayHello.GatewayHello.Nonce);
+        Assert.Equal(WorkerClientState.Ready, client.State);
+        Assert.Equal(FakeWorkerHarness.DefaultWorkerProcessId, client.ProcessId);
+    }
+
+    [Fact]
+    public async Task StartAsync_WithProtocolMismatch_FailsStartup()
+    {
+        await using FakeWorkerHarness fakeWorker = await FakeWorkerHarness.CreateConnectedPairAsync();
+        await using WorkerClient client = fakeWorker.CreateClient();
+
+        Task startTask = client.StartAsync(CancellationToken.None);
+        WorkerEnvelope gatewayHello = await fakeWorker.ReadGatewayEnvelopeAsync();
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.GatewayHello, gatewayHello.BodyCase);
+        await fakeWorker.SendWorkerHelloAsync(
+            workerProtocolVersion: GatewayContractInfo.WorkerProtocolVersion + 1);
+
+        WorkerClientException exception = await Assert.ThrowsAsync<WorkerClientException>(
+            async () => await startTask.WaitAsync(TestTimeout));
+
+        Assert.Equal(WorkerClientErrorCode.ProtocolViolation, exception.ErrorCode);
+    }
+
+    [Fact]
+    public async Task InvokeAsync_WithScriptedReply_CompletesCommand()
+    {
+        await using FakeWorkerHarness fakeWorker = await FakeWorkerHarness.CreateConnectedPairAsync();
+        await using WorkerClient client = fakeWorker.CreateClient();
+        await StartClientAsync(fakeWorker, client);
+
+        Task<WorkerCommandReply> invokeTask = client.InvokeAsync(
+            CreateCommand(MxCommandKind.Ping),
+            TestTimeout,
+            CancellationToken.None);
+        WorkerEnvelope commandEnvelope = await fakeWorker.ReadCommandAsync();
+        await fakeWorker.ReplyToCommandAsync(commandEnvelope);
+
+        WorkerCommandReply reply = await invokeTask.WaitAsync(TestTimeout);
+
+        Assert.Equal(commandEnvelope.CorrelationId, reply.Reply.CorrelationId);
+        Assert.Equal(MxCommandKind.Ping, reply.Reply.Kind);
+        Assert.Equal(ProtocolStatusCode.Ok, reply.Reply.ProtocolStatus.Code);
+    }
+
+    [Fact]
+    public async Task ReadEventsAsync_WithScriptedEvents_YieldsOrderedEvents()
+    {
+        await using FakeWorkerHarness fakeWorker = await FakeWorkerHarness.CreateConnectedPairAsync();
+        await using WorkerClient client = fakeWorker.CreateClient();
+        await StartClientAsync(fakeWorker, client);
+        using CancellationTokenSource cancellationTokenSource = new(TestTimeout);
+
+        await using IAsyncEnumerator<WorkerEvent> events =
+            client.ReadEventsAsync(cancellationTokenSource.Token).GetAsyncEnumerator(cancellationTokenSource.Token);
+
+        await fakeWorker.EmitEventAsync(MxEventFamily.OnDataChange, cancellationTokenSource.Token);
+        await fakeWorker.EmitEventAsync(MxEventFamily.OperationComplete, cancellationTokenSource.Token);
+
+        Assert.True(await events.MoveNextAsync());
+        Assert.Equal((ulong)3, events.Current.Event.WorkerSequence);
+        Assert.Equal(MxEventFamily.OnDataChange, events.Current.Event.Family);
+
+        Assert.True(await events.MoveNextAsync());
+        Assert.Equal((ulong)4, events.Current.Event.WorkerSequence);
+        Assert.Equal(MxEventFamily.OperationComplete, events.Current.Event.Family);
+    }
+
+    [Fact]
+    public async Task ReadLoop_WithScriptedFault_FaultsClient()
+    {
+        await using FakeWorkerHarness fakeWorker = await FakeWorkerHarness.CreateConnectedPairAsync();
+        await using WorkerClient client = fakeWorker.CreateClient();
+        await StartClientAsync(fakeWorker, client);
+
+        await fakeWorker.EmitFaultAsync(
+            WorkerFaultCategory.MxaccessCommandFailed,
+            "scripted MXAccess command fault");
+
+        await WaitUntilAsync(
+            () => client.State == WorkerClientState.Faulted,
+            TestTimeout);
+
+        Assert.Equal(WorkerClientState.Faulted, client.State);
+    }
+
+    [Fact]
+    public async Task SendHeartbeatAsync_UpdatesClientHeartbeatState()
+    {
+        await using FakeWorkerHarness fakeWorker = await FakeWorkerHarness.CreateConnectedPairAsync();
+        await using WorkerClient client = fakeWorker.CreateClient();
+        await StartClientAsync(fakeWorker, client);
+        DateTimeOffset previousHeartbeat = client.LastHeartbeatAt;
+
+        await Task.Delay(TimeSpan.FromMilliseconds(20));
+        await fakeWorker.SendHeartbeatAsync(
+            configureHeartbeat: heartbeat => heartbeat.WorkerProcessId = 2468);
+
+        await WaitUntilAsync(
+            () => client.ProcessId == 2468 && client.LastHeartbeatAt > previousHeartbeat,
+            TestTimeout);
+
+        Assert.Equal(WorkerClientState.Ready, client.State);
+    }
+
+    [Fact]
+    public async Task InvokeAsync_WithHungWorker_TimesOutPendingCommand()
+    {
+        await using FakeWorkerHarness fakeWorker = await FakeWorkerHarness.CreateConnectedPairAsync();
+        await using WorkerClient client = fakeWorker.CreateClient();
+        await StartClientAsync(fakeWorker, client);
+
+        Task<WorkerCommandReply> invokeTask = client.InvokeAsync(
+            CreateCommand(MxCommandKind.Ping),
+            TimeSpan.FromMilliseconds(50),
+            CancellationToken.None);
+        WorkerEnvelope commandEnvelope = await fakeWorker.ReadCommandAsync();
+
+        WorkerClientException exception = await Assert.ThrowsAsync<WorkerClientException>(
+            async () => await invokeTask.WaitAsync(TestTimeout));
+
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerCommand, commandEnvelope.BodyCase);
+        Assert.Equal(WorkerClientErrorCode.CommandTimeout, exception.ErrorCode);
+    }
+
+    [Fact]
+    public async Task ReadLoop_WithMalformedFrame_FaultsClient()
+    {
+        await using FakeWorkerHarness fakeWorker = await FakeWorkerHarness.CreateConnectedPairAsync();
+        await using WorkerClient client = fakeWorker.CreateClient();
+        await StartClientAsync(fakeWorker, client);
+
+        await fakeWorker.WriteMalformedPayloadAsync(new byte[] { 0x08, 0x96, 0x01 });
+
+        await WaitUntilAsync(
+            () => client.State == WorkerClientState.Faulted,
+            TestTimeout);
+
+        Assert.Equal(WorkerClientState.Faulted, client.State);
+    }
+
+    [Fact]
+    public async Task ShutdownAsync_WithShutdownAck_ClosesClient()
+    {
+        await using FakeWorkerHarness fakeWorker = await FakeWorkerHarness.CreateConnectedPairAsync();
+        await using WorkerClient client = fakeWorker.CreateClient();
+        await StartClientAsync(fakeWorker, client);
+
+        Task shutdownTask = client.ShutdownAsync(TestTimeout, CancellationToken.None);
+        WorkerEnvelope shutdownEnvelope = await fakeWorker.ReadShutdownAsync();
+        await fakeWorker.SendShutdownAckAsync();
+        await shutdownTask.WaitAsync(TestTimeout);
+
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerShutdown, shutdownEnvelope.BodyCase);
+        Assert.Equal(WorkerClientState.Closed, client.State);
+    }
+
+    private static async Task StartClientAsync(
+        FakeWorkerHarness fakeWorker,
+        WorkerClient client)
+    {
+        Task startTask = client.StartAsync(CancellationToken.None);
+        await fakeWorker.CompleteStartupAsync().ConfigureAwait(false);
+        await startTask.WaitAsync(TestTimeout).ConfigureAwait(false);
+    }
+
+    private static WorkerCommand CreateCommand(MxCommandKind kind)
+    {
+        return new WorkerCommand
+        {
+            Command = new MxCommand
+            {
+                Kind = kind,
+            },
+        };
+    }
+
+    private static async Task WaitUntilAsync(
+        Func<bool> predicate,
+        TimeSpan timeout)
+    {
+        using CancellationTokenSource cancellationTokenSource = new(timeout);
+        while (!predicate())
+        {
+            await Task.Delay(TimeSpan.FromMilliseconds(10), cancellationTokenSource.Token);
+        }
+    }
+}

src/MxGateway.Tests/Gateway/Workers/Fakes/FakeWorkerHarness.cs

@@ -0,0 +1,406 @@
+using System.Buffers.Binary;
+using System.IO.Pipes;
+using Google.Protobuf.WellKnownTypes;
+using MxGateway.Contracts;
+using MxGateway.Contracts.Proto;
+using MxGateway.Server.Metrics;
+using MxGateway.Server.Workers;
+
+namespace MxGateway.Tests.Gateway.Workers.Fakes;
+
+public sealed class FakeWorkerHarness : IAsyncDisposable
+{
+    public const string DefaultSessionId = "session-fake-worker";
+    public const string DefaultNonce = "nonce-fake-worker";
+    public const int DefaultWorkerProcessId = 9321;
+
+    private readonly NamedPipeServerStream? _gatewayStream;
+    private readonly NamedPipeClientStream _workerStream;
+    private readonly WorkerFrameProtocolOptions _frameOptions;
+    private readonly WorkerFrameReader _reader;
+    private readonly WorkerFrameWriter _writer;
+    private bool _workerSideDisposed;
+
+    private FakeWorkerHarness(
+        string sessionId,
+        string nonce,
+        NamedPipeServerStream? gatewayStream,
+        NamedPipeClientStream workerStream,
+        WorkerFrameProtocolOptions frameOptions)
+    {
+        SessionId = sessionId;
+        Nonce = nonce;
+        _gatewayStream = gatewayStream;
+        _workerStream = workerStream;
+        _frameOptions = frameOptions;
+        _reader = new WorkerFrameReader(_workerStream, frameOptions);
+        _writer = new WorkerFrameWriter(_workerStream, frameOptions);
+    }
+
+    public string SessionId { get; }
+
+    public string Nonce { get; }
+
+    public ulong NextWorkerSequence { get; private set; }
+
+    public static async Task<FakeWorkerHarness> CreateConnectedPairAsync(
+        string sessionId = DefaultSessionId,
+        string nonce = DefaultNonce,
+        uint protocolVersion = GatewayContractInfo.WorkerProtocolVersion,
+        int maxMessageBytes = WorkerFrameProtocolOptions.DefaultMaxMessageBytes,
+        CancellationToken cancellationToken = default)
+    {
+        string pipeName = $"mxaccessgw-fake-worker-{Guid.NewGuid():N}";
+        NamedPipeServerStream gatewayStream = new(
+            pipeName,
+            PipeDirection.InOut,
+            maxNumberOfServerInstances: 1,
+            PipeTransmissionMode.Byte,
+            PipeOptions.Asynchronous);
+        NamedPipeClientStream workerStream = CreateWorkerStream(pipeName);
+
+        Task waitForConnectionTask = gatewayStream.WaitForConnectionAsync(cancellationToken);
+        await workerStream.ConnectAsync(cancellationToken).ConfigureAwait(false);
+        await waitForConnectionTask.ConfigureAwait(false);
+
+        return new FakeWorkerHarness(
+            sessionId,
+            nonce,
+            gatewayStream,
+            workerStream,
+            new WorkerFrameProtocolOptions(sessionId, protocolVersion, maxMessageBytes));
+    }
+
+    public static async Task<FakeWorkerHarness> ConnectToGatewayPipeAsync(
+        string sessionId,
+        string nonce,
+        string pipeName,
+        uint protocolVersion = GatewayContractInfo.WorkerProtocolVersion,
+        int maxMessageBytes = WorkerFrameProtocolOptions.DefaultMaxMessageBytes,
+        CancellationToken cancellationToken = default)
+    {
+        NamedPipeClientStream workerStream = CreateWorkerStream(pipeName);
+        await workerStream.ConnectAsync(cancellationToken).ConfigureAwait(false);
+
+        return new FakeWorkerHarness(
+            sessionId,
+            nonce,
+            gatewayStream: null,
+            workerStream,
+            new WorkerFrameProtocolOptions(sessionId, protocolVersion, maxMessageBytes));
+    }
+
+    public WorkerClient CreateClient(
+        WorkerClientOptions? options = null,
+        GatewayMetrics? metrics = null,
+        TimeProvider? timeProvider = null)
+    {
+        if (_gatewayStream is null)
+        {
+            throw new InvalidOperationException("This fake worker is connected to a gateway-owned pipe.");
+        }
+
+        WorkerClientConnection connection = new(
+            SessionId,
+            Nonce,
+            _gatewayStream,
+            _frameOptions);
+
+        return new WorkerClient(connection, options, metrics, timeProvider);
+    }
+
+    public async Task<WorkerEnvelope> CompleteStartupAsync(
+        int workerProcessId = DefaultWorkerProcessId,
+        string workerVersion = "fake-worker",
+        string mxaccessProgid = "LMXProxy.LMXProxyServer.1",
+        string mxaccessClsid = "{C30B52F5-2CB5-4760-AF0A-3A344A7EB5DC}",
+        CancellationToken cancellationToken = default)
+    {
+        WorkerEnvelope gatewayHello = await ReadGatewayEnvelopeAsync(cancellationToken).ConfigureAwait(false);
+        if (gatewayHello.BodyCase != WorkerEnvelope.BodyOneofCase.GatewayHello)
+        {
+            throw new InvalidOperationException($"Expected GatewayHello but received {gatewayHello.BodyCase}.");
+        }
+
+        await SendWorkerHelloAsync(
+            workerProcessId,
+            workerVersion,
+            cancellationToken: cancellationToken).ConfigureAwait(false);
+        await SendWorkerReadyAsync(
+            workerProcessId,
+            mxaccessProgid,
+            mxaccessClsid,
+            cancellationToken).ConfigureAwait(false);
+
+        return gatewayHello;
+    }
+
+    public async Task<WorkerEnvelope> ReadGatewayEnvelopeAsync(CancellationToken cancellationToken = default)
+    {
+        return await _reader.ReadAsync(cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task<WorkerEnvelope> ReadCommandAsync(CancellationToken cancellationToken = default)
+    {
+        WorkerEnvelope envelope = await ReadGatewayEnvelopeAsync(cancellationToken).ConfigureAwait(false);
+        if (envelope.BodyCase != WorkerEnvelope.BodyOneofCase.WorkerCommand)
+        {
+            throw new InvalidOperationException($"Expected WorkerCommand but received {envelope.BodyCase}.");
+        }
+
+        return envelope;
+    }
+
+    public async Task<WorkerEnvelope> ReadShutdownAsync(CancellationToken cancellationToken = default)
+    {
+        WorkerEnvelope envelope = await ReadGatewayEnvelopeAsync(cancellationToken).ConfigureAwait(false);
+        if (envelope.BodyCase != WorkerEnvelope.BodyOneofCase.WorkerShutdown)
+        {
+            throw new InvalidOperationException($"Expected WorkerShutdown but received {envelope.BodyCase}.");
+        }
+
+        return envelope;
+    }
+
+    public async Task SendWorkerHelloAsync(
+        int workerProcessId = DefaultWorkerProcessId,
+        string workerVersion = "fake-worker",
+        uint? workerProtocolVersion = null,
+        string? nonce = null,
+        CancellationToken cancellationToken = default)
+    {
+        await _writer.WriteAsync(
+            CreateEnvelope(
+                correlationId: string.Empty,
+                envelope => envelope.WorkerHello = new WorkerHello
+                {
+                    ProtocolVersion = workerProtocolVersion ?? _frameOptions.ProtocolVersion,
+                    Nonce = nonce ?? Nonce,
+                    WorkerProcessId = workerProcessId,
+                    WorkerVersion = workerVersion,
+                }),
+            cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task SendWorkerReadyAsync(
+        int workerProcessId = DefaultWorkerProcessId,
+        string mxaccessProgid = "LMXProxy.LMXProxyServer.1",
+        string mxaccessClsid = "{C30B52F5-2CB5-4760-AF0A-3A344A7EB5DC}",
+        CancellationToken cancellationToken = default)
+    {
+        await _writer.WriteAsync(
+            CreateEnvelope(
+                correlationId: string.Empty,
+                envelope => envelope.WorkerReady = new WorkerReady
+                {
+                    WorkerProcessId = workerProcessId,
+                    MxaccessProgid = mxaccessProgid,
+                    MxaccessClsid = mxaccessClsid,
+                    ReadyTimestamp = Timestamp.FromDateTimeOffset(DateTimeOffset.UtcNow),
+                }),
+            cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task ReplyToCommandAsync(
+        WorkerEnvelope commandEnvelope,
+        ProtocolStatusCode statusCode = ProtocolStatusCode.Ok,
+        string statusMessage = "OK",
+        Action<MxCommandReply>? configureReply = null,
+        CancellationToken cancellationToken = default)
+    {
+        if (commandEnvelope.BodyCase != WorkerEnvelope.BodyOneofCase.WorkerCommand)
+        {
+            throw new ArgumentException("Command envelope must contain WorkerCommand.", nameof(commandEnvelope));
+        }
+
+        MxCommandKind kind = commandEnvelope.WorkerCommand.Command?.Kind ?? MxCommandKind.Unspecified;
+        MxCommandReply reply = new()
+        {
+            SessionId = SessionId,
+            CorrelationId = commandEnvelope.CorrelationId,
+            Kind = kind,
+            ProtocolStatus = new ProtocolStatus
+            {
+                Code = statusCode,
+                Message = statusMessage,
+            },
+        };
+        configureReply?.Invoke(reply);
+
+        await _writer.WriteAsync(
+            CreateEnvelope(
+                commandEnvelope.CorrelationId,
+                envelope => envelope.WorkerCommandReply = new WorkerCommandReply
+                {
+                    Reply = reply,
+                    CompletedTimestamp = Timestamp.FromDateTimeOffset(DateTimeOffset.UtcNow),
+                }),
+            cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task EmitEventAsync(
+        MxEventFamily family,
+        CancellationToken cancellationToken = default,
+        Action<MxEvent>? configureEvent = null)
+    {
+        ulong sequence = NextWorkerSequence + 1;
+        MxEvent mxEvent = new()
+        {
+            SessionId = SessionId,
+            Family = family,
+            WorkerSequence = sequence,
+            WorkerTimestamp = Timestamp.FromDateTimeOffset(DateTimeOffset.UtcNow),
+        };
+        configureEvent?.Invoke(mxEvent);
+
+        await _writer.WriteAsync(
+            CreateEnvelope(
+                correlationId: string.Empty,
+                envelope => envelope.WorkerEvent = new WorkerEvent
+                {
+                    Event = mxEvent,
+                }),
+            cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task EmitFaultAsync(
+        WorkerFaultCategory category,
+        string diagnosticMessage,
+        CancellationToken cancellationToken = default)
+    {
+        await _writer.WriteAsync(
+            CreateEnvelope(
+                correlationId: string.Empty,
+                envelope => envelope.WorkerFault = new WorkerFault
+                {
+                    Category = category,
+                    DiagnosticMessage = diagnosticMessage,
+                    ProtocolStatus = new ProtocolStatus
+                    {
+                        Code = ProtocolStatusCode.WorkerUnavailable,
+                        Message = diagnosticMessage,
+                    },
+                }),
+            cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task SendHeartbeatAsync(
+        WorkerState state = WorkerState.Ready,
+        CancellationToken cancellationToken = default,
+        Action<WorkerHeartbeat>? configureHeartbeat = null)
+    {
+        WorkerHeartbeat heartbeat = new()
+        {
+            WorkerProcessId = DefaultWorkerProcessId,
+            State = state,
+            LastStaActivityTimestamp = Timestamp.FromDateTimeOffset(DateTimeOffset.UtcNow),
+        };
+        configureHeartbeat?.Invoke(heartbeat);
+
+        await _writer.WriteAsync(
+            CreateEnvelope(
+                correlationId: string.Empty,
+                envelope => envelope.WorkerHeartbeat = heartbeat),
+            cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task SendShutdownAckAsync(
+        ProtocolStatusCode statusCode = ProtocolStatusCode.Ok,
+        CancellationToken cancellationToken = default)
+    {
+        await _writer.WriteAsync(
+            CreateEnvelope(
+                correlationId: string.Empty,
+                envelope => envelope.WorkerShutdownAck = new WorkerShutdownAck
+                {
+                    Status = new ProtocolStatus
+                    {
+                        Code = statusCode,
+                        Message = statusCode.ToString(),
+                    },
+                }),
+            cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task WriteMalformedPayloadAsync(
+        ReadOnlyMemory<byte> payload,
+        CancellationToken cancellationToken = default)
+    {
+        if (payload.IsEmpty)
+        {
+            throw new ArgumentException("Malformed payload must include at least one byte.", nameof(payload));
+        }
+
+        byte[] lengthPrefix = new byte[sizeof(uint)];
+        BinaryPrimitives.WriteUInt32LittleEndian(lengthPrefix, (uint)payload.Length);
+        await _workerStream.WriteAsync(lengthPrefix, cancellationToken).ConfigureAwait(false);
+        await _workerStream.WriteAsync(payload, cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task WriteOversizedFrameHeaderAsync(
+        uint payloadLength,
+        CancellationToken cancellationToken = default)
+    {
+        if (payloadLength <= _frameOptions.MaxMessageBytes)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(payloadLength),
+                payloadLength,
+                "Payload length must exceed the configured maximum.");
+        }
+
+        byte[] lengthPrefix = new byte[sizeof(uint)];
+        BinaryPrimitives.WriteUInt32LittleEndian(lengthPrefix, payloadLength);
+        await _workerStream.WriteAsync(lengthPrefix, cancellationToken).ConfigureAwait(false);
+    }
+
+    public async ValueTask DisposeWorkerSideAsync()
+    {
+        if (_workerSideDisposed)
+        {
+            return;
+        }
+
+        await _workerStream.DisposeAsync().ConfigureAwait(false);
+        _workerSideDisposed = true;
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await DisposeWorkerSideAsync().ConfigureAwait(false);
+        if (_gatewayStream is not null)
+        {
+            await _gatewayStream.DisposeAsync().ConfigureAwait(false);
+        }
+    }
+
+    private WorkerEnvelope CreateEnvelope(
+        string correlationId,
+        Action<WorkerEnvelope> setBody)
+    {
+        WorkerEnvelope envelope = new()
+        {
+            ProtocolVersion = _frameOptions.ProtocolVersion,
+            SessionId = SessionId,
+            Sequence = AdvanceSequence(),
+            CorrelationId = correlationId,
+        };
+        setBody(envelope);
+
+        return envelope;
+    }
+
+    private ulong AdvanceSequence()
+    {
+        return ++NextWorkerSequence;
+    }
+
+    private static NamedPipeClientStream CreateWorkerStream(string pipeName)
+    {
+        return new NamedPipeClientStream(
+            ".",
+            pipeName,
+            PipeDirection.InOut,
+            PipeOptions.Asynchronous);
+    }
+}

src/MxGateway.Tests/Gateway/Workers/WorkerClientTests.cs

@@ -1,4 +1,5 @@
 using System.IO.Pipes;
+using Google.Protobuf.WellKnownTypes;
 using MxGateway.Contracts;
 using MxGateway.Contracts.Proto;
 using MxGateway.Server.Workers;
@@ -151,6 +152,24 @@ public sealed class WorkerClientTests
         Assert.Equal(WorkerClientState.Faulted, client.State);
     }
 
+    [Fact]
+    public async Task ReadLoop_WhenHeartbeatArrives_UpdatesLastHeartbeatAndWorkerProcess()
+    {
+        await using PipePair pipePair = await PipePair.CreateAsync();
+        await using WorkerClient client = CreateClient(pipePair);
+        await CompleteHandshakeAsync(client, pipePair);
+        DateTimeOffset previousHeartbeat = client.LastHeartbeatAt;
+
+        await Task.Delay(TimeSpan.FromMilliseconds(20));
+        await pipePair.WorkerWriter.WriteAsync(CreateHeartbeatEnvelope(workerProcessId: 9876));
+
+        await WaitUntilAsync(
+            () => client.ProcessId == 9876 && client.LastHeartbeatAt > previousHeartbeat,
+            TestTimeout);
+
+        Assert.Equal(WorkerClientState.Ready, client.State);
+    }
+
     [Fact]
     public async Task HeartbeatMonitor_WhenHeartbeatExpires_FaultsClient()
     {
@@ -276,6 +295,21 @@ public sealed class WorkerClientTests
             });
     }
 
+    private static WorkerEnvelope CreateHeartbeatEnvelope(int workerProcessId)
+    {
+        return CreateWorkerEnvelope(
+            correlationId: string.Empty,
+            sequence: 20,
+            envelope => envelope.WorkerHeartbeat = new WorkerHeartbeat
+            {
+                WorkerProcessId = workerProcessId,
+                State = WorkerState.Ready,
+                LastStaActivityTimestamp = Timestamp.FromDateTimeOffset(DateTimeOffset.UtcNow),
+                PendingCommandCount = 0,
+                OutboundEventQueueDepth = 0,
+            });
+    }
+
     private static WorkerEnvelope CreateWorkerEnvelope(
         string correlationId,
         ulong sequence,

src/MxGateway.Worker.Tests/Bootstrap/WorkerApplicationTests.cs

@@ -30,7 +30,7 @@ public sealed class WorkerApplicationTests
         Assert.Equal("mxaccess-gateway-123-session-1", entry.Fields["pipe_name"]);
         Assert.Equal(GatewayContractInfo.WorkerProtocolVersion, entry.Fields["protocol_version"]);
         Assert.Equal("[redacted]", entry.Fields["nonce"]);
-        Assert.Equal("WorkerPipeHandshakeSucceeded", logger.Entries[1].EventName);
+        Assert.Equal("WorkerPipeSessionCompleted", logger.Entries[1].EventName);
     }
 
     [Fact]

src/MxGateway.Worker.Tests/Ipc/WorkerPipeClientTests.cs

@@ -1,10 +1,15 @@
 using System;
+using System.IO;
 using System.IO.Pipes;
+using System.Threading;
 using System.Threading.Tasks;
+using Google.Protobuf.WellKnownTypes;
 using MxGateway.Contracts;
 using MxGateway.Contracts.Proto;
 using MxGateway.Worker.Bootstrap;
 using MxGateway.Worker.Ipc;
+using MxGateway.Worker.MxAccess;
+using MxGateway.Worker.Sta;
 
 namespace MxGateway.Worker.Tests.Ipc;
 
@@ -28,7 +33,9 @@ public sealed class WorkerPipeClientTests
             PipeTransmissionMode.Byte,
             PipeOptions.Asynchronous);
 
-        WorkerPipeClient client = new(connectTimeoutMilliseconds: 5000);
+        WorkerPipeClient client = new(
+            connectTimeoutMilliseconds: 5000,
+            (stream, options) => CreateSession(stream, options));
         Task clientTask = client.RunAsync(workerOptions);
 
         await Task.Factory.FromAsync(server.BeginWaitForConnection, server.EndWaitForConnection, null);
@@ -56,6 +63,86 @@ public sealed class WorkerPipeClientTests
         WorkerEnvelope ready = await reader.ReadAsync();
         Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerReady, ready.BodyCase);
 
+        await writer.WriteAsync(new WorkerEnvelope
+        {
+            ProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
+            SessionId = "session-1",
+            Sequence = 2,
+            WorkerShutdown = new WorkerShutdown
+            {
+                GracePeriod = Duration.FromTimeSpan(TimeSpan.FromSeconds(1)),
+                Reason = "test-complete",
+            },
+        });
+
+        WorkerEnvelope shutdownAck = await reader.ReadAsync();
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerShutdownAck, shutdownAck.BodyCase);
         await clientTask;
     }
+
+    private static WorkerPipeSession CreateSession(
+        Stream stream,
+        WorkerFrameProtocolOptions options)
+    {
+        return new WorkerPipeSession(
+            new WorkerFrameReader(stream, options),
+            new WorkerFrameWriter(stream, options),
+            options,
+            () => 1234,
+            new WorkerPipeSessionOptions
+            {
+                HeartbeatInterval = TimeSpan.FromSeconds(30),
+                HeartbeatGrace = TimeSpan.FromSeconds(30),
+            },
+            () => new FakeRuntimeSession());
+    }
+
+    private sealed class FakeRuntimeSession : IWorkerRuntimeSession
+    {
+        public Task<WorkerReady> StartAsync(
+            int workerProcessId,
+            CancellationToken cancellationToken = default)
+        {
+            return Task.FromResult(new WorkerReady
+            {
+                WorkerProcessId = workerProcessId,
+                MxaccessProgid = MxGateway.Worker.MxAccess.MxAccessInteropInfo.ProgId,
+                MxaccessClsid = MxGateway.Worker.MxAccess.MxAccessInteropInfo.Clsid,
+                ReadyTimestamp = Timestamp.FromDateTimeOffset(DateTimeOffset.UtcNow),
+            });
+        }
+
+        public Task<MxCommandReply> DispatchAsync(StaCommand command)
+        {
+            return Task.FromResult(new MxCommandReply
+            {
+                SessionId = command.SessionId,
+                CorrelationId = command.CorrelationId,
+                Kind = command.Kind,
+                ProtocolStatus = new ProtocolStatus
+                {
+                    Code = ProtocolStatusCode.Ok,
+                    Message = "OK",
+                },
+            });
+        }
+
+        public WorkerRuntimeHeartbeatSnapshot CaptureHeartbeat()
+        {
+            return new WorkerRuntimeHeartbeatSnapshot(
+                DateTimeOffset.UtcNow,
+                pendingCommandCount: 0,
+                outboundEventQueueDepth: 0,
+                lastEventSequence: 0,
+                currentCommandCorrelationId: string.Empty);
+        }
+
+        public void RequestShutdown()
+        {
+        }
+
+        public void Dispose()
+        {
+        }
+    }
 }

src/MxGateway.Worker.Tests/Ipc/WorkerPipeSessionTests.cs

@@ -1,11 +1,16 @@
+using System;
 using System.Collections.Generic;
 using System.IO;
+using System.IO.Pipes;
 using System.Runtime.InteropServices;
 using System.Threading;
 using System.Threading.Tasks;
+using Google.Protobuf.WellKnownTypes;
 using MxGateway.Contracts;
 using MxGateway.Contracts.Proto;
 using MxGateway.Worker.Ipc;
+using MxGateway.Worker.MxAccess;
+using MxGateway.Worker.Sta;
 
 namespace MxGateway.Worker.Tests.Ipc;
 
@@ -147,6 +152,127 @@ public sealed class WorkerPipeSessionTests
         Assert.Equal(ProtocolStatusCode.WorkerUnavailable, written[1].WorkerFault.ProtocolStatus.Code);
     }
 
+    [Fact]
+    public async Task RunAsync_SendsHeartbeatPayloadFromRuntimeSnapshot()
+    {
+        using CancellationTokenSource cancellation = new(TimeSpan.FromSeconds(5));
+        using PipePair pipePair = await PipePair.CreateAsync(cancellation.Token);
+        FakeRuntimeSession runtime = new();
+        runtime.SetSnapshot(new WorkerRuntimeHeartbeatSnapshot(
+            DateTimeOffset.UtcNow,
+            pendingCommandCount: 2,
+            outboundEventQueueDepth: 3,
+            lastEventSequence: 42,
+            currentCommandCorrelationId: "current-command"));
+        WorkerPipeSession session = CreatePipeSession(
+            pipePair.WorkerStream,
+            runtime,
+            new WorkerPipeSessionOptions
+            {
+                HeartbeatInterval = TimeSpan.FromMilliseconds(20),
+                HeartbeatGrace = TimeSpan.FromSeconds(5),
+            });
+        Task runTask = session.RunAsync(cancellation.Token);
+
+        await CompleteGatewayHandshakeAsync(pipePair, cancellation.Token);
+        await ThrowIfCompletedAsync(runTask);
+
+        WorkerEnvelope heartbeat = await ReadUntilAsync(
+            pipePair.GatewayReader,
+            WorkerEnvelope.BodyOneofCase.WorkerHeartbeat,
+            cancellation.Token);
+
+        Assert.Equal(WorkerState.ExecutingCommand, heartbeat.WorkerHeartbeat.State);
+        Assert.Equal(1234, heartbeat.WorkerHeartbeat.WorkerProcessId);
+        Assert.Equal(2u, heartbeat.WorkerHeartbeat.PendingCommandCount);
+        Assert.Equal(3u, heartbeat.WorkerHeartbeat.OutboundEventQueueDepth);
+        Assert.Equal(42UL, heartbeat.WorkerHeartbeat.LastEventSequence);
+        Assert.Equal("current-command", heartbeat.WorkerHeartbeat.CurrentCommandCorrelationId);
+
+        await SendShutdownAndWaitAsync(pipePair, runTask, cancellation.Token);
+    }
+
+    [Fact]
+    public async Task RunAsync_WhenCommandIsExecuting_HeartbeatReportsCurrentCorrelation()
+    {
+        using CancellationTokenSource cancellation = new(TimeSpan.FromSeconds(5));
+        using PipePair pipePair = await PipePair.CreateAsync(cancellation.Token);
+        FakeRuntimeSession runtime = new()
+        {
+            BlockDispatch = true,
+        };
+        WorkerPipeSession session = CreatePipeSession(
+            pipePair.WorkerStream,
+            runtime,
+            new WorkerPipeSessionOptions
+            {
+                HeartbeatInterval = TimeSpan.FromMilliseconds(20),
+                HeartbeatGrace = TimeSpan.FromSeconds(5),
+            });
+        Task runTask = session.RunAsync(cancellation.Token);
+        await CompleteGatewayHandshakeAsync(pipePair, cancellation.Token);
+
+        await pipePair.GatewayWriter.WriteAsync(
+            CreateCommandEnvelope("command-1"),
+            cancellation.Token);
+
+        Assert.True(runtime.DispatchStarted.Wait(TimeSpan.FromSeconds(2)));
+        WorkerEnvelope heartbeat = await ReadUntilAsync(
+            pipePair.GatewayReader,
+            WorkerEnvelope.BodyOneofCase.WorkerHeartbeat,
+            envelope => envelope.WorkerHeartbeat.CurrentCommandCorrelationId == "command-1",
+            cancellation.Token);
+
+        Assert.Equal("command-1", heartbeat.WorkerHeartbeat.CurrentCommandCorrelationId);
+        Assert.Equal(WorkerState.ExecutingCommand, heartbeat.WorkerHeartbeat.State);
+
+        runtime.ReleaseDispatch();
+        WorkerEnvelope reply = await ReadUntilAsync(
+            pipePair.GatewayReader,
+            WorkerEnvelope.BodyOneofCase.WorkerCommandReply,
+            cancellation.Token);
+
+        Assert.Equal("command-1", reply.CorrelationId);
+        Assert.Equal(ProtocolStatusCode.Ok, reply.WorkerCommandReply.Reply.ProtocolStatus.Code);
+
+        await SendShutdownAndWaitAsync(pipePair, runTask, cancellation.Token);
+    }
+
+    [Fact]
+    public async Task RunAsync_WhenStaActivityIsStale_WritesWatchdogFault()
+    {
+        using CancellationTokenSource cancellation = new(TimeSpan.FromSeconds(5));
+        using PipePair pipePair = await PipePair.CreateAsync(cancellation.Token);
+        FakeRuntimeSession runtime = new();
+        runtime.SetSnapshot(new WorkerRuntimeHeartbeatSnapshot(
+            DateTimeOffset.UtcNow - TimeSpan.FromSeconds(5),
+            pendingCommandCount: 0,
+            outboundEventQueueDepth: 0,
+            lastEventSequence: 0,
+            currentCommandCorrelationId: "stuck-command"));
+        WorkerPipeSession session = CreatePipeSession(
+            pipePair.WorkerStream,
+            runtime,
+            new WorkerPipeSessionOptions
+            {
+                HeartbeatInterval = TimeSpan.FromMilliseconds(20),
+                HeartbeatGrace = TimeSpan.FromMilliseconds(50),
+            });
+        Task runTask = session.RunAsync(cancellation.Token);
+        await CompleteGatewayHandshakeAsync(pipePair, cancellation.Token);
+
+        WorkerEnvelope fault = await ReadUntilAsync(
+            pipePair.GatewayReader,
+            WorkerEnvelope.BodyOneofCase.WorkerFault,
+            cancellation.Token);
+
+        Assert.Equal(WorkerFaultCategory.StaHung, fault.WorkerFault.Category);
+        Assert.Equal("stuck-command", fault.WorkerFault.CommandMethod);
+        Assert.Contains("STA activity is stale", fault.WorkerFault.DiagnosticMessage);
+
+        await SendShutdownAndWaitAsync(pipePair, runTask, cancellation.Token);
+    }
+
     private static WorkerPipeSession CreateSession(
         Stream inbound,
         Stream outbound,
@@ -159,6 +285,21 @@ public sealed class WorkerPipeSessionTests
             () => 1234);
     }
 
+    private static WorkerPipeSession CreatePipeSession(
+        Stream stream,
+        FakeRuntimeSession runtime,
+        WorkerPipeSessionOptions sessionOptions)
+    {
+        WorkerFrameProtocolOptions options = CreateOptions();
+        return new WorkerPipeSession(
+            new WorkerFrameReader(stream, options),
+            new WorkerFrameWriter(stream, options),
+            options,
+            () => 1234,
+            sessionOptions,
+            () => runtime);
+    }
+
     private static WorkerFrameProtocolOptions CreateOptions()
     {
         return new WorkerFrameProtocolOptions(
@@ -185,6 +326,119 @@ public sealed class WorkerPipeSessionTests
         };
     }
 
+    private static WorkerEnvelope CreateCommandEnvelope(string correlationId)
+    {
+        return new WorkerEnvelope
+        {
+            ProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
+            SessionId = SessionId,
+            Sequence = 2,
+            CorrelationId = correlationId,
+            WorkerCommand = new WorkerCommand
+            {
+                Command = new MxCommand
+                {
+                    Kind = MxCommandKind.Ping,
+                    Ping = new PingCommand
+                    {
+                        Message = "ping",
+                    },
+                },
+                EnqueueTimestamp = Timestamp.FromDateTimeOffset(DateTimeOffset.UtcNow),
+            },
+        };
+    }
+
+    private static WorkerEnvelope CreateShutdownEnvelope()
+    {
+        return new WorkerEnvelope
+        {
+            ProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
+            SessionId = SessionId,
+            Sequence = 3,
+            WorkerShutdown = new WorkerShutdown
+            {
+                GracePeriod = Duration.FromTimeSpan(TimeSpan.FromSeconds(1)),
+                Reason = "test-complete",
+            },
+        };
+    }
+
+    private static async Task CompleteGatewayHandshakeAsync(
+        PipePair pipePair,
+        CancellationToken cancellationToken)
+    {
+        await pipePair.GatewayWriter
+            .WriteAsync(CreateGatewayHelloEnvelope(), cancellationToken)
+            .ConfigureAwait(false);
+
+        WorkerEnvelope hello = await pipePair.GatewayReader.ReadAsync(cancellationToken).ConfigureAwait(false);
+        WorkerEnvelope ready = await pipePair.GatewayReader.ReadAsync(cancellationToken).ConfigureAwait(false);
+
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerHello, hello.BodyCase);
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerReady, ready.BodyCase);
+    }
+
+    private static async Task SendShutdownAndWaitAsync(
+        PipePair pipePair,
+        Task runTask,
+        CancellationToken cancellationToken)
+    {
+        await pipePair.GatewayWriter
+            .WriteAsync(CreateShutdownEnvelope(), cancellationToken)
+            .ConfigureAwait(false);
+
+        WorkerEnvelope shutdownAck = await ReadUntilAsync(
+            pipePair.GatewayReader,
+            WorkerEnvelope.BodyOneofCase.WorkerShutdownAck,
+            cancellationToken);
+
+        Assert.Equal(ProtocolStatusCode.Ok, shutdownAck.WorkerShutdownAck.Status.Code);
+        Task completedTask = await Task
+            .WhenAny(runTask, Task.Delay(TimeSpan.FromSeconds(2), cancellationToken))
+            .ConfigureAwait(false);
+
+        Assert.Same(runTask, completedTask);
+        await runTask.ConfigureAwait(false);
+    }
+
+    private static async Task ThrowIfCompletedAsync(Task task)
+    {
+        await Task.Delay(TimeSpan.FromMilliseconds(100));
+        if (task.IsCompleted)
+        {
+            await task;
+        }
+    }
+
+    private static Task<WorkerEnvelope> ReadUntilAsync(
+        WorkerFrameReader reader,
+        WorkerEnvelope.BodyOneofCase expectedBody,
+        CancellationToken cancellationToken)
+    {
+        return ReadUntilAsync(
+            reader,
+            expectedBody,
+            _ => true,
+            cancellationToken);
+    }
+
+    private static async Task<WorkerEnvelope> ReadUntilAsync(
+        WorkerFrameReader reader,
+        WorkerEnvelope.BodyOneofCase expectedBody,
+        Func<WorkerEnvelope, bool> predicate,
+        CancellationToken cancellationToken)
+    {
+        while (true)
+        {
+            WorkerEnvelope envelope = await reader.ReadAsync(cancellationToken).ConfigureAwait(false);
+            if (envelope.BodyCase == expectedBody && predicate(envelope))
+            {
+                return envelope;
+            }
+        }
+    }
+
     private static WorkerEnvelope[] ReadWrittenFrames(
         MemoryStream stream,
         WorkerFrameProtocolOptions options)
@@ -219,4 +473,157 @@ public sealed class WorkerPipeSessionTests
         buffer[2] = (byte)(value >> 16);
         buffer[3] = (byte)(value >> 24);
     }
+
+    private sealed class FakeRuntimeSession : IWorkerRuntimeSession
+    {
+        private readonly ManualResetEventSlim releaseDispatch = new(false);
+        private readonly object gate = new();
+        private WorkerRuntimeHeartbeatSnapshot snapshot = new(
+            DateTimeOffset.UtcNow,
+            pendingCommandCount: 0,
+            outboundEventQueueDepth: 0,
+            lastEventSequence: 0,
+            currentCommandCorrelationId: string.Empty);
+
+        public ManualResetEventSlim DispatchStarted { get; } = new(false);
+
+        public bool BlockDispatch { get; set; }
+
+        public Task<WorkerReady> StartAsync(
+            int workerProcessId,
+            CancellationToken cancellationToken = default)
+        {
+            return Task.FromResult(new WorkerReady
+            {
+                WorkerProcessId = workerProcessId,
+                MxaccessProgid = MxGateway.Worker.MxAccess.MxAccessInteropInfo.ProgId,
+                MxaccessClsid = MxGateway.Worker.MxAccess.MxAccessInteropInfo.Clsid,
+                ReadyTimestamp = Timestamp.FromDateTimeOffset(DateTimeOffset.UtcNow),
+            });
+        }
+
+        public Task<MxCommandReply> DispatchAsync(StaCommand command)
+        {
+            return Task.Run(
+                () =>
+                {
+                    SetSnapshot(new WorkerRuntimeHeartbeatSnapshot(
+                        DateTimeOffset.UtcNow,
+                        pendingCommandCount: 0,
+                        outboundEventQueueDepth: 0,
+                        lastEventSequence: 0,
+                        command.CorrelationId));
+                    DispatchStarted.Set();
+
+                    if (BlockDispatch)
+                    {
+                        releaseDispatch.Wait(TimeSpan.FromSeconds(5));
+                    }
+
+                    SetSnapshot(new WorkerRuntimeHeartbeatSnapshot(
+                        DateTimeOffset.UtcNow,
+                        pendingCommandCount: 0,
+                        outboundEventQueueDepth: 0,
+                        lastEventSequence: 0,
+                        currentCommandCorrelationId: string.Empty));
+
+                    return new MxCommandReply
+                    {
+                        SessionId = command.SessionId,
+                        CorrelationId = command.CorrelationId,
+                        Kind = command.Kind,
+                        ProtocolStatus = new ProtocolStatus
+                        {
+                            Code = ProtocolStatusCode.Ok,
+                            Message = "OK",
+                        },
+                    };
+                });
+        }
+
+        public WorkerRuntimeHeartbeatSnapshot CaptureHeartbeat()
+        {
+            lock (gate)
+            {
+                return snapshot;
+            }
+        }
+
+        public void RequestShutdown()
+        {
+            releaseDispatch.Set();
+        }
+
+        public void ReleaseDispatch()
+        {
+            releaseDispatch.Set();
+        }
+
+        public void SetSnapshot(WorkerRuntimeHeartbeatSnapshot value)
+        {
+            lock (gate)
+            {
+                snapshot = value;
+            }
+        }
+
+        public void Dispose()
+        {
+            releaseDispatch.Set();
+            releaseDispatch.Dispose();
+            DispatchStarted.Dispose();
+        }
+    }
+
+    private sealed class PipePair : IDisposable
+    {
+        private readonly NamedPipeServerStream gatewayStream;
+
+        private PipePair(
+            NamedPipeServerStream gatewayStream,
+            NamedPipeClientStream workerStream)
+        {
+            this.gatewayStream = gatewayStream;
+            WorkerStream = workerStream;
+            WorkerFrameProtocolOptions options = CreateOptions();
+            GatewayReader = new WorkerFrameReader(gatewayStream, options);
+            GatewayWriter = new WorkerFrameWriter(gatewayStream, options);
+        }
+
+        public Stream WorkerStream { get; }
+
+        public WorkerFrameReader GatewayReader { get; }
+
+        public WorkerFrameWriter GatewayWriter { get; }
+
+        public static async Task<PipePair> CreateAsync(CancellationToken cancellationToken)
+        {
+            string pipeName = $"mxaccessgw-worker-session-tests-{Guid.NewGuid():N}";
+            NamedPipeServerStream gatewayStream = new(
+                pipeName,
+                PipeDirection.InOut,
+                maxNumberOfServerInstances: 1,
+                PipeTransmissionMode.Byte,
+                PipeOptions.Asynchronous);
+            NamedPipeClientStream workerStream = new(
+                ".",
+                pipeName,
+                PipeDirection.InOut,
+                PipeOptions.Asynchronous);
+
+            Task waitForConnectionTask = gatewayStream.WaitForConnectionAsync();
+            await Task
+                .Run(() => workerStream.Connect(5000), cancellationToken)
+                .ConfigureAwait(false);
+            await waitForConnectionTask.ConfigureAwait(false);
+
+            return new PipePair(gatewayStream, workerStream);
+        }
+
+        public void Dispose()
+        {
+            WorkerStream.Dispose();
+            gatewayStream.Dispose();
+        }
+    }
 }

src/MxGateway.Worker.Tests/MxAccess/MxAccessCommandExecutorTests.cs

@@ -78,6 +78,166 @@ public sealed class MxAccessCommandExecutorTests
         Assert.Equal(44, registeredServerHandle.ServerHandle);
     }
 
+    [Fact]
+    public async Task DispatchAsync_AddItem_CallsMxAccessOnStaAndTracksItemHandle()
+    {
+        FakeMxAccessComObject fakeComObject = new(
+            registerHandle: 46,
+            addItemHandle: 501);
+        FakeMxAccessComObjectFactory factory = new(fakeComObject);
+        using StaRuntime runtime = CreateRuntime();
+        using MxAccessStaSession session = new(runtime, factory, new NoopEventSink());
+        await session.StartAsync(workerProcessId: 1234);
+        await session.DispatchAsync(CreateRegisterCommand("register-before-add", "client-a"));
+
+        MxCommandReply reply = await session.DispatchAsync(CreateAddItemCommand(
+            "add-item",
+            46,
+            "Galaxy.Tag.Value"));
+
+        Assert.Equal(ProtocolStatusCode.Ok, reply.ProtocolStatus.Code);
+        Assert.True(reply.HasHresult);
+        Assert.Equal(0, reply.Hresult);
+        Assert.Equal(501, reply.AddItem.ItemHandle);
+        Assert.Equal(MxDataType.Integer, reply.ReturnValue.DataType);
+        Assert.Equal(501, reply.ReturnValue.Int32Value);
+        Assert.Equal(46, fakeComObject.AddItemServerHandle);
+        Assert.Equal("Galaxy.Tag.Value", fakeComObject.AddItemDefinition);
+        Assert.Equal(runtime.StaThreadId, fakeComObject.AddItemThreadId);
+
+        RegisteredItemHandle registeredItemHandle = Assert.Single(
+            await session.GetRegisteredItemHandlesAsync());
+        Assert.Equal(46, registeredItemHandle.ServerHandle);
+        Assert.Equal(501, registeredItemHandle.ItemHandle);
+        Assert.Equal("Galaxy.Tag.Value", registeredItemHandle.ItemDefinition);
+        Assert.Equal(string.Empty, registeredItemHandle.ItemContext);
+        Assert.False(registeredItemHandle.HasItemContext);
+    }
+
+    [Fact]
+    public async Task DispatchAsync_AddItem2_PassesContextExactlyAndTracksItemHandle()
+    {
+        FakeMxAccessComObject fakeComObject = new(
+            registerHandle: 47,
+            addItem2Handle: 502);
+        FakeMxAccessComObjectFactory factory = new(fakeComObject);
+        using StaRuntime runtime = CreateRuntime();
+        using MxAccessStaSession session = new(runtime, factory, new NoopEventSink());
+        await session.StartAsync(workerProcessId: 1234);
+        await session.DispatchAsync(CreateRegisterCommand("register-before-add2", "client-a"));
+
+        MxCommandReply reply = await session.DispatchAsync(CreateAddItem2Command(
+            "add-item2",
+            47,
+            "TestInt",
+            "TestChildObject"));
+
+        Assert.Equal(ProtocolStatusCode.Ok, reply.ProtocolStatus.Code);
+        Assert.Equal(502, reply.AddItem2.ItemHandle);
+        Assert.Equal(MxDataType.Integer, reply.ReturnValue.DataType);
+        Assert.Equal(502, reply.ReturnValue.Int32Value);
+        Assert.Equal(47, fakeComObject.AddItem2ServerHandle);
+        Assert.Equal("TestInt", fakeComObject.AddItem2Definition);
+        Assert.Equal("TestChildObject", fakeComObject.AddItem2Context);
+        Assert.Equal(runtime.StaThreadId, fakeComObject.AddItem2ThreadId);
+
+        RegisteredItemHandle registeredItemHandle = Assert.Single(
+            await session.GetRegisteredItemHandlesAsync());
+        Assert.Equal(47, registeredItemHandle.ServerHandle);
+        Assert.Equal(502, registeredItemHandle.ItemHandle);
+        Assert.Equal("TestInt", registeredItemHandle.ItemDefinition);
+        Assert.Equal("TestChildObject", registeredItemHandle.ItemContext);
+        Assert.True(registeredItemHandle.HasItemContext);
+    }
+
+    [Fact]
+    public async Task DispatchAsync_RemoveItem_CallsMxAccessOnStaAndRemovesTrackedItemHandle()
+    {
+        FakeMxAccessComObject fakeComObject = new(
+            registerHandle: 48,
+            addItemHandle: 503);
+        FakeMxAccessComObjectFactory factory = new(fakeComObject);
+        using StaRuntime runtime = CreateRuntime();
+        using MxAccessStaSession session = new(runtime, factory, new NoopEventSink());
+        await session.StartAsync(workerProcessId: 1234);
+        await session.DispatchAsync(CreateRegisterCommand("register-before-remove", "client-a"));
+        await session.DispatchAsync(CreateAddItemCommand("add-before-remove", 48, "Galaxy.Tag.Value"));
+
+        MxCommandReply reply = await session.DispatchAsync(CreateRemoveItemCommand(
+            "remove-item",
+            48,
+            503));
+
+        Assert.Equal(ProtocolStatusCode.Ok, reply.ProtocolStatus.Code);
+        Assert.True(reply.HasHresult);
+        Assert.Equal(0, reply.Hresult);
+        Assert.Equal(48, fakeComObject.RemoveItemServerHandle);
+        Assert.Equal(503, fakeComObject.RemovedItemHandle);
+        Assert.Equal(runtime.StaThreadId, fakeComObject.RemoveItemThreadId);
+        Assert.Empty(await session.GetRegisteredItemHandlesAsync());
+    }
+
+    [Fact]
+    public async Task DispatchAsync_RemoveItemWithCrossServerHandle_PreservesHResultAndKeepsTrackedItemHandle()
+    {
+        const int hresult = unchecked((int)0x80070057);
+        FakeMxAccessComObject fakeComObject = new(
+            registerHandle: 49,
+            addItemHandle: 504,
+            removeItemException: new COMException("Invalid item handle.", hresult));
+        FakeMxAccessComObjectFactory factory = new(fakeComObject);
+        using StaRuntime runtime = CreateRuntime();
+        using MxAccessStaSession session = new(runtime, factory, new NoopEventSink());
+        await session.StartAsync(workerProcessId: 1234);
+        await session.DispatchAsync(CreateRegisterCommand("register-before-remove-failure", "client-a"));
+        await session.DispatchAsync(CreateAddItemCommand("add-before-remove-failure", 49, "Galaxy.Tag.Value"));
+
+        MxCommandReply reply = await session.DispatchAsync(CreateRemoveItemCommand(
+            "remove-item-failure",
+            999,
+            504));
+
+        Assert.Equal(ProtocolStatusCode.MxaccessFailure, reply.ProtocolStatus.Code);
+        Assert.True(reply.HasHresult);
+        Assert.Equal(hresult, reply.Hresult);
+        Assert.Contains("0x80070057", reply.DiagnosticMessage);
+        Assert.Equal(999, fakeComObject.RemoveItemServerHandle);
+        Assert.Equal(504, fakeComObject.RemovedItemHandle);
+
+        RegisteredItemHandle registeredItemHandle = Assert.Single(
+            await session.GetRegisteredItemHandlesAsync());
+        Assert.Equal(49, registeredItemHandle.ServerHandle);
+        Assert.Equal(504, registeredItemHandle.ItemHandle);
+    }
+
+    [Fact]
+    public async Task DispatchAsync_AddItem2WhenMxAccessThrows_PreservesHResultAndDoesNotTrackItemHandle()
+    {
+        const int hresult = unchecked((int)0x80070057);
+        FakeMxAccessComObject fakeComObject = new(
+            registerHandle: 50,
+            addItem2Exception: new COMException("Invalid server handle.", hresult));
+        FakeMxAccessComObjectFactory factory = new(fakeComObject);
+        using StaRuntime runtime = CreateRuntime();
+        using MxAccessStaSession session = new(runtime, factory, new NoopEventSink());
+        await session.StartAsync(workerProcessId: 1234);
+
+        MxCommandReply reply = await session.DispatchAsync(CreateAddItem2Command(
+            "add-item2-failure",
+            9001,
+            "TestInt",
+            "TestChildObject"));
+
+        Assert.Equal(ProtocolStatusCode.MxaccessFailure, reply.ProtocolStatus.Code);
+        Assert.True(reply.HasHresult);
+        Assert.Equal(hresult, reply.Hresult);
+        Assert.Contains("0x80070057", reply.DiagnosticMessage);
+        Assert.Equal(9001, fakeComObject.AddItem2ServerHandle);
+        Assert.Equal("TestInt", fakeComObject.AddItem2Definition);
+        Assert.Equal("TestChildObject", fakeComObject.AddItem2Context);
+        Assert.Empty(await session.GetRegisteredItemHandlesAsync());
+    }
+
     [Fact]
     public async Task DispatchAsync_RegisterWithoutPayload_ReturnsInvalidRequest()
     {
@@ -98,6 +258,26 @@ public sealed class MxAccessCommandExecutorTests
         Assert.Null(factory.FakeComObject.RegisteredClientName);
     }
 
+    [Fact]
+    public async Task DispatchAsync_AddItemWithoutPayload_ReturnsInvalidRequest()
+    {
+        FakeMxAccessComObjectFactory factory = new(new FakeMxAccessComObject(registerHandle: 51));
+        using StaRuntime runtime = CreateRuntime();
+        using MxAccessStaSession session = new(runtime, factory, new NoopEventSink());
+        await session.StartAsync(workerProcessId: 1234);
+
+        MxCommandReply reply = await session.DispatchAsync(new StaCommand(
+            "session-1",
+            "missing-add-payload",
+            new MxCommand
+            {
+                Kind = MxCommandKind.AddItem,
+            }));
+
+        Assert.Equal(ProtocolStatusCode.InvalidRequest, reply.ProtocolStatus.Code);
+        Assert.Null(factory.FakeComObject.AddItemDefinition);
+    }
+
     private static StaCommand CreateRegisterCommand(
         string correlationId,
         string clientName)
@@ -132,6 +312,65 @@ public sealed class MxAccessCommandExecutorTests
             });
     }
 
+    private static StaCommand CreateAddItemCommand(
+        string correlationId,
+        int serverHandle,
+        string itemDefinition)
+    {
+        return new StaCommand(
+            "session-1",
+            correlationId,
+            new MxCommand
+            {
+                Kind = MxCommandKind.AddItem,
+                AddItem = new AddItemCommand
+                {
+                    ServerHandle = serverHandle,
+                    ItemDefinition = itemDefinition,
+                },
+            });
+    }
+
+    private static StaCommand CreateAddItem2Command(
+        string correlationId,
+        int serverHandle,
+        string itemDefinition,
+        string itemContext)
+    {
+        return new StaCommand(
+            "session-1",
+            correlationId,
+            new MxCommand
+            {
+                Kind = MxCommandKind.AddItem2,
+                AddItem2 = new AddItem2Command
+                {
+                    ServerHandle = serverHandle,
+                    ItemDefinition = itemDefinition,
+                    ItemContext = itemContext,
+                },
+            });
+    }
+
+    private static StaCommand CreateRemoveItemCommand(
+        string correlationId,
+        int serverHandle,
+        int itemHandle)
+    {
+        return new StaCommand(
+            "session-1",
+            correlationId,
+            new MxCommand
+            {
+                Kind = MxCommandKind.RemoveItem,
+                RemoveItem = new RemoveItemCommand
+                {
+                    ServerHandle = serverHandle,
+                    ItemHandle = itemHandle,
+                },
+            });
+    }
+
     private static StaRuntime CreateRuntime()
     {
         return new StaRuntime(
@@ -143,14 +382,29 @@ public sealed class MxAccessCommandExecutorTests
     private sealed class FakeMxAccessComObject
     {
         private readonly int registerHandle;
+        private readonly int addItemHandle;
+        private readonly int addItem2Handle;
         private readonly Exception? unregisterException;
+        private readonly Exception? addItemException;
+        private readonly Exception? addItem2Exception;
+        private readonly Exception? removeItemException;
 
         public FakeMxAccessComObject(
             int registerHandle,
-            Exception? unregisterException = null)
+            int addItemHandle = 0,
+            int addItem2Handle = 0,
+            Exception? unregisterException = null,
+            Exception? addItemException = null,
+            Exception? addItem2Exception = null,
+            Exception? removeItemException = null)
         {
             this.registerHandle = registerHandle;
+            this.addItemHandle = addItemHandle;
+            this.addItem2Handle = addItem2Handle;
             this.unregisterException = unregisterException;
+            this.addItemException = addItemException;
+            this.addItem2Exception = addItem2Exception;
+            this.removeItemException = removeItemException;
         }
 
         public string? RegisteredClientName { get; private set; }
@@ -161,6 +415,26 @@ public sealed class MxAccessCommandExecutorTests
 
         public int? UnregisterThreadId { get; private set; }
 
+        public int? AddItemServerHandle { get; private set; }
+
+        public string? AddItemDefinition { get; private set; }
+
+        public int? AddItemThreadId { get; private set; }
+
+        public int? AddItem2ServerHandle { get; private set; }
+
+        public string? AddItem2Definition { get; private set; }
+
+        public string? AddItem2Context { get; private set; }
+
+        public int? AddItem2ThreadId { get; private set; }
+
+        public int? RemoveItemServerHandle { get; private set; }
+
+        public int? RemovedItemHandle { get; private set; }
+
+        public int? RemoveItemThreadId { get; private set; }
+
         public int Register(string clientName)
         {
             RegisteredClientName = clientName;
@@ -179,6 +453,54 @@ public sealed class MxAccessCommandExecutorTests
                 throw unregisterException;
             }
         }
+
+        public int AddItem(
+            int serverHandle,
+            string itemDefinition)
+        {
+            AddItemServerHandle = serverHandle;
+            AddItemDefinition = itemDefinition;
+            AddItemThreadId = Environment.CurrentManagedThreadId;
+
+            if (addItemException is not null)
+            {
+                throw addItemException;
+            }
+
+            return addItemHandle;
+        }
+
+        public int AddItem2(
+            int serverHandle,
+            string itemDefinition,
+            string itemContext)
+        {
+            AddItem2ServerHandle = serverHandle;
+            AddItem2Definition = itemDefinition;
+            AddItem2Context = itemContext;
+            AddItem2ThreadId = Environment.CurrentManagedThreadId;
+
+            if (addItem2Exception is not null)
+            {
+                throw addItem2Exception;
+            }
+
+            return addItem2Handle;
+        }
+
+        public void RemoveItem(
+            int serverHandle,
+            int itemHandle)
+        {
+            RemoveItemServerHandle = serverHandle;
+            RemovedItemHandle = itemHandle;
+            RemoveItemThreadId = Environment.CurrentManagedThreadId;
+
+            if (removeItemException is not null)
+            {
+                throw removeItemException;
+            }
+        }
     }
 
     private sealed class FakeMxAccessComObjectFactory : IMxAccessComObjectFactory

src/MxGateway.Worker.Tests/MxAccess/MxAccessLiveComCreationTests.cs

@@ -8,6 +8,11 @@ namespace MxGateway.Worker.Tests.MxAccess;
 
 public sealed class MxAccessLiveComCreationTests
 {
+    private const string LiveClientName = "MxGateway.Worker.Tests";
+    private const string DefaultLiveAddItemReference = "TestChildObject.TestInt";
+    private const string DefaultLiveAddItem2Definition = "TestInt";
+    private const string DefaultLiveAddItem2Context = "TestChildObject";
+
     [Fact]
     public async Task StartAsync_WhenOptedIn_CreatesInstalledMxAccessComObjectOnSta()
     {
@@ -43,7 +48,7 @@ public sealed class MxAccessLiveComCreationTests
                 Kind = MxCommandKind.Register,
                 Register = new RegisterCommand
                 {
-                    ClientName = "MxGateway.Worker.Tests",
+                    ClientName = LiveClientName,
                 },
             }));
 
@@ -65,6 +70,151 @@ public sealed class MxAccessLiveComCreationTests
         Assert.Equal(ProtocolStatusCode.Ok, unregisterReply.ProtocolStatus.Code);
     }
 
+    [Fact]
+    public async Task AddItemAndRemoveItem_WhenOptedIn_RoundTripsInstalledMxAccessItemHandle()
+    {
+        if (!RunLiveMxAccessTests())
+        {
+            return;
+        }
+
+        using MxAccessStaSession session = new();
+        await session.StartAsync(workerProcessId: 1234);
+
+        MxCommandReply registerReply = await RegisterLiveSessionAsync(session, "live-add-register");
+        int serverHandle = registerReply.Register.ServerHandle;
+        int itemHandle = 0;
+
+        try
+        {
+            MxCommandReply addItemReply = await session.DispatchAsync(new StaCommand(
+                "session-1",
+                "live-add-item",
+                new MxCommand
+                {
+                    Kind = MxCommandKind.AddItem,
+                    AddItem = new AddItemCommand
+                    {
+                        ServerHandle = serverHandle,
+                        ItemDefinition = GetLiveAddItemReference(),
+                    },
+                }));
+
+            Assert.Equal(ProtocolStatusCode.Ok, addItemReply.ProtocolStatus.Code);
+            Assert.True(addItemReply.AddItem.ItemHandle > 0);
+            itemHandle = addItemReply.AddItem.ItemHandle;
+
+            MxCommandReply removeItemReply = await session.DispatchAsync(new StaCommand(
+                "session-1",
+                "live-remove-item",
+                new MxCommand
+                {
+                    Kind = MxCommandKind.RemoveItem,
+                    RemoveItem = new RemoveItemCommand
+                    {
+                        ServerHandle = serverHandle,
+                        ItemHandle = itemHandle,
+                    },
+                }));
+
+            Assert.Equal(ProtocolStatusCode.Ok, removeItemReply.ProtocolStatus.Code);
+            itemHandle = 0;
+        }
+        finally
+        {
+            if (itemHandle > 0)
+            {
+                await session.DispatchAsync(new StaCommand(
+                    "session-1",
+                    "live-remove-item-cleanup",
+                    new MxCommand
+                    {
+                        Kind = MxCommandKind.RemoveItem,
+                        RemoveItem = new RemoveItemCommand
+                        {
+                            ServerHandle = serverHandle,
+                            ItemHandle = itemHandle,
+                        },
+                    }));
+            }
+
+            await UnregisterLiveSessionAsync(session, serverHandle, "live-add-unregister");
+        }
+    }
+
+    [Fact]
+    public async Task AddItem2AndRemoveItem_WhenOptedIn_PreservesContextForInstalledMxAccess()
+    {
+        if (!RunLiveMxAccessTests())
+        {
+            return;
+        }
+
+        using MxAccessStaSession session = new();
+        await session.StartAsync(workerProcessId: 1234);
+
+        MxCommandReply registerReply = await RegisterLiveSessionAsync(session, "live-add2-register");
+        int serverHandle = registerReply.Register.ServerHandle;
+        int itemHandle = 0;
+
+        try
+        {
+            MxCommandReply addItem2Reply = await session.DispatchAsync(new StaCommand(
+                "session-1",
+                "live-add-item2",
+                new MxCommand
+                {
+                    Kind = MxCommandKind.AddItem2,
+                    AddItem2 = new AddItem2Command
+                    {
+                        ServerHandle = serverHandle,
+                        ItemDefinition = DefaultLiveAddItem2Definition,
+                        ItemContext = DefaultLiveAddItem2Context,
+                    },
+                }));
+
+            Assert.Equal(ProtocolStatusCode.Ok, addItem2Reply.ProtocolStatus.Code);
+            Assert.True(addItem2Reply.AddItem2.ItemHandle > 0);
+            itemHandle = addItem2Reply.AddItem2.ItemHandle;
+
+            MxCommandReply removeItemReply = await session.DispatchAsync(new StaCommand(
+                "session-1",
+                "live-remove-item2",
+                new MxCommand
+                {
+                    Kind = MxCommandKind.RemoveItem,
+                    RemoveItem = new RemoveItemCommand
+                    {
+                        ServerHandle = serverHandle,
+                        ItemHandle = itemHandle,
+                    },
+                }));
+
+            Assert.Equal(ProtocolStatusCode.Ok, removeItemReply.ProtocolStatus.Code);
+            itemHandle = 0;
+        }
+        finally
+        {
+            if (itemHandle > 0)
+            {
+                await session.DispatchAsync(new StaCommand(
+                    "session-1",
+                    "live-remove-item2-cleanup",
+                    new MxCommand
+                    {
+                        Kind = MxCommandKind.RemoveItem,
+                        RemoveItem = new RemoveItemCommand
+                        {
+                            ServerHandle = serverHandle,
+                            ItemHandle = itemHandle,
+                        },
+                    }));
+            }
+
+            await UnregisterLiveSessionAsync(session, serverHandle, "live-add2-unregister");
+        }
+    }
+
     private static bool RunLiveMxAccessTests()
     {
         return string.Equals(
@@ -72,4 +222,55 @@ public sealed class MxAccessLiveComCreationTests
             "1",
             StringComparison.Ordinal);
     }
+
+    private static string GetLiveAddItemReference()
+    {
+        string itemReference = Environment.GetEnvironmentVariable("MXGATEWAY_LIVE_MXACCESS_ITEM");
+
+        return string.IsNullOrWhiteSpace(itemReference)
+            ? DefaultLiveAddItemReference
+            : itemReference;
+    }
+
+    private static async Task<MxCommandReply> RegisterLiveSessionAsync(
+        MxAccessStaSession session,
+        string correlationId)
+    {
+        MxCommandReply reply = await session.DispatchAsync(new StaCommand(
+            "session-1",
+            correlationId,
+            new MxCommand
+            {
+                Kind = MxCommandKind.Register,
+                Register = new RegisterCommand
+                {
+                    ClientName = LiveClientName,
+                },
+            }));
+
+        Assert.Equal(ProtocolStatusCode.Ok, reply.ProtocolStatus.Code);
+        Assert.True(reply.Register.ServerHandle > 0);
+
+        return reply;
+    }
+
+    private static async Task UnregisterLiveSessionAsync(
+        MxAccessStaSession session,
+        int serverHandle,
+        string correlationId)
+    {
+        MxCommandReply unregisterReply = await session.DispatchAsync(new StaCommand(
+            "session-1",
+            correlationId,
+            new MxCommand
+            {
+                Kind = MxCommandKind.Unregister,
+                Unregister = new UnregisterCommand
+                {
+                    ServerHandle = serverHandle,
+                },
+            }));
+
+        Assert.Equal(ProtocolStatusCode.Ok, unregisterReply.ProtocolStatus.Code);
+    }
 }

src/MxGateway.Worker/Ipc/WorkerPipeClient.cs

@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 using System.IO.Pipes;
 using System.Threading;
 using System.Threading.Tasks;
@@ -11,6 +12,7 @@ public sealed class WorkerPipeClient : IWorkerPipeClient
     public const int DefaultConnectTimeoutMilliseconds = 30000;
 
     private readonly int _connectTimeoutMilliseconds;
+    private readonly Func<Stream, WorkerFrameProtocolOptions, WorkerPipeSession> _sessionFactory;
 
     public WorkerPipeClient()
         : this(DefaultConnectTimeoutMilliseconds)
@@ -18,6 +20,15 @@ public sealed class WorkerPipeClient : IWorkerPipeClient
     }
 
     public WorkerPipeClient(int connectTimeoutMilliseconds)
+        : this(
+            connectTimeoutMilliseconds,
+            (stream, frameOptions) => new WorkerPipeSession(stream, frameOptions))
+    {
+    }
+
+    public WorkerPipeClient(
+        int connectTimeoutMilliseconds,
+        Func<Stream, WorkerFrameProtocolOptions, WorkerPipeSession> sessionFactory)
     {
         if (connectTimeoutMilliseconds <= 0)
         {
@@ -26,6 +37,7 @@ public sealed class WorkerPipeClient : IWorkerPipeClient
                 "Worker pipe connect timeout must be greater than zero.");
         }
 
+        _sessionFactory = sessionFactory ?? throw new ArgumentNullException(nameof(sessionFactory));
         _connectTimeoutMilliseconds = connectTimeoutMilliseconds;
     }
 
@@ -48,8 +60,8 @@ public sealed class WorkerPipeClient : IWorkerPipeClient
 
         await ConnectAsync(pipe, cancellationToken).ConfigureAwait(false);
 
-        WorkerPipeSession session = new(pipe, frameOptions);
+        WorkerPipeSession session = _sessionFactory(pipe, frameOptions);
-        await session.CompleteStartupHandshakeAsync(cancellationToken).ConfigureAwait(false);
+        await session.RunAsync(cancellationToken).ConfigureAwait(false);
     }
 
     private Task ConnectAsync(

src/MxGateway.Worker/Ipc/WorkerPipeSession.cs

@@ -6,6 +6,7 @@ using System.Threading.Tasks;
 using Google.Protobuf.WellKnownTypes;
 using MxGateway.Contracts.Proto;
 using MxGateway.Worker.MxAccess;
+using MxGateway.Worker.Sta;
 
 namespace MxGateway.Worker.Ipc;
 
@@ -13,10 +14,14 @@ public sealed class WorkerPipeSession
 {
     private readonly WorkerFrameProtocolOptions _options;
     private readonly Func<int> _processIdProvider;
+    private readonly Func<IWorkerRuntimeSession> _runtimeSessionFactory;
+    private readonly WorkerPipeSessionOptions _sessionOptions;
     private readonly WorkerFrameReader _reader;
     private readonly WorkerFrameWriter _writer;
-    private MxAccessStaSession? _mxAccessStaSession;
+    private IWorkerRuntimeSession? _runtimeSession;
     private long _nextSequence;
+    private WorkerState _state = WorkerState.Starting;
+    private bool _watchdogFaultSent;
 
     public WorkerPipeSession(
         Stream stream,
@@ -34,11 +39,49 @@ public sealed class WorkerPipeSession
         WorkerFrameWriter writer,
         WorkerFrameProtocolOptions options,
         Func<int> processIdProvider)
+        : this(
+            reader,
+            writer,
+            options,
+            processIdProvider,
+            new WorkerPipeSessionOptions(),
+            () => new MxAccessStaSession())
+    {
+    }
+
+    public WorkerPipeSession(
+        WorkerFrameReader reader,
+        WorkerFrameWriter writer,
+        WorkerFrameProtocolOptions options,
+        Func<int> processIdProvider,
+        WorkerPipeSessionOptions sessionOptions,
+        Func<IWorkerRuntimeSession> runtimeSessionFactory)
     {
         _reader = reader ?? throw new ArgumentNullException(nameof(reader));
         _writer = writer ?? throw new ArgumentNullException(nameof(writer));
         _options = options ?? throw new ArgumentNullException(nameof(options));
         _processIdProvider = processIdProvider ?? throw new ArgumentNullException(nameof(processIdProvider));
+        _sessionOptions = sessionOptions ?? throw new ArgumentNullException(nameof(sessionOptions));
+        _runtimeSessionFactory = runtimeSessionFactory ?? throw new ArgumentNullException(nameof(runtimeSessionFactory));
+        _sessionOptions.Validate();
+    }
+
+    public async Task RunAsync(CancellationToken cancellationToken = default)
+    {
+        _runtimeSession = _runtimeSessionFactory();
+        try
+        {
+            await CompleteStartupHandshakeAsync(
+                token => _runtimeSession.StartAsync(_processIdProvider(), token),
+                cancellationToken).ConfigureAwait(false);
+            await RunMessageLoopAsync(cancellationToken).ConfigureAwait(false);
+        }
+        finally
+        {
+            _runtimeSession?.Dispose();
+            _runtimeSession = null;
+            _state = WorkerState.Stopped;
+        }
     }
 
     public Task CompleteStartupHandshakeAsync(CancellationToken cancellationToken = default)
@@ -76,11 +119,14 @@ public sealed class WorkerPipeSession
         try
         {
             WorkerEnvelope envelope = await _reader.ReadAsync(cancellationToken).ConfigureAwait(false);
+            _state = WorkerState.Handshaking;
             ValidateGatewayHello(envelope);
 
             await WriteWorkerHelloAsync(cancellationToken).ConfigureAwait(false);
+            _state = WorkerState.InitializingSta;
             WorkerReady ready = await initializeMxAccessAsync(cancellationToken).ConfigureAwait(false);
             await WriteWorkerReadyAsync(ready, cancellationToken).ConfigureAwait(false);
+            _state = WorkerState.Ready;
         }
         catch (WorkerFrameProtocolException exception)
         {
@@ -140,6 +186,174 @@ public sealed class WorkerPipeSession
         return _writer.WriteAsync(CreateEnvelope(ready), cancellationToken);
     }
 
+    private async Task RunMessageLoopAsync(CancellationToken cancellationToken)
+    {
+        using CancellationTokenSource heartbeatCancellation = CancellationTokenSource
+            .CreateLinkedTokenSource(cancellationToken);
+        Task heartbeatTask = RunHeartbeatLoopAsync(heartbeatCancellation.Token);
+
+        try
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                Task<WorkerEnvelope> readTask = _reader.ReadAsync(cancellationToken);
+                Task completedTask = await Task.WhenAny(readTask, heartbeatTask).ConfigureAwait(false);
+                if (completedTask == heartbeatTask)
+                {
+                    await heartbeatTask.ConfigureAwait(false);
+                }
+
+                WorkerEnvelope envelope = await readTask.ConfigureAwait(false);
+                bool keepReading = await DispatchGatewayEnvelopeAsync(envelope, cancellationToken).ConfigureAwait(false);
+                if (!keepReading)
+                {
+                    return;
+                }
+            }
+        }
+        finally
+        {
+            heartbeatCancellation.Cancel();
+            try
+            {
+                await heartbeatTask.ConfigureAwait(false);
+            }
+            catch (OperationCanceledException)
+            {
+            }
+        }
+    }
+
+    private async Task<bool> DispatchGatewayEnvelopeAsync(
+        WorkerEnvelope envelope,
+        CancellationToken cancellationToken)
+    {
+        switch (envelope.BodyCase)
+        {
+            case WorkerEnvelope.BodyOneofCase.WorkerCommand:
+                _ = ProcessCommandAsync(envelope, cancellationToken);
+                return true;
+            case WorkerEnvelope.BodyOneofCase.WorkerShutdown:
+                await ShutdownAsync(envelope.WorkerShutdown, cancellationToken).ConfigureAwait(false);
+                return false;
+            case WorkerEnvelope.BodyOneofCase.WorkerCancel:
+                return true;
+            default:
+                throw new WorkerFrameProtocolException(
+                    WorkerFrameProtocolErrorCode.UnexpectedEnvelopeBody,
+                    $"Worker received unexpected gateway envelope body {envelope.BodyCase}.");
+        }
+    }
+
+    private async Task ProcessCommandAsync(
+        WorkerEnvelope envelope,
+        CancellationToken cancellationToken)
+    {
+        IWorkerRuntimeSession runtimeSession = _runtimeSession
+            ?? throw new InvalidOperationException("Worker runtime session has not been initialized.");
+        WorkerCommand workerCommand = envelope.WorkerCommand;
+        MxCommand command = workerCommand.Command;
+        StaCommand staCommand = new(
+            _options.SessionId,
+            envelope.CorrelationId,
+            command,
+            workerCommand.EnqueueTimestamp,
+            cancellationToken);
+
+        try
+        {
+            MxCommandReply reply = await runtimeSession.DispatchAsync(staCommand).ConfigureAwait(false);
+            await _writer
+                .WriteAsync(
+                    CreateEnvelope(new WorkerCommandReply
+                    {
+                        Reply = reply,
+                        CompletedTimestamp = Timestamp.FromDateTime(DateTime.UtcNow),
+                    }),
+                    cancellationToken)
+                .ConfigureAwait(false);
+        }
+        catch (Exception exception) when (exception is not OperationCanceledException)
+        {
+            _state = WorkerState.Faulted;
+            await TryWriteFaultAsync(
+                CreateFault(
+                    WorkerFaultCategory.MxaccessCommandFailed,
+                    staCommand.MethodName,
+                    exception),
+                cancellationToken).ConfigureAwait(false);
+        }
+    }
+
+    private async Task ShutdownAsync(
+        WorkerShutdown shutdown,
+        CancellationToken cancellationToken)
+    {
+        _state = WorkerState.ShuttingDown;
+        _runtimeSession?.RequestShutdown();
+
+        await _writer
+            .WriteAsync(
+                CreateEnvelope(
+                    new WorkerShutdownAck
+                    {
+                        Status = new ProtocolStatus
+                        {
+                            Code = ProtocolStatusCode.Ok,
+                            Message = string.IsNullOrWhiteSpace(shutdown.Reason)
+                                ? "Worker shutdown accepted."
+                                : $"Worker shutdown accepted: {shutdown.Reason}",
+                        },
+                    }),
+                cancellationToken)
+            .ConfigureAwait(false);
+    }
+
+    private async Task RunHeartbeatLoopAsync(CancellationToken cancellationToken)
+    {
+        while (!cancellationToken.IsCancellationRequested)
+        {
+            await Task.Delay(_sessionOptions.HeartbeatInterval, cancellationToken).ConfigureAwait(false);
+            IWorkerRuntimeSession? runtimeSession = _runtimeSession;
+            if (runtimeSession is null)
+            {
+                continue;
+            }
+
+            WorkerRuntimeHeartbeatSnapshot snapshot = runtimeSession.CaptureHeartbeat();
+            await _writer
+                .WriteAsync(CreateEnvelope(CreateHeartbeat(snapshot)), cancellationToken)
+                .ConfigureAwait(false);
+
+            await ReportWatchdogFaultIfNeededAsync(snapshot, cancellationToken).ConfigureAwait(false);
+        }
+    }
+
+    private async Task ReportWatchdogFaultIfNeededAsync(
+        WorkerRuntimeHeartbeatSnapshot snapshot,
+        CancellationToken cancellationToken)
+    {
+        TimeSpan staleFor = DateTimeOffset.UtcNow - snapshot.LastStaActivityUtc;
+        if (staleFor <= _sessionOptions.HeartbeatGrace)
+        {
+            _watchdogFaultSent = false;
+            return;
+        }
+
+        if (_watchdogFaultSent)
+        {
+            return;
+        }
+
+        _watchdogFaultSent = true;
+        await TryWriteFaultAsync(
+            CreateFault(
+                WorkerFaultCategory.StaHung,
+                snapshot.CurrentCommandCorrelationId,
+                $"STA activity is stale by {staleFor}."),
+            cancellationToken).ConfigureAwait(false);
+    }
+
     private async Task TryWriteFaultAsync(
         WorkerFrameProtocolException exception,
         CancellationToken cancellationToken)
@@ -178,6 +392,25 @@ public sealed class WorkerPipeSession
         }
     }
 
+    private async Task TryWriteFaultAsync(
+        WorkerFault fault,
+        CancellationToken cancellationToken)
+    {
+        try
+        {
+            await _writer
+                .WriteAsync(CreateEnvelope(fault), cancellationToken)
+                .ConfigureAwait(false);
+        }
+        catch (Exception faultWriteException) when (
+            faultWriteException is IOException
+            || faultWriteException is ObjectDisposedException
+            || faultWriteException is WorkerFrameProtocolException)
+        {
+            // The runtime fault remains observable through worker exit or pipe closure.
+        }
+    }
+
     private WorkerEnvelope CreateEnvelope(WorkerHello hello)
     {
         return CreateBaseEnvelope(hello);
@@ -193,6 +426,21 @@ public sealed class WorkerPipeSession
         return CreateBaseEnvelope(fault);
     }
 
+    private WorkerEnvelope CreateEnvelope(WorkerCommandReply reply)
+    {
+        return CreateBaseEnvelope(reply);
+    }
+
+    private WorkerEnvelope CreateEnvelope(WorkerShutdownAck shutdownAck)
+    {
+        return CreateBaseEnvelope(shutdownAck);
+    }
+
+    private WorkerEnvelope CreateEnvelope(WorkerHeartbeat heartbeat)
+    {
+        return CreateBaseEnvelope(heartbeat);
+    }
+
     private WorkerEnvelope CreateBaseEnvelope(WorkerHello body)
     {
         WorkerEnvelope envelope = CreateBaseEnvelope();
@@ -214,6 +462,28 @@ public sealed class WorkerPipeSession
         return envelope;
     }
 
+    private WorkerEnvelope CreateBaseEnvelope(WorkerCommandReply body)
+    {
+        WorkerEnvelope envelope = CreateBaseEnvelope();
+        envelope.CorrelationId = body.Reply?.CorrelationId ?? string.Empty;
+        envelope.WorkerCommandReply = body;
+        return envelope;
+    }
+
+    private WorkerEnvelope CreateBaseEnvelope(WorkerShutdownAck body)
+    {
+        WorkerEnvelope envelope = CreateBaseEnvelope();
+        envelope.WorkerShutdownAck = body;
+        return envelope;
+    }
+
+    private WorkerEnvelope CreateBaseEnvelope(WorkerHeartbeat body)
+    {
+        WorkerEnvelope envelope = CreateBaseEnvelope();
+        envelope.WorkerHeartbeat = body;
+        return envelope;
+    }
+
     private WorkerEnvelope CreateBaseEnvelope()
     {
         return new WorkerEnvelope
@@ -231,21 +501,39 @@ public sealed class WorkerPipeSession
 
     private async Task<WorkerReady> InitializeMxAccessAsync(CancellationToken cancellationToken)
     {
-        _mxAccessStaSession = new MxAccessStaSession();
+        _runtimeSession = new MxAccessStaSession();
         try
         {
-            return await _mxAccessStaSession
+            return await _runtimeSession
                 .StartAsync(_processIdProvider(), cancellationToken)
                 .ConfigureAwait(false);
         }
         catch
         {
-            _mxAccessStaSession.Dispose();
+            _runtimeSession.Dispose();
-            _mxAccessStaSession = null;
+            _runtimeSession = null;
             throw;
         }
     }
 
+    private WorkerHeartbeat CreateHeartbeat(WorkerRuntimeHeartbeatSnapshot snapshot)
+    {
+        WorkerState state = string.IsNullOrWhiteSpace(snapshot.CurrentCommandCorrelationId)
+            ? _state
+            : WorkerState.ExecutingCommand;
+
+        return new WorkerHeartbeat
+        {
+            WorkerProcessId = _processIdProvider(),
+            State = state,
+            LastStaActivityTimestamp = Timestamp.FromDateTimeOffset(snapshot.LastStaActivityUtc),
+            PendingCommandCount = snapshot.PendingCommandCount,
+            OutboundEventQueueDepth = snapshot.OutboundEventQueueDepth,
+            LastEventSequence = snapshot.LastEventSequence,
+            CurrentCommandCorrelationId = snapshot.CurrentCommandCorrelationId,
+        };
+    }
+
     private WorkerReady CreateWorkerReady()
     {
         return new WorkerReady
@@ -295,6 +583,42 @@ public sealed class WorkerPipeSession
         return fault;
     }
 
+    private static WorkerFault CreateFault(
+        WorkerFaultCategory category,
+        string commandMethod,
+        Exception exception)
+    {
+        WorkerFault fault = CreateFault(
+            category,
+            commandMethod,
+            exception.Message);
+        fault.ExceptionType = exception.GetType().FullName ?? string.Empty;
+        fault.ProtocolStatus = new ProtocolStatus
+        {
+            Code = ProtocolStatusCode.WorkerUnavailable,
+            Message = exception.Message,
+        };
+        return fault;
+    }
+
+    private static WorkerFault CreateFault(
+        WorkerFaultCategory category,
+        string commandMethod,
+        string diagnosticMessage)
+    {
+        return new WorkerFault
+        {
+            Category = category,
+            CommandMethod = commandMethod ?? string.Empty,
+            DiagnosticMessage = diagnosticMessage,
+            ProtocolStatus = new ProtocolStatus
+            {
+                Code = ProtocolStatusCode.WorkerUnavailable,
+                Message = diagnosticMessage,
+            },
+        };
+    }
+
     private static WorkerFaultCategory MapFaultCategory(WorkerFrameProtocolErrorCode errorCode)
     {
         return errorCode switch

src/MxGateway.Worker/Ipc/WorkerPipeSessionOptions.cs

@@ -0,0 +1,36 @@
+using System;
+
+namespace MxGateway.Worker.Ipc;
+
+public sealed class WorkerPipeSessionOptions
+{
+    public static readonly TimeSpan DefaultHeartbeatInterval = TimeSpan.FromSeconds(5);
+    public static readonly TimeSpan DefaultHeartbeatGrace = TimeSpan.FromSeconds(15);
+
+    public WorkerPipeSessionOptions()
+    {
+        HeartbeatInterval = DefaultHeartbeatInterval;
+        HeartbeatGrace = DefaultHeartbeatGrace;
+    }
+
+    public TimeSpan HeartbeatInterval { get; set; }
+
+    public TimeSpan HeartbeatGrace { get; set; }
+
+    public void Validate()
+    {
+        if (HeartbeatInterval <= TimeSpan.Zero)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(HeartbeatInterval),
+                "Worker heartbeat interval must be greater than zero.");
+        }
+
+        if (HeartbeatGrace <= TimeSpan.Zero)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(HeartbeatGrace),
+                "Worker heartbeat grace must be greater than zero.");
+        }
+    }
+}

src/MxGateway.Worker/MxAccess/IMxAccessServer.cs

@@ -5,4 +5,17 @@ public interface IMxAccessServer
     int Register(string clientName);
 
     void Unregister(int serverHandle);
+
+    int AddItem(
+        int serverHandle,
+        string itemDefinition);
+
+    int AddItem2(
+        int serverHandle,
+        string itemDefinition,
+        string itemContext);
+
+    void RemoveItem(
+        int serverHandle,
+        int itemHandle);
 }

src/MxGateway.Worker/MxAccess/IWorkerRuntimeSession.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using MxGateway.Contracts.Proto;
+using MxGateway.Worker.Sta;
+
+namespace MxGateway.Worker.MxAccess;
+
+public interface IWorkerRuntimeSession : IDisposable
+{
+    Task<WorkerReady> StartAsync(
+        int workerProcessId,
+        CancellationToken cancellationToken = default);
+
+    Task<MxCommandReply> DispatchAsync(StaCommand command);
+
+    WorkerRuntimeHeartbeatSnapshot CaptureHeartbeat();
+
+    void RequestShutdown();
+}

src/MxGateway.Worker/MxAccess/MxAccessComServer.cs

@@ -35,6 +35,44 @@ public sealed class MxAccessComServer : IMxAccessServer
         Invoke(nameof(Unregister), serverHandle);
     }
 
+    public int AddItem(
+        int serverHandle,
+        string itemDefinition)
+    {
+        if (mxAccessComObject is ILMXProxyServer mxAccessServer)
+        {
+            return mxAccessServer.AddItem(serverHandle, itemDefinition);
+        }
+
+        return (int)Invoke(nameof(AddItem), serverHandle, itemDefinition);
+    }
+
+    public int AddItem2(
+        int serverHandle,
+        string itemDefinition,
+        string itemContext)
+    {
+        if (mxAccessComObject is ILMXProxyServer3 mxAccessServer)
+        {
+            return mxAccessServer.AddItem2(serverHandle, itemDefinition, itemContext);
+        }
+
+        return (int)Invoke(nameof(AddItem2), serverHandle, itemDefinition, itemContext);
+    }
+
+    public void RemoveItem(
+        int serverHandle,
+        int itemHandle)
+    {
+        if (mxAccessComObject is ILMXProxyServer mxAccessServer)
+        {
+            mxAccessServer.RemoveItem(serverHandle, itemHandle);
+            return;
+        }
+
+        Invoke(nameof(RemoveItem), serverHandle, itemHandle);
+    }
+
     private object Invoke(
         string methodName,
         params object[] arguments)

src/MxGateway.Worker/MxAccess/MxAccessCommandExecutor.cs

@@ -34,6 +34,9 @@ public sealed class MxAccessCommandExecutor : IStaCommandExecutor
         {
             MxCommandKind.Register => ExecuteRegister(command),
             MxCommandKind.Unregister => ExecuteUnregister(command),
+            MxCommandKind.AddItem => ExecuteAddItem(command),
+            MxCommandKind.AddItem2 => ExecuteAddItem2(command),
+            MxCommandKind.RemoveItem => ExecuteRemoveItem(command),
             _ => CreateInvalidRequestReply(command, $"Unsupported MXAccess command kind {command.Kind}."),
         };
     }
@@ -67,6 +70,66 @@ public sealed class MxAccessCommandExecutor : IStaCommandExecutor
         return CreateOkReply(command);
     }
 
+    private MxCommandReply ExecuteAddItem(StaCommand command)
+    {
+        if (command.Command.PayloadCase != MxCommand.PayloadOneofCase.AddItem)
+        {
+            return CreateInvalidRequestReply(command, "AddItem command payload is required.");
+        }
+
+        AddItemCommand addItemCommand = command.Command.AddItem;
+        int itemHandle = session.AddItem(
+            addItemCommand.ServerHandle,
+            addItemCommand.ItemDefinition);
+
+        MxCommandReply reply = CreateOkReply(command);
+        reply.ReturnValue = variantConverter.Convert(itemHandle);
+        reply.AddItem = new AddItemReply
+        {
+            ItemHandle = itemHandle,
+        };
+
+        return reply;
+    }
+
+    private MxCommandReply ExecuteAddItem2(StaCommand command)
+    {
+        if (command.Command.PayloadCase != MxCommand.PayloadOneofCase.AddItem2)
+        {
+            return CreateInvalidRequestReply(command, "AddItem2 command payload is required.");
+        }
+
+        AddItem2Command addItem2Command = command.Command.AddItem2;
+        int itemHandle = session.AddItem2(
+            addItem2Command.ServerHandle,
+            addItem2Command.ItemDefinition,
+            addItem2Command.ItemContext);
+
+        MxCommandReply reply = CreateOkReply(command);
+        reply.ReturnValue = variantConverter.Convert(itemHandle);
+        reply.AddItem2 = new AddItem2Reply
+        {
+            ItemHandle = itemHandle,
+        };
+
+        return reply;
+    }
+
+    private MxCommandReply ExecuteRemoveItem(StaCommand command)
+    {
+        if (command.Command.PayloadCase != MxCommand.PayloadOneofCase.RemoveItem)
+        {
+            return CreateInvalidRequestReply(command, "RemoveItem command payload is required.");
+        }
+
+        RemoveItemCommand removeItemCommand = command.Command.RemoveItem;
+        session.RemoveItem(
+            removeItemCommand.ServerHandle,
+            removeItemCommand.ItemHandle);
+
+        return CreateOkReply(command);
+    }
+
     private static MxCommandReply CreateOkReply(StaCommand command)
     {
         return new MxCommandReply

src/MxGateway.Worker/MxAccess/MxAccessHandleRegistry.cs

@@ -6,12 +6,19 @@ namespace MxGateway.Worker.MxAccess;
 public sealed class MxAccessHandleRegistry
 {
     private readonly Dictionary<int, RegisteredServerHandle> serverHandles = new();
+    private readonly Dictionary<long, RegisteredItemHandle> itemHandles = new();
 
     public IReadOnlyList<RegisteredServerHandle> ServerHandles => serverHandles
         .Values
         .OrderBy(handle => handle.ServerHandle)
         .ToArray();
 
+    public IReadOnlyList<RegisteredItemHandle> ItemHandles => itemHandles
+        .Values
+        .OrderBy(handle => handle.ServerHandle)
+        .ThenBy(handle => handle.ItemHandle)
+        .ToArray();
+
     public void RegisterServerHandle(
         int serverHandle,
         string clientName)
@@ -22,10 +29,54 @@ public sealed class MxAccessHandleRegistry
     public void UnregisterServerHandle(int serverHandle)
     {
         serverHandles.Remove(serverHandle);
+
+        foreach (long key in itemHandles
+            .Where(pair => pair.Value.ServerHandle == serverHandle)
+            .Select(pair => pair.Key)
+            .ToArray())
+        {
+            itemHandles.Remove(key);
+        }
     }
 
     public bool ContainsServerHandle(int serverHandle)
     {
         return serverHandles.ContainsKey(serverHandle);
     }
+
+    public void RegisterItemHandle(
+        int serverHandle,
+        int itemHandle,
+        string itemDefinition,
+        string itemContext,
+        bool hasItemContext)
+    {
+        itemHandles[CreateItemKey(serverHandle, itemHandle)] = new RegisteredItemHandle(
+            serverHandle,
+            itemHandle,
+            itemDefinition,
+            itemContext,
+            hasItemContext);
+    }
+
+    public void RemoveItemHandle(
+        int serverHandle,
+        int itemHandle)
+    {
+        itemHandles.Remove(CreateItemKey(serverHandle, itemHandle));
+    }
+
+    public bool ContainsItemHandle(
+        int serverHandle,
+        int itemHandle)
+    {
+        return itemHandles.ContainsKey(CreateItemKey(serverHandle, itemHandle));
+    }
+
+    private static long CreateItemKey(
+        int serverHandle,
+        int itemHandle)
+    {
+        return ((long)serverHandle << 32) | (uint)itemHandle;
+    }
 }

src/MxGateway.Worker/MxAccess/MxAccessSession.cs

@@ -106,6 +106,51 @@ public sealed class MxAccessSession : IDisposable
         handleRegistry.UnregisterServerHandle(serverHandle);
     }
 
+    public int AddItem(
+        int serverHandle,
+        string itemDefinition)
+    {
+        ThrowIfDisposed();
+
+        int itemHandle = mxAccessServer.AddItem(serverHandle, itemDefinition);
+        handleRegistry.RegisterItemHandle(
+            serverHandle,
+            itemHandle,
+            itemDefinition,
+            string.Empty,
+            hasItemContext: false);
+
+        return itemHandle;
+    }
+
+    public int AddItem2(
+        int serverHandle,
+        string itemDefinition,
+        string itemContext)
+    {
+        ThrowIfDisposed();
+
+        int itemHandle = mxAccessServer.AddItem2(serverHandle, itemDefinition, itemContext);
+        handleRegistry.RegisterItemHandle(
+            serverHandle,
+            itemHandle,
+            itemDefinition,
+            itemContext,
+            hasItemContext: true);
+
+        return itemHandle;
+    }
+
+    public void RemoveItem(
+        int serverHandle,
+        int itemHandle)
+    {
+        ThrowIfDisposed();
+
+        mxAccessServer.RemoveItem(serverHandle, itemHandle);
+        handleRegistry.RemoveItemHandle(serverHandle, itemHandle);
+    }
+
     public void Dispose()
     {
         if (disposed)

src/MxGateway.Worker/MxAccess/MxAccessStaSession.cs

@@ -7,7 +7,7 @@ using MxGateway.Worker.Sta;
 
 namespace MxGateway.Worker.MxAccess;
 
-public sealed class MxAccessStaSession : IDisposable
+public sealed class MxAccessStaSession : IWorkerRuntimeSession
 {
     private readonly IMxAccessComObjectFactory factory;
     private readonly IMxAccessEventSink eventSink;
@@ -68,6 +68,30 @@ public sealed class MxAccessStaSession : IDisposable
         return commandDispatcher.DispatchAsync(command);
     }
 
+    public WorkerRuntimeHeartbeatSnapshot CaptureHeartbeat()
+    {
+        uint pendingCommandCount = 0;
+        string currentCommandCorrelationId = string.Empty;
+
+        if (commandDispatcher is not null)
+        {
+            pendingCommandCount = (uint)commandDispatcher.PendingCommandCount;
+            currentCommandCorrelationId = commandDispatcher.CurrentCommandCorrelationId;
+        }
+
+        return new WorkerRuntimeHeartbeatSnapshot(
+            staRuntime.LastActivityUtc,
+            pendingCommandCount,
+            outboundEventQueueDepth: 0,
+            lastEventSequence: 0,
+            currentCommandCorrelationId);
+    }
+
+    public void RequestShutdown()
+    {
+        commandDispatcher?.RequestShutdown();
+    }
+
     public Task<IReadOnlyList<RegisteredServerHandle>> GetRegisteredServerHandlesAsync(
         CancellationToken cancellationToken = default)
     {
@@ -81,6 +105,19 @@ public sealed class MxAccessStaSession : IDisposable
             cancellationToken);
     }
 
+    public Task<IReadOnlyList<RegisteredItemHandle>> GetRegisteredItemHandlesAsync(
+        CancellationToken cancellationToken = default)
+    {
+        if (session is null)
+        {
+            throw new InvalidOperationException("MXAccess COM session has not been started.");
+        }
+
+        return staRuntime.InvokeAsync(
+            () => session.HandleRegistry.ItemHandles,
+            cancellationToken);
+    }
+
     public void Dispose()
     {
         if (disposed)
@@ -88,7 +125,7 @@ public sealed class MxAccessStaSession : IDisposable
             return;
         }
 
-        commandDispatcher?.RequestShutdown();
+        RequestShutdown();
 
         if (session is not null)
         {

src/MxGateway.Worker/MxAccess/RegisteredItemHandle.cs

@@ -0,0 +1,28 @@
+namespace MxGateway.Worker.MxAccess;
+
+public sealed class RegisteredItemHandle
+{
+    public RegisteredItemHandle(
+        int serverHandle,
+        int itemHandle,
+        string itemDefinition,
+        string itemContext,
+        bool hasItemContext)
+    {
+        ServerHandle = serverHandle;
+        ItemHandle = itemHandle;
+        ItemDefinition = itemDefinition;
+        ItemContext = itemContext;
+        HasItemContext = hasItemContext;
+    }
+
+    public int ServerHandle { get; }
+
+    public int ItemHandle { get; }
+
+    public string ItemDefinition { get; }
+
+    public string ItemContext { get; }
+
+    public bool HasItemContext { get; }
+}

src/MxGateway.Worker/MxAccess/WorkerRuntimeHeartbeatSnapshot.cs

@@ -0,0 +1,30 @@
+using System;
+
+namespace MxGateway.Worker.MxAccess;
+
+public sealed class WorkerRuntimeHeartbeatSnapshot
+{
+    public WorkerRuntimeHeartbeatSnapshot(
+        DateTimeOffset lastStaActivityUtc,
+        uint pendingCommandCount,
+        uint outboundEventQueueDepth,
+        ulong lastEventSequence,
+        string currentCommandCorrelationId)
+    {
+        LastStaActivityUtc = lastStaActivityUtc;
+        PendingCommandCount = pendingCommandCount;
+        OutboundEventQueueDepth = outboundEventQueueDepth;
+        LastEventSequence = lastEventSequence;
+        CurrentCommandCorrelationId = currentCommandCorrelationId ?? string.Empty;
+    }
+
+    public DateTimeOffset LastStaActivityUtc { get; }
+
+    public uint PendingCommandCount { get; }
+
+    public uint OutboundEventQueueDepth { get; }
+
+    public ulong LastEventSequence { get; }
+
+    public string CurrentCommandCorrelationId { get; }
+}

src/MxGateway.Worker/WorkerApplication.cs

@@ -84,7 +84,7 @@ public static class WorkerApplication
 
             pipeClient.RunAsync(options).GetAwaiter().GetResult();
 
-            logger.Information("WorkerPipeHandshakeSucceeded", new Dictionary<string, object?>
+            logger.Information("WorkerPipeSessionCompleted", new Dictionary<string, object?>
             {
                 ["session_id"] = options.SessionId,
                 ["pipe_name"] = options.PipeName,