[release-notes] MSBuild in .NET 11 RC 1

release-notes/11.0/preview/rc1/msbuild.md

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+# MSBuild in .NET 11 RC 1 - Release Notes
+
+.NET 11 RC 1 includes new MSBuild features and improvements:
+
+- [Create and extract tar archives](#create-and-extract-tar-archives)
+- [MSBuild server APIs move to a stable namespace](#msbuild-server-apis-move-to-a-stable-namespace)
+- [Breaking changes](#breaking-changes)
+- [Bug fixes](#bug-fixes)
+
+## Create and extract tar archives
+
+MSBuild adds inbox `TarDirectory` and `Untar` tasks for .NET builds
+([dotnet/msbuild #14451](https://github.com/dotnet/msbuild/pull/14451)).
+The tasks are .NET-only because they use `System.Formats.Tar`; they aren't
+available in Visual Studio's .NET Framework `MSBuild.exe`.
+
+`TarDirectory` creates an uncompressed tar archive by default and can create a
+gzip-compressed archive with `Compression="GZip"`:
+
+```xml
+<Target Name="ArchiveOutput" AfterTargets="Publish">
+  <TarDirectory
+      SourceDirectory="$(PublishDir)"
+      DestinationFile="$(ArtifactsPath)\package.tar.gz"
+      Compression="GZip"
+      Overwrite="true" />
+</Target>
+```
+
+It also supports `FailIfNotIncremental`, matching the question-mode behavior
+of the existing archive tasks. An existing destination produces an error unless
+`Overwrite="true"` is set.
+
+`Untar` accepts one or more archives, skips unchanged files by default, and can
+optionally overwrite read-only destination files:
+
+```xml
+<Target Name="ExtractDependencies">
+  <Untar
+      SourceFiles="@(DependencyArchives)"
+      DestinationFolder="$(IntermediateOutputPath)dependencies"
+      SkipUnchangedFiles="true"
+      OverwriteReadOnlyFiles="false" />
+</Target>
+```
+
+## MSBuild server APIs move to a stable namespace
+
+The MSBuild server's public entry points have moved from
+`Microsoft.Build.Experimental` to `Microsoft.Build.Server`
+([dotnet/msbuild #13964](https://github.com/dotnet/msbuild/pull/13964)):
+
+- `MSBuildClient`
+- `MSBuildClientExitResult`
+- `MSBuildClientExitType`
+- `OutOfProcServerNode`, including its `BuildCallback` delegate
+
+Update source imports and rebuild code that consumes these APIs:
+
+```diff
+-using Microsoft.Build.Experimental;
++using Microsoft.Build.Server;
+```
+
+This is a binary-breaking namespace move with no forwarding types. Libraries
+compiled against the experimental namespace must be recompiled.
+
+## Breaking changes
+
+- **XML tasks prohibit document type definitions by default.** `XmlPeek`,
+  `XmlPoke`, and `XslTransformation` now default `ProhibitDtd` to `true` and
+  report a DTD-specific error
+  ([dotnet/msbuild #14285](https://github.com/dotnet/msbuild/pull/14285)).
+  Remove DTDs from build-time XML where possible. For trusted input that still
+  requires one, set `ProhibitDtd="false"` explicitly on the task.
+- **Change waves 17.10, 17.12, 17.14, and 18.3 are retired.** Their newer
+  behaviors are now unconditional
+  ([dotnet/msbuild #14551](https://github.com/dotnet/msbuild/pull/14551)).
+  This only changes builds that opted out through
+  `MSBUILDDISABLEFEATURESFROMVERSION`. A value that names a retired wave is
+  clamped to 18.4 and produces warning MSB4272. Update the build to work with
+  the current behavior instead of depending on the retired opt-out.
+
+<!-- Filtered features (significant engineering work, but too niche for release notes):
+  - Event-level task telemetry: diagnostics plumbing intended for telemetry consumers rather than a general build workflow.
+  - FileAccessData glob-pattern APIs: specialized extensibility for file-access instrumentation.
+  - Directory.Parse.config tolerant parsing: compatibility infrastructure without a broadly applicable project-file feature.
+-->
+
+## Bug fixes
+
+- **MSBuild server**
+  - [Reset process state between server requests](https://github.com/dotnet/msbuild/pull/14475)
+  - [Scope server and coordinator resource names to the current user](https://github.com/dotnet/msbuild/pull/14543)
+  - [Give each transient server its own identity](https://github.com/dotnet/msbuild/pull/14647)
+- **Build engine**
+  - [Fix concurrent BuildCheck callback mutation](https://github.com/dotnet/msbuild/pull/14590)
+  - [Keep projects active through post-build telemetry](https://github.com/dotnet/msbuild/pull/14679)
+  - [Preserve the XML cache after restore reloads it from disk](https://github.com/dotnet/msbuild/pull/14558)
+- **Task host**
+  - [Fix file-access reporting for detoured nodes](https://github.com/dotnet/msbuild/pull/14602)
+  - [Scope .NET task-host handshake leniency to architecture](https://github.com/dotnet/msbuild/pull/14579)