feat: HtmlReporter publishes SessionFileArtifact after writing report

Implements IDataProducer on HtmlReporter with DataTypesProduced=[SessionFileArtifact]
and calls PublishArtifactAsync after writing the HTML file so the platform can
surface the report as a session artifact. Adds unit tests to verify the interface
and DataTypesProduced contract.

TUnit.Engine.Tests/HtmlReporterTests.cs

@@ -0,0 +1,35 @@
+#pragma warning disable TPEXP
+
+using Microsoft.Testing.Platform.Extensions;
+using Microsoft.Testing.Platform.Extensions.Messages;
+using Shouldly;
+using TUnit.Engine.Reporters.Html;
+
+namespace TUnit.Engine.Tests;
+
+public class HtmlReporterTests
+{
+    private sealed class MockExtension : IExtension
+    {
+        public string Uid => "MockExtension";
+        public string DisplayName => "Mock";
+        public string Version => "1.0.0";
+        public string Description => "Mock Extension";
+        public Task<bool> IsEnabledAsync() => Task.FromResult(true);
+    }
+
+    [Test]
+    public void HtmlReporter_Implements_IDataProducer()
+    {
+        var reporter = new HtmlReporter(new MockExtension());
+        reporter.ShouldBeAssignableTo<Microsoft.Testing.Platform.Extensions.Messages.IDataProducer>();
+    }
+
+    [Test]
+    public void HtmlReporter_DataTypesProduced_Contains_SessionFileArtifact()
+    {
+        var reporter = new HtmlReporter(new MockExtension());
+        var producer = (Microsoft.Testing.Platform.Extensions.Messages.IDataProducer)reporter;
+        producer.DataTypesProduced.ShouldContain(typeof(SessionFileArtifact));
+    }
+}

TUnit.Engine.Tests/TUnit.Engine.Tests.csproj

@@ -7,7 +7,8 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="Microsoft.Testing.Extensions.CrashDump" />
+        <PackageReference Include="Microsoft.Testing.Platform" />
+    <PackageReference Include="Microsoft.Testing.Extensions.CrashDump" />
         <PackageReference Include="Microsoft.Testing.Extensions.HangDump" />
         <PackageReference Include="Microsoft.Testing.Extensions.TrxReport" />
         <PackageReference Include="CliWrap" />

TUnit.Engine/Reporters/Html/HtmlReporter.cs

@@ -18,12 +18,10 @@
 
 namespace TUnit.Engine.Reporters.Html;
 
-internal sealed class HtmlReporter(IExtension extension) : IDataConsumer, ITestHostApplicationLifetime, IFilterReceiver, IDisposable
+public sealed class HtmlReporter(IExtension extension) : IDataConsumer, IDataProducer, ITestHostApplicationLifetime, IFilterReceiver, IDisposable
 {
     private string? _outputPath;
-#pragma warning disable CS0414 // Field assigned but value never used — consumed in Task 2
     private (IMessageBus MessageBus, SessionUid SessionUid)? _sessionContext;
-#pragma warning restore CS0414
     private readonly ConcurrentDictionary<string, ConcurrentQueue<TestNodeUpdateMessage>> _updates = [];
 
 #if NET
@@ -61,6 +59,8 @@ public Task ConsumeAsync(IDataProducer dataProducer, IData value, CancellationTo
 
     public Type[] DataTypesConsumed { get; } = [typeof(TestNodeUpdateMessage)];
 
+    public Type[] DataTypesProduced { get; } = [typeof(SessionFileArtifact)];
+
     public Task BeforeRunAsync(CancellationToken cancellationToken)
     {
         if (string.IsNullOrEmpty(_outputPath))
@@ -112,6 +112,8 @@ public async Task AfterRunAsync(int exitCode, CancellationToken cancellation)
 
             await WriteFileAsync(_outputPath!, html, cancellation);
 
+            await PublishArtifactAsync(_outputPath!, cancellation);
+
             // GitHub Actions integration (artifact upload + step summary)
             await TryGitHubIntegrationAsync(_outputPath!, cancellation);
         }
@@ -121,6 +123,26 @@ public async Task AfterRunAsync(int exitCode, CancellationToken cancellation)
         }
     }
 
+    private async Task PublishArtifactAsync(string outputPath, CancellationToken cancellationToken)
+    {
+        if (_sessionContext is not { } ctx)
+        {
+            return;
+        }
+
+        var file = new FileInfo(outputPath);
+        if (!file.Exists)
+        {
+            return;
+        }
+
+        await ctx.MessageBus.PublishAsync(this, new SessionFileArtifact(
+            ctx.SessionUid,
+            file,
+            "HTML Test Report",
+            "TUnit HTML test results report"));
+    }
+
     public void Dispose()
     {
 #if NET