Skip Finder and Explorer metadata files instead of counting them as failed [patch]

Directory.Build.props

@@ -1,2 +1,16 @@
 <Project>
+  <!--
+    SixLabors.ImageSharp 3.1.12 is the last 3.1.x release and carries these advisories; no 3.1.x
+    release patches them. The fix is 4.x, which moved to a split licence, so the package is pinned to
+    3.1.x deliberately and these are accepted until ImageSharp is upgraded or replaced. Each advisory
+    is named individually so a new one still fails the restore. Revisit this list on every ImageSharp
+    bump, and keep it the only place these are declared: a second copy fails restore with NU1508.
+  -->
+  <ItemGroup>
+    <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-j3p4-wp97-rph4" />
+    <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-j9gm-c75j-xc9q" />
+    <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-jjfr-hcj7-qf5w" />
+    <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-gwg2-r3hj-4w44" />
+    <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-wmxv-xphr-5c9g" />
+  </ItemGroup>
 </Project>

IconHelper.Test/ProcessDirectoryTests.cs

@@ -166,6 +166,27 @@
 		Assert.IsTrue(File.Exists(Path.Combine(output, "good.png")));
 	}
 
+	[TestMethod]
+	public void SkipsFileManagerMetadataWithoutCountingItAsFailed()
+	{
+		using TempDirectory temp = new();
+		string input = temp.Combine("in");
+		string output = temp.Combine("out");
+		Directory.CreateDirectory(input);
+		File.WriteAllBytes(Path.Join(input, ".DS_Store"), [0, 0, 0, 1, (byte)'B', (byte)'u', (byte)'d', (byte)'1']);
+		File.WriteAllText(Path.Join(input, "._good.png"), "AppleDouble resource fork");
+		File.WriteAllText(Path.Join(input, "desktop.ini"), "[.ShellClassInfo]\r\n");
+		File.WriteAllText(Path.Join(input, "THUMBS.DB"), "not an image");
+		File.WriteAllText(Path.Join(input, "ehthumbs.db"), "not an image");
+		WritePng(Path.Join(input, "good.png"), 64);
+
+		BatchResult result = IconHelper.ProcessDirectory(ArgumentsFor(input, output), NamedColors.White);
+
+		Assert.AreEqual(new BatchResult(1, 0), result, "File-manager metadata should be neither written nor failed.");
+		Assert.AreEqual(IconHelper.ExitSuccess, IconHelper.ExitCodeFor(result));
+		Assert.AreEqual(1, Directory.GetFiles(output).Length);
+	}
+
 	[TestMethod]
 	public void ReportsAndSkipsAFileThatCannotBeOpened()
 	{

IconHelper/IconHelper.cs

@@ -125,7 +125,8 @@ internal static BatchResult ProcessDirectory(Arguments args, Color color)
 			// whole string let a directory anywhere above the input -- a user name, a date stamp,
 			// a project folder -- decide that every file below it was already generated. That
 			// failure is silent and total: nothing is written and the run still exits 0.
-			if (Path.GetFileName(file).Contains(".new.png", StringComparison.Ordinal))
+			string fileName = Path.GetFileName(file);
+			if (fileName.Contains(".new.png", StringComparison.Ordinal) || IsFileManagerMetadata(fileName))
 			{
 				continue;
 			}
@@ -169,6 +170,18 @@ internal static BatchResult ProcessDirectory(Arguments args, Color color)
 		return new BatchResult(processed, failed);
 	}
 
+	/// <summary>
+	/// Names that Finder and Explorer drop into any folder they open: dot-files such as .DS_Store and
+	/// ._ AppleDouble files, plus Thumbs.db, ehthumbs.db and desktop.ini. They are not icons, so they
+	/// count as neither written nor failed; counting them as failures made every batch on such a
+	/// folder exit 2 and taught scripts to ignore the code that reports real decode failures.
+	/// </summary>
+	internal static bool IsFileManagerMetadata(string fileName)
+		=> fileName.StartsWith('.')
+		|| fileName.Equals("Thumbs.db", StringComparison.OrdinalIgnoreCase)
+		|| fileName.Equals("ehthumbs.db", StringComparison.OrdinalIgnoreCase)
+		|| fileName.Equals("desktop.ini", StringComparison.OrdinalIgnoreCase);
+
 	/// <summary>
 	/// Reduces an icon to a coverage mask: every pixel carries the flat target colour and the shape
 	/// lives entirely in the alpha channel. The result is trimmed of its transparent margins, centred