Refactor: use TaskEnvironment public API

.github/skills/multithreaded-task-migration/SKILL.md

@@ -18,7 +18,7 @@ b. Implement `IMultiThreadableTask` **only if** the task needs `TaskEnvironment`
 [MSBuildMultiThreadableTask]
 public class MyTask : Task, IMultiThreadableTask
 {
-    public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+    public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
     ...
 }
 ```
@@ -276,7 +276,7 @@ Assertions: Execute() return value, [Output] exact string, error message content
 ## Sign-Off Checklist
 
 - [ ] `[MSBuildMultiThreadableTask]` on every concrete class (not just base — `Inherited=false`)
-- [ ] `IMultiThreadableTask` on classes that use `TaskEnvironment` APIs, with default initializer `= new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance)`
+- [ ] `IMultiThreadableTask` on classes that use `TaskEnvironment` APIs, with default initializer `= TaskEnvironment.Fallback`
 - [ ] Every `[Output]` property: exact string value matches pre-migration
 - [ ] Every `Log.LogError`/`LogWarning`: path in message matches pre-migration (use `OriginalValue`)
 - [ ] Every `GetAbsolutePath` call: null/empty exception behavior matches old code path

documentation/specs/multithreading/thread-safe-tasks.md

@@ -39,7 +39,7 @@ Similar to how MSBuild provides the abstract `Task` class with default implement
 namespace Microsoft.Build.Utilities;
 public abstract class MultiThreadableTask : Task, IMultiThreadableTask
 {
-    public TaskEnvironment TaskEnvironment{ get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+    public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 }
 ```
 

src/Build.UnitTests/BackEnd/TaskEnvironment_Tests.cs

@@ -31,8 +31,8 @@ private static TaskEnvironment CreateTaskEnvironment(string environmentType)
         {
             return environmentType switch
             {
-                StubEnvironmentName => TaskEnvironmentHelper.CreateForTest(),
-                MultithreadedEnvironmentName => new TaskEnvironment(new MultiThreadedTaskEnvironmentDriver(GetResolvedTempPath())),
+                StubEnvironmentName => TaskEnvironment.Fallback,
+                MultithreadedEnvironmentName => TaskEnvironment.CreateWithProjectDirectoryAndEnvironment(GetResolvedTempPath()),
                 _ => throw new ArgumentException($"Unknown environment type: {environmentType}")
             };
         }
@@ -306,7 +306,7 @@ public void TaskEnvironment_StubEnvironment_ShouldAffectSystemEnvironment()
             string testVarName = $"MSBUILD_STUB_ISOLATION_TEST_{Guid.NewGuid():N}";
             string testVarValue = "stub_test_value";
 
-            var stubEnvironment = TaskEnvironmentHelper.CreateForTest();
+            var stubEnvironment = TaskEnvironment.Fallback;
 
             try
             {
@@ -336,10 +336,9 @@ public void TaskEnvironment_MultithreadedEnvironment_ShouldBeIsolatedFromSystem(
             string testVarName = $"MSBUILD_MULTITHREADED_ISOLATION_TEST_{Guid.NewGuid():N}";
             string testVarValue = "multithreaded_test_value";
 
-            using var driver = new MultiThreadedTaskEnvironmentDriver(
+            var multithreadedEnvironment = TaskEnvironment.CreateWithProjectDirectoryAndEnvironment(
                 GetResolvedTempPath(),
                 new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase));
-            var multithreadedEnvironment = new TaskEnvironment(driver);
 
             try
             {

src/Build/BackEnd/Components/BuildRequestEngine/BuildRequestEngine.cs

@@ -394,11 +394,11 @@ public void SubmitBuildRequest(BuildRequest request)
                         {
                             string projectDirectoryFullPath = Path.GetDirectoryName(config.ProjectFullPath);
                             var environmentVariables = new Dictionary<string, string>(_componentHost.BuildParameters.BuildProcessEnvironmentInternal);
-                            taskEnvironment = new TaskEnvironment(new MultiThreadedTaskEnvironmentDriver(projectDirectoryFullPath, environmentVariables));
+                            taskEnvironment = TaskEnvironment.CreateWithProjectDirectoryAndEnvironment(projectDirectoryFullPath, environmentVariables);
                         }
                         else
                         {
-                            taskEnvironment = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+                            taskEnvironment = TaskEnvironment.Fallback;
                         }
 
                         BuildRequestEntry entry = new BuildRequestEntry(request, config, taskEnvironment);

src/Tasks/AssignTargetPath.cs

@@ -23,7 +23,7 @@ public class AssignTargetPath : TaskExtension, IMultiThreadableTask
         /// <summary>
         /// Gets or sets the task execution environment for thread-safe path resolution.
         /// </summary>
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
 
         /// <summary>

src/Tasks/Copy.cs

@@ -187,7 +187,7 @@ public Copy()
         public bool FailIfNotIncremental { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         #endregion
 

src/Tasks/Delete.cs

@@ -65,7 +65,7 @@ public ITaskItem[] Files
         public bool FailIfNotIncremental { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// Verify that the inputs are correct.

src/Tasks/DownloadFile.cs

@@ -69,7 +69,7 @@ public sealed class DownloadFile : TaskExtension, ICancelableTask, IIncrementalT
         public bool FailIfNotIncremental { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// Gets or sets a <see cref="HttpMessageHandler"/> to use.  This is used by unit tests to mock a connection to a remote server.

src/Tasks/FileIO/GetFileHash.cs

@@ -66,7 +66,7 @@ internal static readonly Dictionary<string, Func<HashAlgorithm>> SupportedAlgori
         public ITaskItem[] Items { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         public override bool Execute()
         {

src/Tasks/FileIO/ReadLinesFromFile.cs

@@ -25,7 +25,7 @@ public class ReadLinesFromFile : TaskExtension, IMultiThreadableTask
         public ITaskItem File { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// Receives lines from file.

src/Tasks/FileIO/VerifyFileHash.cs

@@ -17,7 +17,7 @@ namespace Microsoft.Build.Tasks
     public sealed class VerifyFileHash : TaskExtension, ICancelableTask, IMultiThreadableTask
     {
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// The file path.

src/Tasks/FileIO/WriteLinesToFile.cs

@@ -23,7 +23,7 @@ public class WriteLinesToFile : TaskExtension, IIncrementalTask, IMultiThreadabl
         private static readonly Encoding s_defaultEncoding = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false, throwOnInvalidBytes: true);
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// File to write lines to.

src/Tasks/ListOperators/FindUnderPath.cs

@@ -21,7 +21,7 @@ public class FindUnderPath : TaskExtension, IMultiThreadableTask
         /// <summary>
         /// Gets or sets the task execution environment for thread-safe path resolution.
         /// </summary>
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// Filter based on whether items fall under this path or not.

src/Tasks/MakeDir.cs

@@ -35,7 +35,7 @@ public ITaskItem[] Directories
         public bool FailIfNotIncremental { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         private ITaskItem[] _directories;
 

src/Tasks/Move.cs

@@ -76,7 +76,7 @@ public class Move : TaskExtension, ICancelableTask, IIncrementalTask, IMultiThre
         public bool FailIfNotIncremental { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// Stop and return (in an undefined state) as soon as possible.

src/Tasks/RemoveDir.cs

@@ -25,7 +25,7 @@ public class RemoveDir : TaskExtension, IIncrementalTask, IMultiThreadableTask
         private ITaskItem[] _directories;
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         [Required]
         public ITaskItem[] Directories

src/Tasks/Touch.cs

@@ -50,7 +50,7 @@ public class Touch : TaskExtension, IIncrementalTask, IMultiThreadableTask
         public ITaskItem[] TouchedFiles { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// Importance: high, normal, low (default normal)

src/Tasks/Unzip.cs

@@ -77,7 +77,7 @@ public sealed class Unzip : TaskExtension, ICancelableTask, IIncrementalTask, IM
         public bool FailIfNotIncremental { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <inheritdoc cref="ICancelableTask.Cancel"/>
         public void Cancel()

src/Tasks/WriteCodeFragment.cs

@@ -34,7 +34,7 @@ namespace Microsoft.Build.Tasks
     public class WriteCodeFragment : TaskExtension, IMultiThreadableTask
     {
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
         private const string TypeNameSuffix = "_TypeName";
         private const string IsLiteralSuffix = "_IsLiteral";
         private static readonly string[] NamespaceImports = ["System", "System.Reflection"];

src/Tasks/XmlPeek.cs

@@ -25,7 +25,7 @@ public class XmlPeek : TaskExtension, IMultiThreadableTask
         #region Properties
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// The XPath Query.

src/Tasks/XmlPoke.cs

@@ -24,7 +24,7 @@ public class XmlPoke : TaskExtension, IMultiThreadableTask
         #region Properties
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// The XML input as file path.

src/Tasks/XslTransformation.cs

@@ -29,7 +29,7 @@ public class XslTransformation : TaskExtension, IMultiThreadableTask
         #region Members
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         /// <summary>
         /// The output files.

src/Tasks/ZipDirectory.cs

@@ -59,7 +59,7 @@ public sealed class ZipDirectory : TaskExtension, IIncrementalTask, IMultiThread
         public string? CompressionLevel { get; set; }
 
         /// <inheritdoc />
-        public TaskEnvironment TaskEnvironment { get; set; } = new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+        public TaskEnvironment TaskEnvironment { get; set; } = TaskEnvironment.Fallback;
 
         public override bool Execute()
         {

src/UnitTests.Shared/TaskEnvironmentHelper.cs

@@ -18,7 +18,7 @@ public static class TaskEnvironmentHelper
         /// <returns>A TaskEnvironment suitable for use in tests.</returns>
         public static TaskEnvironment CreateForTest()
         {
-            return new TaskEnvironment(MultiProcessTaskEnvironmentDriver.Instance);
+            return TaskEnvironment.Fallback;
         }
     }
 }