Fix changelog bundle encoding characters

src/services/Elastic.Changelog/Bundling/ChangelogBundlingService.cs

@@ -199,8 +199,8 @@ private async Task WriteBundleFileAsync(Bundle bundledData, string outputPath, C
 			_logger.LogInformation("Output file already exists, using unique filename: {OutputPath}", outputPath);
 		}
 
-		// Write bundled file
-		await _fileSystem.File.WriteAllTextAsync(outputPath, bundledYaml, ctx);
+		// Write bundled file with explicit UTF-8 encoding to ensure proper character handling
+		await _fileSystem.File.WriteAllTextAsync(outputPath, bundledYaml, Encoding.UTF8, ctx);
 		_logger.LogInformation("Created bundled changelog: {OutputPath}", outputPath);
 	}
 

src/services/Elastic.Changelog/Creation/ChangelogFileWriter.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information
 
 using System.IO.Abstractions;
+using System.Text;
 using Elastic.Changelog.Configuration;
 using Elastic.Changelog.Serialization;
 using Elastic.Documentation;
@@ -43,8 +44,8 @@ public async Task<bool> WriteChangelogAsync(
 		var filename = GenerateFilename(collector, input, prUrl);
 		var filePath = fileSystem.Path.Combine(outputDir, filename);
 
-		// Write file
-		await fileSystem.File.WriteAllTextAsync(filePath, yamlContent, ctx);
+		// Write file with explicit UTF-8 encoding to ensure proper character handling
+		await fileSystem.File.WriteAllTextAsync(filePath, yamlContent, Encoding.UTF8, ctx);
 		logger.LogInformation("Created changelog fragment: {FilePath}", filePath);
 
 		return true;

src/services/Elastic.Changelog/GithubRelease/GitHubReleaseChangelogService.cs

@@ -273,7 +273,7 @@ private async Task<bool> ProcessPrReference(
 		var slug = ChangelogTextUtilities.GenerateSlug(title);
 		var filename = $"{prRef.PrNumber}-{finalType.ToStringFast(true)}-{slug}.yaml";
 		var filePath = _fileSystem.Path.Combine(outputDir, filename);
-		await _fileSystem.File.WriteAllTextAsync(filePath, yamlContent, ctx);
+		await _fileSystem.File.WriteAllTextAsync(filePath, yamlContent, Encoding.UTF8, ctx);
 
 		createdFiles.Add(filename);
 		_logger.LogDebug("Created changelog: {FilePath}", filePath);
@@ -324,7 +324,7 @@ private async Task<string> CreateBundleFile(
 		// Name format: <version>-<product>-bundle.yml
 		var bundleFilename = $"{productInfo.Target}-{productInfo.Product}-bundle.yml";
 		var bundlePath = _fileSystem.Path.Combine(bundlesDir, bundleFilename);
-		await _fileSystem.File.WriteAllTextAsync(bundlePath, yamlContent, ctx);
+		await _fileSystem.File.WriteAllTextAsync(bundlePath, yamlContent, Encoding.UTF8, ctx);
 
 		return bundlePath;
 	}

src/services/Elastic.Changelog/Rendering/Asciidoc/ChangelogAsciidocRenderer.cs

@@ -123,7 +123,7 @@ public async Task RenderAsciidoc(ChangelogRenderContext context, Cancel ctx)
 		if (!string.IsNullOrWhiteSpace(asciidocDir) && !fileSystem.Directory.Exists(asciidocDir))
 			_ = fileSystem.Directory.CreateDirectory(asciidocDir);
 
-		await fileSystem.File.WriteAllTextAsync(asciidocPath, sb.ToString(), ctx);
+		await fileSystem.File.WriteAllTextAsync(asciidocPath, sb.ToString(), Encoding.UTF8, ctx);
 	}
 
 	private static void RenderSectionHeader(StringBuilder sb, string anchorPrefix, string titleSlug, string title)

src/services/Elastic.Changelog/Rendering/Markdown/MarkdownRendererBase.cs

@@ -31,7 +31,7 @@ protected async Task WriteOutputFileAsync(string outputDir, string titleSlug, st
 		if (!string.IsNullOrWhiteSpace(outputDirectory) && !FileSystem.Directory.Exists(outputDirectory))
 			_ = FileSystem.Directory.CreateDirectory(outputDirectory);
 
-		await FileSystem.File.WriteAllTextAsync(outputPath, content, ctx);
+		await FileSystem.File.WriteAllTextAsync(outputPath, content, Encoding.UTF8, ctx);
 	}
 
 	/// <summary>

src/services/Elastic.Changelog/Serialization/ChangelogYamlSerialization.cs

@@ -35,6 +35,8 @@ public static class ChangelogYamlSerialization
 		new StaticSerializerBuilder(new ChangelogYamlStaticContext())
 			.WithNamingConvention(UnderscoredNamingConvention.Instance)
 			.ConfigureDefaultValuesHandling(DefaultValuesHandling.OmitNull | DefaultValuesHandling.OmitEmptyCollections)
+			.WithQuotingNecessaryStrings()
+			.DisableAliases()
 			.Build();
 
 	/// <summary>

tests/Elastic.Changelog.Tests/Changelogs/BundleChangelogsTests.cs

@@ -1292,6 +1292,93 @@ public async Task BundleChangelogs_WithResolve_CopiesChangelogContents()
 		bundleContent.Should().Contain("description: This is a test feature");
 	}
 
+	[Fact]
+	public async Task BundleChangelogs_WithResolve_PreservesSpecialCharactersInUtf8()
+	{
+		// Arrange - Create changelog with special characters that could be corrupted
+		// These characters were reported as being corrupted to "&o0" and "*o0" in the original issue
+
+		// language=yaml
+		var changelog1 =
+			"""
+			title: Feature with special characters & symbols
+			type: feature
+			products:
+			  - product: elasticsearch
+			    target: 9.3.0
+			    lifecycle: ga
+			pr: https://github.com/elastic/elasticsearch/pull/100
+			description: |
+			  This feature includes special characters:
+			  - Ampersand: & symbol
+			  - Asterisk: * symbol
+			  - Other special chars: < > " ' / \
+			  - Unicode: © ® ™ € £ ¥
+			""";
+
+		var file1 = FileSystem.Path.Combine(_changelogDir, "1755268130-special-chars.yaml");
+		await FileSystem.File.WriteAllTextAsync(file1, changelog1, System.Text.Encoding.UTF8, TestContext.Current.CancellationToken);
+
+		var outputPath = FileSystem.Path.Combine(FileSystem.Path.GetTempPath(), Guid.NewGuid().ToString(), "bundle.yaml");
+		var input = new BundleChangelogsArguments
+		{
+			Directory = _changelogDir,
+			All = true,
+			Resolve = true,
+			Output = outputPath
+		};
+
+		// Act
+		var result = await Service.BundleChangelogs(Collector, input, TestContext.Current.CancellationToken);
+
+		// Assert
+		result.Should().BeTrue();
+		Collector.Errors.Should().Be(0);
+
+		// Read the bundle file with explicit UTF-8 encoding
+		var bundleContent = await FileSystem.File.ReadAllTextAsync(input.Output, System.Text.Encoding.UTF8, TestContext.Current.CancellationToken);
+
+		// Verify special characters are preserved correctly (not corrupted)
+		// The original issue reported "&o0" and "*o0" corruption, so we verify the characters are correct
+		bundleContent.Should().Contain("&"); // Ampersand should be preserved
+		bundleContent.Should().Contain("Feature with special characters & symbols"); // Ampersand in title
+		bundleContent.Should().Contain("Ampersand: & symbol"); // Ampersand in description
+
+		// Check that asterisk appears correctly (not corrupted to "*o0")
+		bundleContent.Should().Contain("*"); // Asterisk should be preserved
+		bundleContent.Should().Contain("Asterisk: * symbol"); // Asterisk in description
+
+		// Verify the ampersand and asterisk are not corrupted
+		// The corruption pattern would be "&o0" or "*o0" appearing where we expect "&" or "*"
+		// We check that the title contains the correct pattern, not the corrupted one
+		var titleLine = bundleContent.Split('\n').FirstOrDefault(l => l.Contains("title:"));
+		titleLine.Should().NotBeNull();
+		titleLine.Should().Contain("&");
+		titleLine.Should().NotContain("&o0"); // Should not be corrupted in title
+
+		// Verify no corruption patterns exist (these would indicate encoding issues)
+		bundleContent.Should().NotContain("&o0"); // Should not contain corrupted ampersand
+		bundleContent.Should().NotContain("*o0"); // Should not contain corrupted asterisk
+
+		// Verify other special characters are preserved
+		bundleContent.Should().Contain("<");
+		bundleContent.Should().Contain(">");
+		bundleContent.Should().Contain("\"");
+
+		// Verify Unicode characters are preserved
+		bundleContent.Should().Contain("©");
+		bundleContent.Should().Contain("®");
+		bundleContent.Should().Contain("™");
+		bundleContent.Should().Contain("€");
+
+		// Verify the content structure is correct
+		bundleContent.Should().Contain("title: Feature with special characters & symbols");
+		bundleContent.Should().Contain("type: feature");
+		bundleContent.Should().Contain("product: elasticsearch");
+		bundleContent.Should().Contain("target: 9.3.0");
+		bundleContent.Should().Contain("lifecycle: ga");
+	}
+
 	[Fact]
 	public async Task BundleChangelogs_WithDirectoryOutputPath_CreatesDefaultFilename()
 	{