Issue #9: implement worker frame protocol

Verified with dotnet build src\\MxGateway.sln and dotnet test src\\MxGateway.sln --no-build.

docs/Contracts.md

@@ -0,0 +1,46 @@
+# Protobuf Contracts
+
+The contracts project contains the public gRPC API and the gateway-to-worker
+IPC messages. The `.proto` files are the source of truth; generated C# files are
+recreated by the contracts project build.
+
+## Files
+
+`src/MxGateway.Contracts/Protos/mxaccess_gateway.proto` defines the public
+`MxAccessGateway` gRPC service, command payloads, command replies, event DTOs,
+`MxValue`, `MxArray`, and `MxStatusProxy`.
+
+`src/MxGateway.Contracts/Protos/mxaccess_worker.proto` defines the named-pipe
+worker IPC envelope and control messages. It imports
+`mxaccess_gateway.proto` so the worker and gateway use the same command, reply,
+event, value, and status shapes.
+
+Generated C# output is written to `src/MxGateway.Contracts/Generated/`. Do not
+hand-edit generated files.
+
+## Generation
+
+Run the contracts build to regenerate C# protobuf and gRPC code:
+
+```bash
+dotnet build src/MxGateway.Contracts/MxGateway.Contracts.csproj
+```
+
+Run the focused contract tests after changing either `.proto` file:
+
+```bash
+dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter ProtobufContractRoundTripTests
+```
+
+The full solution build also regenerates the C# contracts before compiling
+gateway and test projects:
+
+```bash
+dotnet build src/MxGateway.sln
+```
+
+## Related Documentation
+
+- [Gateway Process Detailed Design](./gateway-process-design.md)
+- [MXAccess Worker Instance Detailed Design](./mxaccess-worker-instance-design.md)
+- [Protobuf Style Guide](./style-guides/ProtobufStyleGuide.md)

docs/WorkerFrameProtocol.md

@@ -0,0 +1,54 @@
+# Worker Frame Protocol
+
+The gateway uses the worker frame protocol to move `WorkerEnvelope` protobuf
+messages over a bidirectional named pipe. The frame layer is deliberately small:
+it handles message boundaries, size limits, protobuf parsing, and envelope
+validation before higher-level worker client code routes commands, replies,
+events, and faults.
+
+## Frame Format
+
+Each frame starts with a four-byte little-endian unsigned payload length,
+followed by the serialized `WorkerEnvelope` payload:
+
+```text
+uint32 little-endian payload_length
+payload_length bytes protobuf WorkerEnvelope
+```
+
+The reader rejects zero-length payloads and payloads larger than the configured
+maximum before allocating the payload buffer. The default maximum is 16 MiB,
+matching the gateway process design.
+
+## Envelope Validation
+
+`WorkerFrameReader` and `WorkerFrameWriter` validate each envelope against the
+owning session before returning or writing it:
+
+- `protocol_version` must match the configured worker protocol version,
+- `session_id` must match the owning gateway session,
+- the envelope must contain one typed `body` value.
+
+Protocol violations throw `WorkerFrameProtocolException` with a
+`WorkerFrameProtocolErrorCode` so callers can distinguish malformed frames,
+oversized frames, protocol version mismatches, and session mismatches.
+
+## Verification
+
+Run the focused tests after changing the frame protocol:
+
+```bash
+dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter WorkerFrameProtocolTests
+```
+
+Run the gateway build because the frame protocol is part of
+`MxGateway.Server`:
+
+```bash
+dotnet build src/MxGateway.Server/MxGateway.Server.csproj
+```
+
+## Related Documentation
+
+- [Gateway Process Detailed Design](./gateway-process-design.md)
+- [Protobuf Contracts](./Contracts.md)

gateway.md

@@ -45,6 +45,8 @@ Detailed follow-up docs:
 - `docs/gateway-process-design.md` covers the .NET 10 gateway process,
   session manager, worker supervision, gRPC API, event streaming, fault model,
   security, observability, and test strategy.
+- `docs/WorkerFrameProtocol.md` covers the gateway-side named-pipe frame
+  reader/writer and `WorkerEnvelope` validation rules.
 - `docs/mxaccess-worker-instance-design.md` covers each .NET Framework 4.8 x86
   MXAccess worker instance, including STA ownership, message pumping, COM
   lifetime, command dispatch, event sinks, conversion, and shutdown.

src/MxGateway.Contracts/Generated/MxaccessGatewayGrpc.cs

@@ -0,0 +1,268 @@
+// <auto-generated>
+//     Generated by the protocol buffer compiler.  DO NOT EDIT!
+//     source: mxaccess_gateway.proto
+// </auto-generated>
+#pragma warning disable 0414, 1591, 8981, 0612
+#region Designer generated code
+
+using grpc = global::Grpc.Core;
+
+namespace MxGateway.Contracts.Proto {
+  /// <summary>
+  /// Public client API for MXAccess sessions hosted by the gateway.
+  /// </summary>
+  public static partial class MxAccessGateway
+  {
+    static readonly string __ServiceName = "mxaccess_gateway.v1.MxAccessGateway";
+
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static void __Helper_SerializeMessage(global::Google.Protobuf.IMessage message, grpc::SerializationContext context)
+    {
+      #if !GRPC_DISABLE_PROTOBUF_BUFFER_SERIALIZATION
+      if (message is global::Google.Protobuf.IBufferMessage)
+      {
+        context.SetPayloadLength(message.CalculateSize());
+        global::Google.Protobuf.MessageExtensions.WriteTo(message, context.GetBufferWriter());
+        context.Complete();
+        return;
+      }
+      #endif
+      context.Complete(global::Google.Protobuf.MessageExtensions.ToByteArray(message));
+    }
+
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static class __Helper_MessageCache<T>
+    {
+      public static readonly bool IsBufferMessage = global::System.Reflection.IntrospectionExtensions.GetTypeInfo(typeof(global::Google.Protobuf.IBufferMessage)).IsAssignableFrom(typeof(T));
+    }
+
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static T __Helper_DeserializeMessage<T>(grpc::DeserializationContext context, global::Google.Protobuf.MessageParser<T> parser) where T : global::Google.Protobuf.IMessage<T>
+    {
+      #if !GRPC_DISABLE_PROTOBUF_BUFFER_SERIALIZATION
+      if (__Helper_MessageCache<T>.IsBufferMessage)
+      {
+        return parser.ParseFrom(context.PayloadAsReadOnlySequence());
+      }
+      #endif
+      return parser.ParseFrom(context.PayloadAsNewBuffer());
+    }
+
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Marshaller<global::MxGateway.Contracts.Proto.OpenSessionRequest> __Marshaller_mxaccess_gateway_v1_OpenSessionRequest = grpc::Marshallers.Create(__Helper_SerializeMessage, context => __Helper_DeserializeMessage(context, global::MxGateway.Contracts.Proto.OpenSessionRequest.Parser));
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Marshaller<global::MxGateway.Contracts.Proto.OpenSessionReply> __Marshaller_mxaccess_gateway_v1_OpenSessionReply = grpc::Marshallers.Create(__Helper_SerializeMessage, context => __Helper_DeserializeMessage(context, global::MxGateway.Contracts.Proto.OpenSessionReply.Parser));
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Marshaller<global::MxGateway.Contracts.Proto.CloseSessionRequest> __Marshaller_mxaccess_gateway_v1_CloseSessionRequest = grpc::Marshallers.Create(__Helper_SerializeMessage, context => __Helper_DeserializeMessage(context, global::MxGateway.Contracts.Proto.CloseSessionRequest.Parser));
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Marshaller<global::MxGateway.Contracts.Proto.CloseSessionReply> __Marshaller_mxaccess_gateway_v1_CloseSessionReply = grpc::Marshallers.Create(__Helper_SerializeMessage, context => __Helper_DeserializeMessage(context, global::MxGateway.Contracts.Proto.CloseSessionReply.Parser));
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Marshaller<global::MxGateway.Contracts.Proto.MxCommandRequest> __Marshaller_mxaccess_gateway_v1_MxCommandRequest = grpc::Marshallers.Create(__Helper_SerializeMessage, context => __Helper_DeserializeMessage(context, global::MxGateway.Contracts.Proto.MxCommandRequest.Parser));
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Marshaller<global::MxGateway.Contracts.Proto.MxCommandReply> __Marshaller_mxaccess_gateway_v1_MxCommandReply = grpc::Marshallers.Create(__Helper_SerializeMessage, context => __Helper_DeserializeMessage(context, global::MxGateway.Contracts.Proto.MxCommandReply.Parser));
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Marshaller<global::MxGateway.Contracts.Proto.StreamEventsRequest> __Marshaller_mxaccess_gateway_v1_StreamEventsRequest = grpc::Marshallers.Create(__Helper_SerializeMessage, context => __Helper_DeserializeMessage(context, global::MxGateway.Contracts.Proto.StreamEventsRequest.Parser));
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Marshaller<global::MxGateway.Contracts.Proto.MxEvent> __Marshaller_mxaccess_gateway_v1_MxEvent = grpc::Marshallers.Create(__Helper_SerializeMessage, context => __Helper_DeserializeMessage(context, global::MxGateway.Contracts.Proto.MxEvent.Parser));
+
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Method<global::MxGateway.Contracts.Proto.OpenSessionRequest, global::MxGateway.Contracts.Proto.OpenSessionReply> __Method_OpenSession = new grpc::Method<global::MxGateway.Contracts.Proto.OpenSessionRequest, global::MxGateway.Contracts.Proto.OpenSessionReply>(
+        grpc::MethodType.Unary,
+        __ServiceName,
+        "OpenSession",
+        __Marshaller_mxaccess_gateway_v1_OpenSessionRequest,
+        __Marshaller_mxaccess_gateway_v1_OpenSessionReply);
+
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Method<global::MxGateway.Contracts.Proto.CloseSessionRequest, global::MxGateway.Contracts.Proto.CloseSessionReply> __Method_CloseSession = new grpc::Method<global::MxGateway.Contracts.Proto.CloseSessionRequest, global::MxGateway.Contracts.Proto.CloseSessionReply>(
+        grpc::MethodType.Unary,
+        __ServiceName,
+        "CloseSession",
+        __Marshaller_mxaccess_gateway_v1_CloseSessionRequest,
+        __Marshaller_mxaccess_gateway_v1_CloseSessionReply);
+
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Method<global::MxGateway.Contracts.Proto.MxCommandRequest, global::MxGateway.Contracts.Proto.MxCommandReply> __Method_Invoke = new grpc::Method<global::MxGateway.Contracts.Proto.MxCommandRequest, global::MxGateway.Contracts.Proto.MxCommandReply>(
+        grpc::MethodType.Unary,
+        __ServiceName,
+        "Invoke",
+        __Marshaller_mxaccess_gateway_v1_MxCommandRequest,
+        __Marshaller_mxaccess_gateway_v1_MxCommandReply);
+
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    static readonly grpc::Method<global::MxGateway.Contracts.Proto.StreamEventsRequest, global::MxGateway.Contracts.Proto.MxEvent> __Method_StreamEvents = new grpc::Method<global::MxGateway.Contracts.Proto.StreamEventsRequest, global::MxGateway.Contracts.Proto.MxEvent>(
+        grpc::MethodType.ServerStreaming,
+        __ServiceName,
+        "StreamEvents",
+        __Marshaller_mxaccess_gateway_v1_StreamEventsRequest,
+        __Marshaller_mxaccess_gateway_v1_MxEvent);
+
+    /// <summary>Service descriptor</summary>
+    public static global::Google.Protobuf.Reflection.ServiceDescriptor Descriptor
+    {
+      get { return global::MxGateway.Contracts.Proto.MxaccessGatewayReflection.Descriptor.Services[0]; }
+    }
+
+    /// <summary>Base class for server-side implementations of MxAccessGateway</summary>
+    [grpc::BindServiceMethod(typeof(MxAccessGateway), "BindService")]
+    public abstract partial class MxAccessGatewayBase
+    {
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::System.Threading.Tasks.Task<global::MxGateway.Contracts.Proto.OpenSessionReply> OpenSession(global::MxGateway.Contracts.Proto.OpenSessionRequest request, grpc::ServerCallContext context)
+      {
+        throw new grpc::RpcException(new grpc::Status(grpc::StatusCode.Unimplemented, ""));
+      }
+
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::System.Threading.Tasks.Task<global::MxGateway.Contracts.Proto.CloseSessionReply> CloseSession(global::MxGateway.Contracts.Proto.CloseSessionRequest request, grpc::ServerCallContext context)
+      {
+        throw new grpc::RpcException(new grpc::Status(grpc::StatusCode.Unimplemented, ""));
+      }
+
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::System.Threading.Tasks.Task<global::MxGateway.Contracts.Proto.MxCommandReply> Invoke(global::MxGateway.Contracts.Proto.MxCommandRequest request, grpc::ServerCallContext context)
+      {
+        throw new grpc::RpcException(new grpc::Status(grpc::StatusCode.Unimplemented, ""));
+      }
+
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::System.Threading.Tasks.Task StreamEvents(global::MxGateway.Contracts.Proto.StreamEventsRequest request, grpc::IServerStreamWriter<global::MxGateway.Contracts.Proto.MxEvent> responseStream, grpc::ServerCallContext context)
+      {
+        throw new grpc::RpcException(new grpc::Status(grpc::StatusCode.Unimplemented, ""));
+      }
+
+    }
+
+    /// <summary>Client for MxAccessGateway</summary>
+    public partial class MxAccessGatewayClient : grpc::ClientBase<MxAccessGatewayClient>
+    {
+      /// <summary>Creates a new client for MxAccessGateway</summary>
+      /// <param name="channel">The channel to use to make remote calls.</param>
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public MxAccessGatewayClient(grpc::ChannelBase channel) : base(channel)
+      {
+      }
+      /// <summary>Creates a new client for MxAccessGateway that uses a custom <c>CallInvoker</c>.</summary>
+      /// <param name="callInvoker">The callInvoker to use to make remote calls.</param>
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public MxAccessGatewayClient(grpc::CallInvoker callInvoker) : base(callInvoker)
+      {
+      }
+      /// <summary>Protected parameterless constructor to allow creation of test doubles.</summary>
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      protected MxAccessGatewayClient() : base()
+      {
+      }
+      /// <summary>Protected constructor to allow creation of configured clients.</summary>
+      /// <param name="configuration">The client configuration.</param>
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      protected MxAccessGatewayClient(ClientBaseConfiguration configuration) : base(configuration)
+      {
+      }
+
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::MxGateway.Contracts.Proto.OpenSessionReply OpenSession(global::MxGateway.Contracts.Proto.OpenSessionRequest request, grpc::Metadata headers = null, global::System.DateTime? deadline = null, global::System.Threading.CancellationToken cancellationToken = default(global::System.Threading.CancellationToken))
+      {
+        return OpenSession(request, new grpc::CallOptions(headers, deadline, cancellationToken));
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::MxGateway.Contracts.Proto.OpenSessionReply OpenSession(global::MxGateway.Contracts.Proto.OpenSessionRequest request, grpc::CallOptions options)
+      {
+        return CallInvoker.BlockingUnaryCall(__Method_OpenSession, null, options, request);
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual grpc::AsyncUnaryCall<global::MxGateway.Contracts.Proto.OpenSessionReply> OpenSessionAsync(global::MxGateway.Contracts.Proto.OpenSessionRequest request, grpc::Metadata headers = null, global::System.DateTime? deadline = null, global::System.Threading.CancellationToken cancellationToken = default(global::System.Threading.CancellationToken))
+      {
+        return OpenSessionAsync(request, new grpc::CallOptions(headers, deadline, cancellationToken));
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual grpc::AsyncUnaryCall<global::MxGateway.Contracts.Proto.OpenSessionReply> OpenSessionAsync(global::MxGateway.Contracts.Proto.OpenSessionRequest request, grpc::CallOptions options)
+      {
+        return CallInvoker.AsyncUnaryCall(__Method_OpenSession, null, options, request);
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::MxGateway.Contracts.Proto.CloseSessionReply CloseSession(global::MxGateway.Contracts.Proto.CloseSessionRequest request, grpc::Metadata headers = null, global::System.DateTime? deadline = null, global::System.Threading.CancellationToken cancellationToken = default(global::System.Threading.CancellationToken))
+      {
+        return CloseSession(request, new grpc::CallOptions(headers, deadline, cancellationToken));
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::MxGateway.Contracts.Proto.CloseSessionReply CloseSession(global::MxGateway.Contracts.Proto.CloseSessionRequest request, grpc::CallOptions options)
+      {
+        return CallInvoker.BlockingUnaryCall(__Method_CloseSession, null, options, request);
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual grpc::AsyncUnaryCall<global::MxGateway.Contracts.Proto.CloseSessionReply> CloseSessionAsync(global::MxGateway.Contracts.Proto.CloseSessionRequest request, grpc::Metadata headers = null, global::System.DateTime? deadline = null, global::System.Threading.CancellationToken cancellationToken = default(global::System.Threading.CancellationToken))
+      {
+        return CloseSessionAsync(request, new grpc::CallOptions(headers, deadline, cancellationToken));
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual grpc::AsyncUnaryCall<global::MxGateway.Contracts.Proto.CloseSessionReply> CloseSessionAsync(global::MxGateway.Contracts.Proto.CloseSessionRequest request, grpc::CallOptions options)
+      {
+        return CallInvoker.AsyncUnaryCall(__Method_CloseSession, null, options, request);
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::MxGateway.Contracts.Proto.MxCommandReply Invoke(global::MxGateway.Contracts.Proto.MxCommandRequest request, grpc::Metadata headers = null, global::System.DateTime? deadline = null, global::System.Threading.CancellationToken cancellationToken = default(global::System.Threading.CancellationToken))
+      {
+        return Invoke(request, new grpc::CallOptions(headers, deadline, cancellationToken));
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual global::MxGateway.Contracts.Proto.MxCommandReply Invoke(global::MxGateway.Contracts.Proto.MxCommandRequest request, grpc::CallOptions options)
+      {
+        return CallInvoker.BlockingUnaryCall(__Method_Invoke, null, options, request);
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual grpc::AsyncUnaryCall<global::MxGateway.Contracts.Proto.MxCommandReply> InvokeAsync(global::MxGateway.Contracts.Proto.MxCommandRequest request, grpc::Metadata headers = null, global::System.DateTime? deadline = null, global::System.Threading.CancellationToken cancellationToken = default(global::System.Threading.CancellationToken))
+      {
+        return InvokeAsync(request, new grpc::CallOptions(headers, deadline, cancellationToken));
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual grpc::AsyncUnaryCall<global::MxGateway.Contracts.Proto.MxCommandReply> InvokeAsync(global::MxGateway.Contracts.Proto.MxCommandRequest request, grpc::CallOptions options)
+      {
+        return CallInvoker.AsyncUnaryCall(__Method_Invoke, null, options, request);
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual grpc::AsyncServerStreamingCall<global::MxGateway.Contracts.Proto.MxEvent> StreamEvents(global::MxGateway.Contracts.Proto.StreamEventsRequest request, grpc::Metadata headers = null, global::System.DateTime? deadline = null, global::System.Threading.CancellationToken cancellationToken = default(global::System.Threading.CancellationToken))
+      {
+        return StreamEvents(request, new grpc::CallOptions(headers, deadline, cancellationToken));
+      }
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      public virtual grpc::AsyncServerStreamingCall<global::MxGateway.Contracts.Proto.MxEvent> StreamEvents(global::MxGateway.Contracts.Proto.StreamEventsRequest request, grpc::CallOptions options)
+      {
+        return CallInvoker.AsyncServerStreamingCall(__Method_StreamEvents, null, options, request);
+      }
+      /// <summary>Creates a new instance of client from given <c>ClientBaseConfiguration</c>.</summary>
+      [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+      protected override MxAccessGatewayClient NewInstance(ClientBaseConfiguration configuration)
+      {
+        return new MxAccessGatewayClient(configuration);
+      }
+    }
+
+    /// <summary>Creates service definition that can be registered with a server</summary>
+    /// <param name="serviceImpl">An object implementing the server-side handling logic.</param>
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    public static grpc::ServerServiceDefinition BindService(MxAccessGatewayBase serviceImpl)
+    {
+      return grpc::ServerServiceDefinition.CreateBuilder()
+          .AddMethod(__Method_OpenSession, serviceImpl.OpenSession)
+          .AddMethod(__Method_CloseSession, serviceImpl.CloseSession)
+          .AddMethod(__Method_Invoke, serviceImpl.Invoke)
+          .AddMethod(__Method_StreamEvents, serviceImpl.StreamEvents).Build();
+    }
+
+    /// <summary>Register service method with a service binder with or without implementation. Useful when customizing the service binding logic.
+    /// Note: this method is part of an experimental API that can change or be removed without any prior notice.</summary>
+    /// <param name="serviceBinder">Service methods will be bound by calling <c>AddMethod</c> on this object.</param>
+    /// <param name="serviceImpl">An object implementing the server-side handling logic.</param>
+    [global::System.CodeDom.Compiler.GeneratedCode("grpc_csharp_plugin", null)]
+    public static void BindService(grpc::ServiceBinderBase serviceBinder, MxAccessGatewayBase serviceImpl)
+    {
+      serviceBinder.AddMethod(__Method_OpenSession, serviceImpl == null ? null : new grpc::UnaryServerMethod<global::MxGateway.Contracts.Proto.OpenSessionRequest, global::MxGateway.Contracts.Proto.OpenSessionReply>(serviceImpl.OpenSession));
+      serviceBinder.AddMethod(__Method_CloseSession, serviceImpl == null ? null : new grpc::UnaryServerMethod<global::MxGateway.Contracts.Proto.CloseSessionRequest, global::MxGateway.Contracts.Proto.CloseSessionReply>(serviceImpl.CloseSession));
+      serviceBinder.AddMethod(__Method_Invoke, serviceImpl == null ? null : new grpc::UnaryServerMethod<global::MxGateway.Contracts.Proto.MxCommandRequest, global::MxGateway.Contracts.Proto.MxCommandReply>(serviceImpl.Invoke));
+      serviceBinder.AddMethod(__Method_StreamEvents, serviceImpl == null ? null : new grpc::ServerStreamingServerMethod<global::MxGateway.Contracts.Proto.StreamEventsRequest, global::MxGateway.Contracts.Proto.MxEvent>(serviceImpl.StreamEvents));
+    }
+
+  }
+}
+#endregion

src/MxGateway.Contracts/MxGateway.Contracts.csproj

@@ -4,4 +4,19 @@
     <TargetFramework>net10.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+    <Compile Remove="Generated\**\*.cs" />
+    <Protobuf Include="Protos\mxaccess_gateway.proto" ProtoRoot="Protos" OutputDir="Generated" GrpcOutputDir="Generated" GrpcServices="Both" />
+    <Protobuf Include="Protos\mxaccess_worker.proto" ProtoRoot="Protos" OutputDir="Generated" GrpcServices="None" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Google.Protobuf" Version="3.34.1" />
+    <PackageReference Include="Grpc.Core.Api" Version="2.76.0" />
+    <PackageReference Include="Grpc.Tools" Version="2.80.0">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
 </Project>

src/MxGateway.Contracts/Protos/mxaccess_gateway.proto

@@ -0,0 +1,521 @@
+syntax = "proto3";
+
+package mxaccess_gateway.v1;
+
+option csharp_namespace = "MxGateway.Contracts.Proto";
+
+import "google/protobuf/duration.proto";
+import "google/protobuf/timestamp.proto";
+
+// Public client API for MXAccess sessions hosted by the gateway.
+service MxAccessGateway {
+  rpc OpenSession(OpenSessionRequest) returns (OpenSessionReply);
+  rpc CloseSession(CloseSessionRequest) returns (CloseSessionReply);
+  rpc Invoke(MxCommandRequest) returns (MxCommandReply);
+  rpc StreamEvents(StreamEventsRequest) returns (stream MxEvent);
+}
+
+message OpenSessionRequest {
+  string requested_backend = 1;
+  string client_session_name = 2;
+  string client_correlation_id = 3;
+  google.protobuf.Duration command_timeout = 4;
+}
+
+message OpenSessionReply {
+  string session_id = 1;
+  string backend_name = 2;
+  int32 worker_process_id = 3;
+  uint32 worker_protocol_version = 4;
+  repeated string capabilities = 5;
+  google.protobuf.Duration default_command_timeout = 6;
+  ProtocolStatus protocol_status = 7;
+}
+
+message CloseSessionRequest {
+  string session_id = 1;
+  string client_correlation_id = 2;
+}
+
+message CloseSessionReply {
+  string session_id = 1;
+  SessionState final_state = 2;
+  ProtocolStatus protocol_status = 3;
+}
+
+message StreamEventsRequest {
+  string session_id = 1;
+  uint64 after_worker_sequence = 2;
+}
+
+message MxCommandRequest {
+  string session_id = 1;
+  string client_correlation_id = 2;
+  MxCommand command = 3;
+}
+
+message MxCommand {
+  MxCommandKind kind = 1;
+
+  oneof payload {
+    RegisterCommand register = 10;
+    UnregisterCommand unregister = 11;
+    AddItemCommand add_item = 12;
+    AddItem2Command add_item2 = 13;
+    RemoveItemCommand remove_item = 14;
+    AdviseCommand advise = 15;
+    UnAdviseCommand un_advise = 16;
+    AdviseSupervisoryCommand advise_supervisory = 17;
+    AddBufferedItemCommand add_buffered_item = 18;
+    SetBufferedUpdateIntervalCommand set_buffered_update_interval = 19;
+    SuspendCommand suspend = 20;
+    ActivateCommand activate = 21;
+    WriteCommand write = 22;
+    Write2Command write2 = 23;
+    WriteSecuredCommand write_secured = 24;
+    WriteSecured2Command write_secured2 = 25;
+    AuthenticateUserCommand authenticate_user = 26;
+    ArchestrAUserToIdCommand archestra_user_to_id = 27;
+    PingCommand ping = 100;
+    GetSessionStateCommand get_session_state = 101;
+    GetWorkerInfoCommand get_worker_info = 102;
+    DrainEventsCommand drain_events = 103;
+    ShutdownWorkerCommand shutdown_worker = 104;
+  }
+}
+
+enum MxCommandKind {
+  MX_COMMAND_KIND_UNSPECIFIED = 0;
+  MX_COMMAND_KIND_REGISTER = 1;
+  MX_COMMAND_KIND_UNREGISTER = 2;
+  MX_COMMAND_KIND_ADD_ITEM = 3;
+  MX_COMMAND_KIND_ADD_ITEM2 = 4;
+  MX_COMMAND_KIND_REMOVE_ITEM = 5;
+  MX_COMMAND_KIND_ADVISE = 6;
+  MX_COMMAND_KIND_UN_ADVISE = 7;
+  MX_COMMAND_KIND_ADVISE_SUPERVISORY = 8;
+  MX_COMMAND_KIND_ADD_BUFFERED_ITEM = 9;
+  MX_COMMAND_KIND_SET_BUFFERED_UPDATE_INTERVAL = 10;
+  MX_COMMAND_KIND_SUSPEND = 11;
+  MX_COMMAND_KIND_ACTIVATE = 12;
+  MX_COMMAND_KIND_WRITE = 13;
+  MX_COMMAND_KIND_WRITE2 = 14;
+  MX_COMMAND_KIND_WRITE_SECURED = 15;
+  MX_COMMAND_KIND_WRITE_SECURED2 = 16;
+  MX_COMMAND_KIND_AUTHENTICATE_USER = 17;
+  MX_COMMAND_KIND_ARCHESTRA_USER_TO_ID = 18;
+  MX_COMMAND_KIND_PING = 100;
+  MX_COMMAND_KIND_GET_SESSION_STATE = 101;
+  MX_COMMAND_KIND_GET_WORKER_INFO = 102;
+  MX_COMMAND_KIND_DRAIN_EVENTS = 103;
+  MX_COMMAND_KIND_SHUTDOWN_WORKER = 104;
+}
+
+message RegisterCommand {
+  string client_name = 1;
+}
+
+message UnregisterCommand {
+  int32 server_handle = 1;
+}
+
+message AddItemCommand {
+  int32 server_handle = 1;
+  string item_definition = 2;
+}
+
+message AddItem2Command {
+  int32 server_handle = 1;
+  string item_definition = 2;
+  string item_context = 3;
+}
+
+message RemoveItemCommand {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+}
+
+message AdviseCommand {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+}
+
+message UnAdviseCommand {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+}
+
+message AdviseSupervisoryCommand {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+}
+
+message AddBufferedItemCommand {
+  int32 server_handle = 1;
+  string item_definition = 2;
+  string item_context = 3;
+}
+
+message SetBufferedUpdateIntervalCommand {
+  int32 server_handle = 1;
+  int32 update_interval_milliseconds = 2;
+}
+
+message SuspendCommand {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+}
+
+message ActivateCommand {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+}
+
+message WriteCommand {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+  MxValue value = 3;
+  int32 user_id = 4;
+}
+
+message Write2Command {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+  MxValue value = 3;
+  MxValue timestamp_value = 4;
+  int32 user_id = 5;
+}
+
+message WriteSecuredCommand {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+  int32 current_user_id = 3;
+  int32 verifier_user_id = 4;
+  // Credential-sensitive write value. Implementations must not log this field
+  // unless an explicit redacted value-logging path is enabled.
+  MxValue value = 5;
+}
+
+message WriteSecured2Command {
+  int32 server_handle = 1;
+  int32 item_handle = 2;
+  int32 current_user_id = 3;
+  int32 verifier_user_id = 4;
+  // Credential-sensitive write value. Implementations must not log this field
+  // unless an explicit redacted value-logging path is enabled.
+  MxValue value = 5;
+  MxValue timestamp_value = 6;
+}
+
+message AuthenticateUserCommand {
+  int32 server_handle = 1;
+  string verify_user = 2;
+  // Raw MXAccess credential. Implementations must keep this field out of logs,
+  // metrics labels, command lines, and diagnostics.
+  string verify_user_password = 3;
+}
+
+message ArchestrAUserToIdCommand {
+  int32 server_handle = 1;
+  string user_id_guid = 2;
+}
+
+message PingCommand {
+  string message = 1;
+}
+
+message GetSessionStateCommand {
+}
+
+message GetWorkerInfoCommand {
+}
+
+message DrainEventsCommand {
+  uint32 max_events = 1;
+}
+
+message ShutdownWorkerCommand {
+  google.protobuf.Duration grace_period = 1;
+}
+
+message MxCommandReply {
+  string session_id = 1;
+  string correlation_id = 2;
+  MxCommandKind kind = 3;
+  ProtocolStatus protocol_status = 4;
+  // HRESULT captured from MXAccess or a COM exception. This remains separate
+  // from gateway protocol status so MXAccess parity details are not hidden by
+  // transport failures.
+  optional int32 hresult = 5;
+  MxValue return_value = 6;
+  repeated MxStatusProxy statuses = 7;
+  string diagnostic_message = 8;
+
+  oneof payload {
+    RegisterReply register = 20;
+    AddItemReply add_item = 21;
+    AddItem2Reply add_item2 = 22;
+    AddBufferedItemReply add_buffered_item = 23;
+    SuspendReply suspend = 24;
+    ActivateReply activate = 25;
+    AuthenticateUserReply authenticate_user = 26;
+    ArchestrAUserToIdReply archestra_user_to_id = 27;
+    SessionStateReply session_state = 100;
+    WorkerInfoReply worker_info = 101;
+    DrainEventsReply drain_events = 102;
+  }
+}
+
+message RegisterReply {
+  int32 server_handle = 1;
+}
+
+message AddItemReply {
+  int32 item_handle = 1;
+}
+
+message AddItem2Reply {
+  int32 item_handle = 1;
+}
+
+message AddBufferedItemReply {
+  int32 item_handle = 1;
+}
+
+message SuspendReply {
+  MxStatusProxy status = 1;
+}
+
+message ActivateReply {
+  MxStatusProxy status = 1;
+}
+
+message AuthenticateUserReply {
+  int32 user_id = 1;
+}
+
+message ArchestrAUserToIdReply {
+  int32 user_id = 1;
+}
+
+message SessionStateReply {
+  SessionState state = 1;
+}
+
+message WorkerInfoReply {
+  int32 worker_process_id = 1;
+  string worker_version = 2;
+  string mxaccess_progid = 3;
+  string mxaccess_clsid = 4;
+}
+
+message DrainEventsReply {
+  repeated MxEvent events = 1;
+}
+
+message MxEvent {
+  MxEventFamily family = 1;
+  string session_id = 2;
+  int32 server_handle = 3;
+  int32 item_handle = 4;
+  MxValue value = 5;
+  int32 quality = 6;
+  google.protobuf.Timestamp source_timestamp = 7;
+  repeated MxStatusProxy statuses = 8;
+  uint64 worker_sequence = 9;
+  google.protobuf.Timestamp worker_timestamp = 10;
+  google.protobuf.Timestamp gateway_receive_timestamp = 11;
+  optional int32 hresult = 12;
+  string raw_status = 13;
+
+  oneof body {
+    OnDataChangeEvent on_data_change = 20;
+    OnWriteCompleteEvent on_write_complete = 21;
+    OperationCompleteEvent operation_complete = 22;
+    OnBufferedDataChangeEvent on_buffered_data_change = 23;
+  }
+}
+
+enum MxEventFamily {
+  MX_EVENT_FAMILY_UNSPECIFIED = 0;
+  MX_EVENT_FAMILY_ON_DATA_CHANGE = 1;
+  MX_EVENT_FAMILY_ON_WRITE_COMPLETE = 2;
+  MX_EVENT_FAMILY_OPERATION_COMPLETE = 3;
+  MX_EVENT_FAMILY_ON_BUFFERED_DATA_CHANGE = 4;
+}
+
+message OnDataChangeEvent {
+}
+
+message OnWriteCompleteEvent {
+}
+
+message OperationCompleteEvent {
+}
+
+message OnBufferedDataChangeEvent {
+  MxDataType data_type = 1;
+  MxArray quality_values = 2;
+  MxArray timestamp_values = 3;
+  int32 raw_data_type = 4;
+}
+
+message MxStatusProxy {
+  int32 success = 1;
+  MxStatusCategory category = 2;
+  MxStatusSource detected_by = 3;
+  int32 detail = 4;
+  int32 raw_category = 5;
+  int32 raw_detected_by = 6;
+  string diagnostic_text = 7;
+}
+
+enum MxStatusCategory {
+  MX_STATUS_CATEGORY_UNSPECIFIED = 0;
+  MX_STATUS_CATEGORY_UNKNOWN = 1;
+  MX_STATUS_CATEGORY_OK = 2;
+  MX_STATUS_CATEGORY_PENDING = 3;
+  MX_STATUS_CATEGORY_WARNING = 4;
+  MX_STATUS_CATEGORY_COMMUNICATION_ERROR = 5;
+  MX_STATUS_CATEGORY_CONFIGURATION_ERROR = 6;
+  MX_STATUS_CATEGORY_OPERATIONAL_ERROR = 7;
+  MX_STATUS_CATEGORY_SECURITY_ERROR = 8;
+  MX_STATUS_CATEGORY_SOFTWARE_ERROR = 9;
+  MX_STATUS_CATEGORY_OTHER_ERROR = 10;
+}
+
+enum MxStatusSource {
+  MX_STATUS_SOURCE_UNSPECIFIED = 0;
+  MX_STATUS_SOURCE_UNKNOWN = 1;
+  MX_STATUS_SOURCE_REQUESTING_LMX = 2;
+  MX_STATUS_SOURCE_RESPONDING_LMX = 3;
+  MX_STATUS_SOURCE_REQUESTING_NMX = 4;
+  MX_STATUS_SOURCE_RESPONDING_NMX = 5;
+  MX_STATUS_SOURCE_REQUESTING_AUTOMATION_OBJECT = 6;
+  MX_STATUS_SOURCE_RESPONDING_AUTOMATION_OBJECT = 7;
+}
+
+message MxValue {
+  MxDataType data_type = 1;
+  string variant_type = 2;
+  bool is_null = 3;
+  string raw_diagnostic = 4;
+  int32 raw_data_type = 5;
+
+  oneof kind {
+    bool bool_value = 10;
+    int32 int32_value = 11;
+    int64 int64_value = 12;
+    float float_value = 13;
+    double double_value = 14;
+    string string_value = 15;
+    google.protobuf.Timestamp timestamp_value = 16;
+    MxArray array_value = 17;
+    bytes raw_value = 18;
+  }
+}
+
+message MxArray {
+  MxDataType element_data_type = 1;
+  string variant_type = 2;
+  repeated uint32 dimensions = 3;
+  string raw_diagnostic = 4;
+  int32 raw_element_data_type = 5;
+
+  oneof values {
+    BoolArray bool_values = 10;
+    Int32Array int32_values = 11;
+    Int64Array int64_values = 12;
+    FloatArray float_values = 13;
+    DoubleArray double_values = 14;
+    StringArray string_values = 15;
+    TimestampArray timestamp_values = 16;
+    RawArray raw_values = 17;
+  }
+}
+
+message BoolArray {
+  repeated bool values = 1;
+}
+
+message Int32Array {
+  repeated int32 values = 1;
+}
+
+message Int64Array {
+  repeated int64 values = 1;
+}
+
+message FloatArray {
+  repeated float values = 1;
+}
+
+message DoubleArray {
+  repeated double values = 1;
+}
+
+message StringArray {
+  repeated string values = 1;
+}
+
+message TimestampArray {
+  repeated google.protobuf.Timestamp values = 1;
+}
+
+message RawArray {
+  repeated bytes values = 1;
+}
+
+enum MxDataType {
+  MX_DATA_TYPE_UNSPECIFIED = 0;
+  MX_DATA_TYPE_UNKNOWN = 1;
+  MX_DATA_TYPE_NO_DATA = 2;
+  MX_DATA_TYPE_BOOLEAN = 3;
+  MX_DATA_TYPE_INTEGER = 4;
+  MX_DATA_TYPE_FLOAT = 5;
+  MX_DATA_TYPE_DOUBLE = 6;
+  MX_DATA_TYPE_STRING = 7;
+  MX_DATA_TYPE_TIME = 8;
+  MX_DATA_TYPE_ELAPSED_TIME = 9;
+  MX_DATA_TYPE_REFERENCE_TYPE = 10;
+  MX_DATA_TYPE_STATUS_TYPE = 11;
+  MX_DATA_TYPE_ENUM = 12;
+  MX_DATA_TYPE_SECURITY_CLASSIFICATION_ENUM = 13;
+  MX_DATA_TYPE_DATA_QUALITY_TYPE = 14;
+  MX_DATA_TYPE_QUALIFIED_ENUM = 15;
+  MX_DATA_TYPE_QUALIFIED_STRUCT = 16;
+  MX_DATA_TYPE_INTERNATIONALIZED_STRING = 17;
+  MX_DATA_TYPE_BIG_STRING = 18;
+  MX_DATA_TYPE_END = 19;
+}
+
+message ProtocolStatus {
+  ProtocolStatusCode code = 1;
+  string message = 2;
+}
+
+enum ProtocolStatusCode {
+  PROTOCOL_STATUS_CODE_UNSPECIFIED = 0;
+  PROTOCOL_STATUS_CODE_OK = 1;
+  PROTOCOL_STATUS_CODE_INVALID_REQUEST = 2;
+  PROTOCOL_STATUS_CODE_SESSION_NOT_FOUND = 3;
+  PROTOCOL_STATUS_CODE_SESSION_NOT_READY = 4;
+  PROTOCOL_STATUS_CODE_WORKER_UNAVAILABLE = 5;
+  PROTOCOL_STATUS_CODE_TIMEOUT = 6;
+  PROTOCOL_STATUS_CODE_CANCELED = 7;
+  PROTOCOL_STATUS_CODE_PROTOCOL_VIOLATION = 8;
+  PROTOCOL_STATUS_CODE_MXACCESS_FAILURE = 9;
+}
+
+enum SessionState {
+  SESSION_STATE_UNSPECIFIED = 0;
+  SESSION_STATE_CREATING = 1;
+  SESSION_STATE_STARTING_WORKER = 2;
+  SESSION_STATE_WAITING_FOR_PIPE = 3;
+  SESSION_STATE_HANDSHAKING = 4;
+  SESSION_STATE_INITIALIZING_WORKER = 5;
+  SESSION_STATE_READY = 6;
+  SESSION_STATE_CLOSING = 7;
+  SESSION_STATE_CLOSED = 8;
+  SESSION_STATE_FAULTED = 9;
+}

src/MxGateway.Contracts/Protos/mxaccess_worker.proto

@@ -0,0 +1,125 @@
+syntax = "proto3";
+
+package mxaccess_worker.v1;
+
+option csharp_namespace = "MxGateway.Contracts.Proto";
+
+import "google/protobuf/duration.proto";
+import "google/protobuf/timestamp.proto";
+import "mxaccess_gateway.proto";
+
+// Gateway-to-worker IPC envelope. Named-pipe framing prepends a little-endian
+// uint32 payload length to this protobuf payload.
+message WorkerEnvelope {
+  uint32 protocol_version = 1;
+  string session_id = 2;
+  uint64 sequence = 3;
+  string correlation_id = 4;
+
+  oneof body {
+    GatewayHello gateway_hello = 10;
+    WorkerHello worker_hello = 11;
+    WorkerReady worker_ready = 12;
+    WorkerCommand worker_command = 13;
+    WorkerCommandReply worker_command_reply = 14;
+    WorkerCancel worker_cancel = 15;
+    WorkerShutdown worker_shutdown = 16;
+    WorkerShutdownAck worker_shutdown_ack = 17;
+    WorkerEvent worker_event = 18;
+    WorkerHeartbeat worker_heartbeat = 19;
+    WorkerFault worker_fault = 20;
+  }
+}
+
+message GatewayHello {
+  uint32 supported_protocol_version = 1;
+  string nonce = 2;
+  string gateway_version = 3;
+}
+
+message WorkerHello {
+  uint32 protocol_version = 1;
+  string nonce = 2;
+  int32 worker_process_id = 3;
+  string worker_version = 4;
+}
+
+message WorkerReady {
+  int32 worker_process_id = 1;
+  string mxaccess_progid = 2;
+  string mxaccess_clsid = 3;
+  google.protobuf.Timestamp ready_timestamp = 4;
+}
+
+message WorkerCommand {
+  mxaccess_gateway.v1.MxCommand command = 1;
+  google.protobuf.Timestamp enqueue_timestamp = 2;
+}
+
+message WorkerCommandReply {
+  mxaccess_gateway.v1.MxCommandReply reply = 1;
+  google.protobuf.Timestamp completed_timestamp = 2;
+}
+
+message WorkerCancel {
+  string reason = 1;
+}
+
+message WorkerShutdown {
+  google.protobuf.Duration grace_period = 1;
+  string reason = 2;
+}
+
+message WorkerShutdownAck {
+  mxaccess_gateway.v1.ProtocolStatus status = 1;
+}
+
+message WorkerEvent {
+  mxaccess_gateway.v1.MxEvent event = 1;
+}
+
+message WorkerHeartbeat {
+  int32 worker_process_id = 1;
+  WorkerState state = 2;
+  google.protobuf.Timestamp last_sta_activity_timestamp = 3;
+  uint32 pending_command_count = 4;
+  uint32 outbound_event_queue_depth = 5;
+  uint64 last_event_sequence = 6;
+  string current_command_correlation_id = 7;
+}
+
+message WorkerFault {
+  WorkerFaultCategory category = 1;
+  string command_method = 2;
+  optional int32 hresult = 3;
+  string exception_type = 4;
+  string diagnostic_message = 5;
+  mxaccess_gateway.v1.ProtocolStatus protocol_status = 6;
+}
+
+enum WorkerState {
+  WORKER_STATE_UNSPECIFIED = 0;
+  WORKER_STATE_STARTING = 1;
+  WORKER_STATE_HANDSHAKING = 2;
+  WORKER_STATE_INITIALIZING_STA = 3;
+  WORKER_STATE_READY = 4;
+  WORKER_STATE_EXECUTING_COMMAND = 5;
+  WORKER_STATE_SHUTTING_DOWN = 6;
+  WORKER_STATE_STOPPED = 7;
+  WORKER_STATE_FAULTED = 8;
+}
+
+enum WorkerFaultCategory {
+  WORKER_FAULT_CATEGORY_UNSPECIFIED = 0;
+  WORKER_FAULT_CATEGORY_INVALID_ARGUMENTS = 1;
+  WORKER_FAULT_CATEGORY_GATEWAY_AUTHENTICATION_FAILED = 2;
+  WORKER_FAULT_CATEGORY_PROTOCOL_MISMATCH = 3;
+  WORKER_FAULT_CATEGORY_PROTOCOL_VIOLATION = 4;
+  WORKER_FAULT_CATEGORY_PIPE_DISCONNECTED = 5;
+  WORKER_FAULT_CATEGORY_MXACCESS_CREATION_FAILED = 6;
+  WORKER_FAULT_CATEGORY_MXACCESS_COMMAND_FAILED = 7;
+  WORKER_FAULT_CATEGORY_MXACCESS_EVENT_CONVERSION_FAILED = 8;
+  WORKER_FAULT_CATEGORY_STA_HUNG = 9;
+  WORKER_FAULT_CATEGORY_QUEUE_OVERFLOW = 10;
+  WORKER_FAULT_CATEGORY_SHUTDOWN_TIMEOUT = 11;
+}

src/MxGateway.Server/Workers/WorkerEnvelopeValidator.cs

@@ -0,0 +1,32 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Server.Workers;
+
+internal static class WorkerEnvelopeValidator
+{
+    public static void Validate(
+        WorkerEnvelope envelope,
+        WorkerFrameProtocolOptions options)
+    {
+        if (envelope.ProtocolVersion != options.ProtocolVersion)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.ProtocolVersionMismatch,
+                $"Worker envelope protocol version {envelope.ProtocolVersion} does not match expected version {options.ProtocolVersion}.");
+        }
+
+        if (!string.Equals(envelope.SessionId, options.SessionId, StringComparison.Ordinal))
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.SessionMismatch,
+                "Worker envelope session id does not match the owning gateway session.");
+        }
+
+        if (envelope.BodyCase == WorkerEnvelope.BodyOneofCase.None)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.InvalidEnvelope,
+                "Worker envelope must include a typed body.");
+        }
+    }
+}

src/MxGateway.Server/Workers/WorkerFrameProtocolErrorCode.cs

@@ -0,0 +1,13 @@
+namespace MxGateway.Server.Workers;
+
+public enum WorkerFrameProtocolErrorCode
+{
+    Unknown = 0,
+    InvalidConfiguration = 1,
+    EndOfStream = 2,
+    MalformedLength = 3,
+    MessageTooLarge = 4,
+    InvalidEnvelope = 5,
+    ProtocolVersionMismatch = 6,
+    SessionMismatch = 7,
+}

src/MxGateway.Server/Workers/WorkerFrameProtocolException.cs

@@ -0,0 +1,23 @@
+namespace MxGateway.Server.Workers;
+
+public sealed class WorkerFrameProtocolException : Exception
+{
+    public WorkerFrameProtocolException(
+        WorkerFrameProtocolErrorCode errorCode,
+        string message)
+        : base(message)
+    {
+        ErrorCode = errorCode;
+    }
+
+    public WorkerFrameProtocolException(
+        WorkerFrameProtocolErrorCode errorCode,
+        string message,
+        Exception innerException)
+        : base(message, innerException)
+    {
+        ErrorCode = errorCode;
+    }
+
+    public WorkerFrameProtocolErrorCode ErrorCode { get; }
+}

src/MxGateway.Server/Workers/WorkerFrameProtocolOptions.cs

@@ -0,0 +1,53 @@
+using MxGateway.Contracts;
+
+namespace MxGateway.Server.Workers;
+
+public sealed class WorkerFrameProtocolOptions
+{
+    public const int DefaultMaxMessageBytes = 16 * 1024 * 1024;
+
+    public WorkerFrameProtocolOptions(string sessionId)
+        : this(
+            sessionId,
+            GatewayContractInfo.WorkerProtocolVersion,
+            DefaultMaxMessageBytes)
+    {
+    }
+
+    public WorkerFrameProtocolOptions(
+        string sessionId,
+        uint protocolVersion,
+        int maxMessageBytes)
+    {
+        if (string.IsNullOrWhiteSpace(sessionId))
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.InvalidConfiguration,
+                "Worker frame protocol requires a session id.");
+        }
+
+        if (protocolVersion == 0)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.InvalidConfiguration,
+                "Worker frame protocol requires a non-zero protocol version.");
+        }
+
+        if (maxMessageBytes <= 0)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.InvalidConfiguration,
+                "Worker frame protocol max message size must be greater than zero.");
+        }
+
+        SessionId = sessionId;
+        ProtocolVersion = protocolVersion;
+        MaxMessageBytes = maxMessageBytes;
+    }
+
+    public string SessionId { get; }
+
+    public uint ProtocolVersion { get; }
+
+    public int MaxMessageBytes { get; }
+}

src/MxGateway.Server/Workers/WorkerFrameReader.cs

@@ -0,0 +1,77 @@
+using System.Buffers.Binary;
+using Google.Protobuf;
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Server.Workers;
+
+public sealed class WorkerFrameReader
+{
+    private readonly WorkerFrameProtocolOptions _options;
+    private readonly Stream _stream;
+
+    public WorkerFrameReader(
+        Stream stream,
+        WorkerFrameProtocolOptions options)
+    {
+        _stream = stream ?? throw new ArgumentNullException(nameof(stream));
+        _options = options ?? throw new ArgumentNullException(nameof(options));
+    }
+
+    public async ValueTask<WorkerEnvelope> ReadAsync(CancellationToken cancellationToken = default)
+    {
+        byte[] lengthPrefix = new byte[sizeof(uint)];
+        await ReadExactlyOrThrowAsync(lengthPrefix, cancellationToken).ConfigureAwait(false);
+
+        uint payloadLength = BinaryPrimitives.ReadUInt32LittleEndian(lengthPrefix);
+        if (payloadLength == 0)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.MalformedLength,
+                "Worker frame payload length must be greater than zero.");
+        }
+
+        if (payloadLength > _options.MaxMessageBytes)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.MessageTooLarge,
+                $"Worker frame payload length {payloadLength} exceeds the configured maximum of {_options.MaxMessageBytes} bytes.");
+        }
+
+        byte[] payload = new byte[payloadLength];
+        await ReadExactlyOrThrowAsync(payload, cancellationToken).ConfigureAwait(false);
+
+        WorkerEnvelope envelope;
+        try
+        {
+            envelope = WorkerEnvelope.Parser.ParseFrom(payload);
+        }
+        catch (InvalidProtocolBufferException exception)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.InvalidEnvelope,
+                "Worker frame payload is not a valid WorkerEnvelope protobuf message.",
+                exception);
+        }
+
+        WorkerEnvelopeValidator.Validate(envelope, _options);
+
+        return envelope;
+    }
+
+    private async ValueTask ReadExactlyOrThrowAsync(
+        Memory<byte> buffer,
+        CancellationToken cancellationToken)
+    {
+        try
+        {
+            await _stream.ReadExactlyAsync(buffer, cancellationToken).ConfigureAwait(false);
+        }
+        catch (EndOfStreamException exception)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.EndOfStream,
+                "Worker frame ended before the expected number of bytes were read.",
+                exception);
+        }
+    }
+}

src/MxGateway.Server/Workers/WorkerFrameWriter.cs

@@ -0,0 +1,48 @@
+using System.Buffers.Binary;
+using Google.Protobuf;
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Server.Workers;
+
+public sealed class WorkerFrameWriter
+{
+    private readonly WorkerFrameProtocolOptions _options;
+    private readonly Stream _stream;
+
+    public WorkerFrameWriter(
+        Stream stream,
+        WorkerFrameProtocolOptions options)
+    {
+        _stream = stream ?? throw new ArgumentNullException(nameof(stream));
+        _options = options ?? throw new ArgumentNullException(nameof(options));
+    }
+
+    public async ValueTask WriteAsync(
+        WorkerEnvelope envelope,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(envelope);
+        WorkerEnvelopeValidator.Validate(envelope, _options);
+
+        int payloadLength = envelope.CalculateSize();
+        if (payloadLength == 0)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.InvalidEnvelope,
+                "Worker envelope cannot serialize to an empty payload.");
+        }
+
+        if (payloadLength > _options.MaxMessageBytes)
+        {
+            throw new WorkerFrameProtocolException(
+                WorkerFrameProtocolErrorCode.MessageTooLarge,
+                $"Worker envelope payload length {payloadLength} exceeds the configured maximum of {_options.MaxMessageBytes} bytes.");
+        }
+
+        byte[] lengthPrefix = new byte[sizeof(uint)];
+        BinaryPrimitives.WriteUInt32LittleEndian(lengthPrefix, (uint)payloadLength);
+
+        await _stream.WriteAsync(lengthPrefix, cancellationToken).ConfigureAwait(false);
+        await _stream.WriteAsync(envelope.ToByteArray(), cancellationToken).ConfigureAwait(false);
+    }
+}

src/MxGateway.Tests/Contracts/ProtobufContractRoundTripTests.cs

@@ -0,0 +1,195 @@
+using Google.Protobuf;
+using Google.Protobuf.WellKnownTypes;
+using MxGateway.Contracts;
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Tests.Contracts;
+
+public sealed class ProtobufContractRoundTripTests
+{
+    [Fact]
+    public void GatewayDescriptor_ContainsInitialPublicServiceMethods()
+    {
+        var service = Assert.Single(
+            MxaccessGatewayReflection.Descriptor.Services,
+            descriptor => descriptor.Name == "MxAccessGateway");
+
+        Assert.Contains(service.Methods, method => method.Name == "OpenSession");
+        Assert.Contains(service.Methods, method => method.Name == "CloseSession");
+        Assert.Contains(service.Methods, method => method.Name == "Invoke");
+        Assert.Contains(service.Methods, method => method.Name == "StreamEvents");
+    }
+
+    [Fact]
+    public void WorkerEnvelopeDescriptor_ContainsRequiredCorrelationFields()
+    {
+        var fields = WorkerEnvelope.Descriptor.Fields.InDeclarationOrder();
+
+        Assert.Contains(fields, field => field.Name == "protocol_version");
+        Assert.Contains(fields, field => field.Name == "session_id");
+        Assert.Contains(fields, field => field.Name == "sequence");
+        Assert.Contains(fields, field => field.Name == "correlation_id");
+    }
+
+    [Fact]
+    public void CommandRequest_RoundTripsMethodSpecificPayload()
+    {
+        var original = new MxCommandRequest
+        {
+            SessionId = "session-1",
+            ClientCorrelationId = "client-correlation-1",
+            Command = new MxCommand
+            {
+                Kind = MxCommandKind.Register,
+                Register = new RegisterCommand
+                {
+                    ClientName = "mxaccessgw-test-client",
+                },
+            },
+        };
+
+        var parsed = MxCommandRequest.Parser.ParseFrom(original.ToByteArray());
+
+        Assert.Equal(original, parsed);
+        Assert.Equal(MxCommand.PayloadOneofCase.Register, parsed.Command.PayloadCase);
+    }
+
+    [Fact]
+    public void CommandReply_RoundTripsHResultReturnValueOutParamsAndStatuses()
+    {
+        var original = new MxCommandReply
+        {
+            SessionId = "session-1",
+            CorrelationId = "gateway-correlation-1",
+            Kind = MxCommandKind.AddItem,
+            ProtocolStatus = new ProtocolStatus
+            {
+                Code = ProtocolStatusCode.Ok,
+            },
+            Hresult = 0,
+            ReturnValue = new MxValue
+            {
+                DataType = MxDataType.Integer,
+                Int32Value = 1234,
+                VariantType = "VT_I4",
+            },
+            AddItem = new AddItemReply
+            {
+                ItemHandle = 1234,
+            },
+        };
+        original.Statuses.Add(new MxStatusProxy
+        {
+            Success = 1,
+            Category = MxStatusCategory.Ok,
+            DetectedBy = MxStatusSource.RespondingLmx,
+            Detail = 0,
+        });
+
+        var parsed = MxCommandReply.Parser.ParseFrom(original.ToByteArray());
+
+        Assert.Equal(original, parsed);
+        Assert.True(parsed.HasHresult);
+        Assert.Equal(MxCommandReply.PayloadOneofCase.AddItem, parsed.PayloadCase);
+        Assert.Single(parsed.Statuses);
+    }
+
+    [Fact]
+    public void Event_RoundTripsValueStatusSequenceAndBufferedBody()
+    {
+        var timestamp = Timestamp.FromDateTime(new DateTime(2026, 4, 26, 20, 0, 0, DateTimeKind.Utc));
+        var original = new MxEvent
+        {
+            Family = MxEventFamily.OnBufferedDataChange,
+            SessionId = "session-1",
+            ServerHandle = 10,
+            ItemHandle = 20,
+            Value = new MxValue
+            {
+                DataType = MxDataType.Float,
+                ArrayValue = new MxArray
+                {
+                    ElementDataType = MxDataType.Float,
+                    FloatValues = new FloatArray
+                    {
+                        Values = { 1.5f, 2.5f },
+                    },
+                    Dimensions = { 2 },
+                    VariantType = "VT_ARRAY|VT_R4",
+                },
+            },
+            Quality = 192,
+            SourceTimestamp = timestamp,
+            WorkerSequence = 42,
+            WorkerTimestamp = timestamp,
+            GatewayReceiveTimestamp = timestamp,
+            OnBufferedDataChange = new OnBufferedDataChangeEvent
+            {
+                DataType = MxDataType.Float,
+                QualityValues = new MxArray
+                {
+                    ElementDataType = MxDataType.Integer,
+                    Int32Values = new Int32Array
+                    {
+                        Values = { 192, 192 },
+                    },
+                    Dimensions = { 2 },
+                },
+                TimestampValues = new MxArray
+                {
+                    ElementDataType = MxDataType.Time,
+                    TimestampValues = new TimestampArray
+                    {
+                        Values = { timestamp, timestamp },
+                    },
+                    Dimensions = { 2 },
+                },
+            },
+        };
+        original.Statuses.Add(new MxStatusProxy
+        {
+            Success = 1,
+            Category = MxStatusCategory.Ok,
+            DetectedBy = MxStatusSource.RespondingNmx,
+            Detail = 0,
+        });
+
+        var parsed = MxEvent.Parser.ParseFrom(original.ToByteArray());
+
+        Assert.Equal(original, parsed);
+        Assert.Equal(MxEvent.BodyOneofCase.OnBufferedDataChange, parsed.BodyCase);
+        Assert.Single(parsed.Statuses);
+    }
+
+    [Fact]
+    public void WorkerEnvelope_RoundTripsProtocolFieldsAndCommandBody()
+    {
+        var original = new WorkerEnvelope
+        {
+            ProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
+            SessionId = "session-1",
+            Sequence = 7,
+            CorrelationId = "gateway-correlation-1",
+            WorkerCommand = new WorkerCommand
+            {
+                EnqueueTimestamp = Timestamp.FromDateTime(
+                    new DateTime(2026, 4, 26, 20, 5, 0, DateTimeKind.Utc)),
+                Command = new MxCommand
+                {
+                    Kind = MxCommandKind.Advise,
+                    Advise = new AdviseCommand
+                    {
+                        ServerHandle = 10,
+                        ItemHandle = 20,
+                    },
+                },
+            },
+        };
+
+        var parsed = WorkerEnvelope.Parser.ParseFrom(original.ToByteArray());
+
+        Assert.Equal(original, parsed);
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerCommand, parsed.BodyCase);
+        Assert.Equal(MxCommand.PayloadOneofCase.Advise, parsed.WorkerCommand.Command.PayloadCase);
+    }
+}

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

@@ -0,0 +1,209 @@
+using System.Buffers.Binary;
+using Google.Protobuf;
+using MxGateway.Contracts;
+using MxGateway.Contracts.Proto;
+using MxGateway.Server.Workers;
+
+namespace MxGateway.Tests.Gateway.Workers;
+
+public sealed class WorkerFrameProtocolTests
+{
+    private const string SessionId = "session-1";
+
+    [Fact]
+    public async Task WriteAndReadAsync_WithValidEnvelope_RoundTripsFrame()
+    {
+        WorkerFrameProtocolOptions options = new(SessionId);
+        await using MemoryStream stream = new();
+        WorkerEnvelope original = CreateEnvelope();
+
+        WorkerFrameWriter writer = new(stream, options);
+        await writer.WriteAsync(original);
+        stream.Position = 0;
+
+        WorkerFrameReader reader = new(stream, options);
+        WorkerEnvelope parsed = await reader.ReadAsync();
+
+        Assert.Equal(original, parsed);
+    }
+
+    [Fact]
+    public async Task ReadAsync_WithPartialReads_ReassemblesFrame()
+    {
+        WorkerFrameProtocolOptions options = new(SessionId);
+        WorkerEnvelope original = CreateEnvelope();
+        byte[] frame = CreateFrame(original);
+        await using ChunkedReadStream stream = new(frame, chunkSize: 2);
+
+        WorkerFrameReader reader = new(stream, options);
+        WorkerEnvelope parsed = await reader.ReadAsync();
+
+        Assert.Equal(original, parsed);
+        Assert.True(stream.ReadCallCount > 2);
+    }
+
+    [Fact]
+    public async Task ReadAsync_WithZeroLengthFrame_ThrowsMalformedLength()
+    {
+        WorkerFrameProtocolOptions options = new(SessionId);
+        await using MemoryStream stream = new(new byte[sizeof(uint)]);
+
+        WorkerFrameReader reader = new(stream, options);
+        WorkerFrameProtocolException exception =
+            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
+                async () => await reader.ReadAsync());
+
+        Assert.Equal(WorkerFrameProtocolErrorCode.MalformedLength, exception.ErrorCode);
+    }
+
+    [Fact]
+    public async Task ReadAsync_WithOversizedLength_ThrowsBeforePayloadAllocation()
+    {
+        WorkerFrameProtocolOptions options = new(SessionId, GatewayContractInfo.WorkerProtocolVersion, maxMessageBytes: 16);
+        byte[] lengthPrefix = new byte[sizeof(uint)];
+        BinaryPrimitives.WriteUInt32LittleEndian(lengthPrefix, 17);
+        await using MemoryStream stream = new(lengthPrefix);
+
+        WorkerFrameReader reader = new(stream, options);
+        WorkerFrameProtocolException exception =
+            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
+                async () => await reader.ReadAsync());
+
+        Assert.Equal(WorkerFrameProtocolErrorCode.MessageTooLarge, exception.ErrorCode);
+    }
+
+    [Fact]
+    public async Task ReadAsync_WithWrongProtocolVersion_ThrowsProtocolVersionMismatch()
+    {
+        WorkerFrameProtocolOptions options = new(SessionId);
+        WorkerEnvelope envelope = CreateEnvelope();
+        envelope.ProtocolVersion++;
+        await using MemoryStream stream = new(CreateFrame(envelope));
+
+        WorkerFrameReader reader = new(stream, options);
+        WorkerFrameProtocolException exception =
+            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
+                async () => await reader.ReadAsync());
+
+        Assert.Equal(WorkerFrameProtocolErrorCode.ProtocolVersionMismatch, exception.ErrorCode);
+    }
+
+    [Fact]
+    public async Task ReadAsync_WithWrongSessionId_ThrowsSessionMismatch()
+    {
+        WorkerFrameProtocolOptions options = new(SessionId);
+        WorkerEnvelope envelope = CreateEnvelope();
+        envelope.SessionId = "different-session";
+        await using MemoryStream stream = new(CreateFrame(envelope));
+
+        WorkerFrameReader reader = new(stream, options);
+        WorkerFrameProtocolException exception =
+            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
+                async () => await reader.ReadAsync());
+
+        Assert.Equal(WorkerFrameProtocolErrorCode.SessionMismatch, exception.ErrorCode);
+    }
+
+    [Fact]
+    public async Task ReadAsync_WithMalformedPayload_ThrowsInvalidEnvelope()
+    {
+        WorkerFrameProtocolOptions options = new(SessionId);
+        byte[] frame = CreateFrame([0x80]);
+        await using MemoryStream stream = new(frame);
+
+        WorkerFrameReader reader = new(stream, options);
+        WorkerFrameProtocolException exception =
+            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
+                async () => await reader.ReadAsync());
+
+        Assert.Equal(WorkerFrameProtocolErrorCode.InvalidEnvelope, exception.ErrorCode);
+    }
+
+    [Fact]
+    public async Task ReadAsync_WithMissingEnvelopeBody_ThrowsInvalidEnvelope()
+    {
+        WorkerFrameProtocolOptions options = new(SessionId);
+        WorkerEnvelope envelope = CreateEnvelope();
+        envelope.ClearBody();
+        await using MemoryStream stream = new(CreateFrame(envelope));
+
+        WorkerFrameReader reader = new(stream, options);
+        WorkerFrameProtocolException exception =
+            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
+                async () => await reader.ReadAsync());
+
+        Assert.Equal(WorkerFrameProtocolErrorCode.InvalidEnvelope, exception.ErrorCode);
+    }
+
+    [Fact]
+    public async Task WriteAsync_WithOversizedEnvelope_ThrowsMessageTooLarge()
+    {
+        WorkerFrameProtocolOptions options = new(SessionId, GatewayContractInfo.WorkerProtocolVersion, maxMessageBytes: 8);
+        await using MemoryStream stream = new();
+
+        WorkerFrameWriter writer = new(stream, options);
+        WorkerFrameProtocolException exception =
+            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
+                async () => await writer.WriteAsync(CreateEnvelope()));
+
+        Assert.Equal(WorkerFrameProtocolErrorCode.MessageTooLarge, exception.ErrorCode);
+        Assert.Equal(0, stream.Length);
+    }
+
+    private static WorkerEnvelope CreateEnvelope()
+    {
+        return new WorkerEnvelope
+        {
+            ProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
+            SessionId = SessionId,
+            Sequence = 1,
+            CorrelationId = "correlation-1",
+            WorkerHello = new WorkerHello
+            {
+                ProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
+                Nonce = "nonce",
+                WorkerProcessId = 1234,
+                WorkerVersion = "test-worker",
+            },
+        };
+    }
+
+    private static byte[] CreateFrame(IMessage message)
+    {
+        return CreateFrame(message.ToByteArray());
+    }
+
+    private static byte[] CreateFrame(byte[] payload)
+    {
+        byte[] frame = new byte[sizeof(uint) + payload.Length];
+        BinaryPrimitives.WriteUInt32LittleEndian(frame.AsSpan(0, sizeof(uint)), (uint)payload.Length);
+        payload.CopyTo(frame.AsSpan(sizeof(uint)));
+
+        return frame;
+    }
+
+    private sealed class ChunkedReadStream : MemoryStream
+    {
+        private readonly int _chunkSize;
+
+        public ChunkedReadStream(
+            byte[] buffer,
+            int chunkSize)
+            : base(buffer)
+        {
+            _chunkSize = chunkSize;
+        }
+
+        public int ReadCallCount { get; private set; }
+
+        public override ValueTask<int> ReadAsync(
+            Memory<byte> buffer,
+            CancellationToken cancellationToken = default)
+        {
+            ReadCallCount++;
+            int requestedCount = Math.Min(buffer.Length, _chunkSize);
+
+            return base.ReadAsync(buffer[..requestedCount], cancellationToken);
+        }
+    }
+}