Track CaptureForReview test helper

Bring the per-step screenshot helper (TestCaptureExtensions.CaptureForReview)
into tree without yet adding the call sites — the existing instrumented
test files stay clean for now and can be re-instrumented selectively
when needed.

Assisted-by: Claude:claude-opus-4-7:Claude Code

ILSpy.Tests/TestCaptureExtensions.cs

@@ -0,0 +1,69 @@
+// Copyright (c) 2026 AlphaSierraPapa for the SharpDevelop Team
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System;
+using System.IO;
+using System.Linq;
+using System.Runtime.CompilerServices;
+
+using Avalonia.Controls;
+using Avalonia.Headless;
+using Avalonia.Threading;
+
+namespace ICSharpCode.ILSpy.Tests;
+
+/// <summary>
+/// Deterministic-path screenshot helpers for the test-review workflow. Unlike
+/// <see cref="WindowExtensions.CaptureAndShow"/> these don't open the OS image viewer —
+/// they write to <c>%TEMP%/ilspy-test-captures/</c> with a filename predictable from
+/// the (testName, step, label) triple so the audit workflow can read them back for
+/// in-chat review. The <c>ILSPY_TEST_CAPTURES</c> environment variable overrides the
+/// directory when a specific machine wants captures elsewhere. Only renders when
+/// <c>ILSPY_TESTS_VISIBLE=1</c> (otherwise the headless platform returns a null frame
+/// and the call is a no-op).
+/// </summary>
+public static class TestCaptureExtensions
+{
+	static readonly string OutputDirectory = Environment.GetEnvironmentVariable("ILSPY_TEST_CAPTURES")
+		?? Path.Combine(Path.GetTempPath(), "ilspy-test-captures");
+
+	public static void CaptureForReview(
+		this Window window,
+		int step,
+		string label,
+		[CallerMemberName] string? testName = null)
+	{
+		ArgumentNullException.ThrowIfNull(window);
+		Dispatcher.UIThread.RunJobs();
+		var frame = window.CaptureRenderedFrame();
+		if (frame is null)
+			return;
+
+		Directory.CreateDirectory(OutputDirectory);
+		var fileName = $"{Sanitize(testName)}-{step:D2}-{Sanitize(label)}.png";
+		var path = Path.Combine(OutputDirectory, fileName);
+		frame.Save(path);
+	}
+
+	static string Sanitize(string? label)
+	{
+		if (string.IsNullOrWhiteSpace(label))
+			return "frame";
+		return new string(label.Select(c => char.IsLetterOrDigit(c) ? c : '_').ToArray());
+	}
+}