Fix FileSystem rights requested for writing changelogs (#3055)

* Fix FileSystem rights requested for writing changelogs

* Fix tests

Author: cotti

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

@@ -74,7 +74,7 @@ public class ChangelogCreationService(
 	private readonly CreateChangelogArgumentsValidator _validator = new(configurationContext);
 	private readonly PrInfoProcessor _prProcessor = new(githubPrService, logFactory.CreateLogger<PrInfoProcessor>());
 	private readonly IssueInfoProcessor _issueProcessor = new(githubPrService, logFactory.CreateLogger<IssueInfoProcessor>());
-	private readonly ChangelogFileWriter _fileWriter = new(fileSystem ?? FileSystemFactory.RealRead, logFactory.CreateLogger<ChangelogFileWriter>());
+	private readonly ChangelogFileWriter _fileWriter = new(fileSystem ?? FileSystemFactory.RealWrite, logFactory.CreateLogger<ChangelogFileWriter>());
 	private readonly ProductInferService _productInferService = new(
 		configurationContext.ProductsConfiguration);
 

tests/Elastic.Changelog.Tests/Creation/ChangelogCreationServiceTests.cs

@@ -2,6 +2,7 @@
 // Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information
 
+using System.IO.Abstractions.TestingHelpers;
 using AwesomeAssertions;
 using Elastic.Changelog.Creation;
 using Elastic.Changelog.GitHub;
@@ -183,4 +184,50 @@ public async Task CreateChangelog_CIWithoutProducts_NoPrProductLabels_FailsWithP
 		Collector.Errors.Should().Be(1);
 		Collector.Diagnostics.Should().Contain(d => d.Message.Contains("At least one product is required"));
 	}
+
+	/// <summary>
+	/// When --output points to a temp directory (e.g. /tmp/changelog-staging in CI),
+	/// the service must use a write-scoped filesystem that allows temp paths.
+	/// Regression test for ScopedFileSystemException on temp output.
+	/// </summary>
+	[Fact]
+	public async Task CreateChangelog_TempOutputDirectory_Succeeds()
+	{
+		var mockFs = new MockFileSystem(new MockFileSystemOptions { CurrentDirectory = Paths.WorkingDirectoryRoot.FullName });
+		var writeFs = FileSystemFactory.ScopeCurrentWorkingDirectoryForWrite(mockFs);
+
+		var configPath = Path.Join(Paths.WorkingDirectoryRoot.FullName, "config", "changelog.yml");
+		writeFs.Directory.CreateDirectory(writeFs.Path.GetDirectoryName(configPath)!);
+		await writeFs.File.WriteAllTextAsync(configPath, ConfigWithProductLabels, TestContext.Current.CancellationToken);
+
+		// Use the real system temp path so AllowedSpecialFolder.Temp matches cross-platform.
+		// MockFileSystem's GetTempPath() returns a hardcoded "C:\temp" that diverges from the
+		// real temp on Windows CI (D:\Temp), causing scope validation to fail.
+		var tempOutput = Path.Join(Path.GetTempPath(), "changelog-staging");
+
+		var env = FakeCIEnv(
+			prNumber: "1044",
+			title: "move upstream update script to .ci",
+			type: "bug-fix",
+			owner: "elastic",
+			repo: "elastic-otel-java",
+			products: "elasticsearch"
+		);
+
+		var service = new ChangelogCreationService(LoggerFactory, ConfigurationContext, _mockGitHub, writeFs, env);
+		var input = new CreateChangelogArguments
+		{
+			Products = [],
+			Config = configPath,
+			Output = tempOutput,
+			Concise = true
+		};
+
+		var result = await service.CreateChangelog(Collector, input, TestContext.Current.CancellationToken);
+
+		result.Should().BeTrue();
+		Collector.Errors.Should().Be(0);
+		writeFs.Directory.Exists(tempOutput).Should().BeTrue();
+		writeFs.Directory.GetFiles(tempOutput, "*.yaml").Should().NotBeEmpty();
+	}
 }