Add XML documentation across gateway, worker, and .NET client

clients/dotnet/MxGateway.Client.Tests/MxCommandReplyExtensionsTests.cs

@@ -6,6 +6,7 @@ namespace MxGateway.Client.Tests;
 
 public sealed class MxCommandReplyExtensionsTests
 {
+    /// <summary>Verifies that successful replies pass both protocol and MxAccess success checks.</summary>
     [Fact]
     public void EnsureSuccess_WithRegisterFixture_ReturnsReply()
     {
@@ -15,6 +16,7 @@ public sealed class MxCommandReplyExtensionsTests
         Assert.Same(reply, reply.EnsureMxAccessSuccess());
     }
 
+    /// <summary>Verifies that MxAccess failures throw with preserved HResult and status details.</summary>
     [Fact]
     public void EnsureMxAccessSuccess_WithFailureFixture_PreservesHResultAndStatuses()
     {
@@ -30,6 +32,7 @@ public sealed class MxCommandReplyExtensionsTests
         Assert.Contains("0x80040200", exception.Message);
     }
 
+    /// <summary>Verifies that session-not-found protocol failures throw the correct gateway exception.</summary>
     [Fact]
     public void EnsureProtocolSuccess_WithSessionFailure_ThrowsSessionException()
     {