From 13c986f62ce79713df482f6af0c65c8fa7172f8c Mon Sep 17 00:00:00 2001
From: pavelsavara <pavel.savara@gmail.com>
Date: Fri, 14 Aug 2026 21:01:34 +0200
Subject: [PATCH 1/3] Enable crossgen2 to target browser-wasm/wasi-wasm

ResolveReadyToRunCompilers: add wasm architecture and browser/wasi OS so the SDK can resolve the crossgen2 pack for wasm. Dual-install clrjit_universal_wasm_* into the alljits component so the shipped Microsoft.NETCore.App.Crossgen2.<hostRID> pack carries the wasm cross-JIT (crossgen2 v6+ auto-loads it from tools/).

Assisted-by: GitHub Copilot
---
 src/coreclr/jit/CMakeLists.txt                         |  2 +-
 src/tasks/Crossgen2Tasks/ResolveReadyToRunCompilers.cs | 10 +++++++++-
 src/tasks/Crossgen2Tasks/RunReadyToRunCompiler.cs      |  1 +
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/coreclr/jit/CMakeLists.txt b/src/coreclr/jit/CMakeLists.txt
index 7e9791ebe60adb..3999593c2bbca1 100644
--- a/src/coreclr/jit/CMakeLists.txt
+++ b/src/coreclr/jit/CMakeLists.txt
@@ -697,7 +697,7 @@ function(add_jit jitName)
 
     # add the install targets
     if (${jitName} MATCHES "clrjit_universal_wasm")
-        # TODO-WASM: add the WASM Jit to alljits once that becomes necessary.
+        install_clr(TARGETS ${jitName} DESTINATIONS . COMPONENT alljits)
         install_clr(TARGETS ${jitName} DESTINATIONS . COMPONENT wasmjit)
     else()
         install_clr(TARGETS ${jitName} DESTINATIONS . COMPONENT alljits)
diff --git a/src/tasks/Crossgen2Tasks/ResolveReadyToRunCompilers.cs b/src/tasks/Crossgen2Tasks/ResolveReadyToRunCompilers.cs
index d487eb995a396b..684d1d84639c97 100644
--- a/src/tasks/Crossgen2Tasks/ResolveReadyToRunCompilers.cs
+++ b/src/tasks/Crossgen2Tasks/ResolveReadyToRunCompilers.cs
@@ -210,7 +210,7 @@ private bool GetCrossgen2TargetOS(out string targetOS)
             string portablePlatform = NuGetUtils.GetBestMatchingRid(
                     runtimeGraph,
                     _targetRuntimeIdentifier,
-                    new[] { "linux", "android", "osx", "win", "freebsd", "illumos" },
+                    new[] { "linux", "android", "osx", "win", "freebsd", "illumos", "browser", "wasi" },
                     out _);
 
             targetOS = portablePlatform switch
@@ -221,6 +221,8 @@ private bool GetCrossgen2TargetOS(out string targetOS)
                 "win" => "windows",
                 "freebsd" => "freebsd",
                 "illumos" => "illumos",
+                "browser" => "browser",
+                "wasi" => "wasi",
                 _ => null
             };
 
@@ -280,6 +282,11 @@ private static bool ExtractTargetPlatformAndArchitecture(string runtimeIdentifie
                 case "x86":
                     architecture = Architecture.X86;
                     break;
+#if !NETFRAMEWORK
+                case "wasm":
+                    architecture = Architecture.Wasm;
+                    break;
+#endif
                 default:
                     return false;
             }
@@ -444,6 +451,7 @@ private static string ArchitectureToString(Architecture architecture)
 #if !NETFRAMEWORK
                 Architecture.RiscV64 => "riscv64",
                 Architecture.LoongArch64 => "loongarch64",
+                Architecture.Wasm => "wasm",
 #endif
                 _ => null
             };
diff --git a/src/tasks/Crossgen2Tasks/RunReadyToRunCompiler.cs b/src/tasks/Crossgen2Tasks/RunReadyToRunCompiler.cs
index 22045ddd145fdf..ed514da93a8eaf 100644
--- a/src/tasks/Crossgen2Tasks/RunReadyToRunCompiler.cs
+++ b/src/tasks/Crossgen2Tasks/RunReadyToRunCompiler.cs
@@ -23,6 +23,7 @@ public class RunReadyToRunCompiler : ToolTask
         public bool ShowCompilerWarnings { get; set; }
         public bool UseCrossgen2 { get; set; }
         public string Crossgen2ExtraCommandLineArgs { get; set; }
+        public string Crossgen2CompositeExtraCommandLineArgs { get; set; }
         public ITaskItem[] Crossgen2PgoFiles { get; set; }
         public string Crossgen2ContainerFormat { get; set; }
 

From 23f07753ac796ba499a602141c6ab03fa8e5edec Mon Sep 17 00:00:00 2001
From: pavelsavara <pavel.savara@gmail.com>
Date: Fri, 14 Aug 2026 21:01:41 +0200
Subject: [PATCH 2/3] Ship prebuilt framework ReadyToRun images in the
 browser-wasm runtime pack

Crossgen each shared-framework assembly to a webcil-in-wasm R2R image under runtimes/browser-wasm/native/r2r/, keeping the IL in lib/ (the CoreLib model generalized to the whole framework). CoreLib.wasm comes from the coreclr build. WasmFrameworkR2RSubset limits the set for bring-up. Nothing consumes these yet; the SDK integration is a follow-up commit. See dotnet/runtime#121257.

Assisted-by: GitHub Copilot
---
 ...rosoft.NETCore.App.Runtime.CoreCLR.sfxproj | 65 ++++++++++++++++++-
 1 file changed, 64 insertions(+), 1 deletion(-)

diff --git a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.CoreCLR.sfxproj b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.CoreCLR.sfxproj
index 45a5d877f608a9..a78066f5fdb16a 100644
--- a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.CoreCLR.sfxproj
+++ b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.CoreCLR.sfxproj
@@ -26,7 +26,8 @@
     <PublishReadyToRun>true</PublishReadyToRun>
     <!-- Disable crossgen on NetBSD, illumos, Solaris and Haiku for now. This can be revisited when we have full support. -->
     <PublishReadyToRun Condition="'$(TargetOS)' == 'netbsd' or '$(TargetOS)' == 'illumos' or '$(TargetOS)' == 'solaris' or '$(TargetOS)' == 'haiku'">false</PublishReadyToRun>
-    <!-- TODO-WASM: we will have WASM R2R after https://github.com/dotnet/runtime/issues/121257 -->
+    <!-- TODO-WASM: WASM framework R2R needs the CoreLib model (native/*.wasm webcil + kept lib/*.dll IL),
+         not the SDK's in-place R2R which replaces lib/*.dll. See dotnet/runtime#121257. -->
     <PublishReadyToRun Condition="'$(TargetOS)' == 'browser' or '$(TargetOS)' == 'wasi'">false</PublishReadyToRun>
     <PublishReadyToRun Condition="'$(StageTwoBuild)'=='true'">false</PublishReadyToRun>
     <UsesMuxerHostModel Condition="'$(TargetsMobile)' != 'true'">true</UsesMuxerHostModel>
@@ -64,6 +65,68 @@
     </PropertyGroup>
   </Target>
 
+  <!--
+    WASM framework R2R: crossgen each shared-framework assembly to a webcil-in-wasm R2R image under the
+    pack native/r2r/, keeping the IL in lib/ (the CoreLib model generalized; the SDK's in-place R2R can't
+    be used as it drops the IL). See PR.md / dotnet/runtime#121257. WasmFrameworkR2RSubset limits the set.
+  -->
+  <PropertyGroup Condition="'$(TargetsBrowser)' == 'true' and '$(RuntimeFlavor)' == 'CoreCLR'">
+    <WasmEnableFrameworkR2R Condition="'$(WasmEnableFrameworkR2R)' == ''">true</WasmEnableFrameworkR2R>
+    <_WasmFrameworkR2RDir>$([MSBuild]::NormalizeDirectory('$(IntermediateOutputPath)', 'framework-r2r'))</_WasmFrameworkR2RDir>
+  </PropertyGroup>
+
+  <Target Name="_ComputeBrowserFrameworkR2RInputs"
+          Condition="'$(WasmEnableFrameworkR2R)' == 'true'"
+          DependsOnTargets="ResolveLibrariesFromLocalBuild;ResolveRuntimeFilesFromLocalBuild">
+    <ItemGroup>
+      <_WasmFrameworkR2RInput Include="$(LibrariesSharedFrameworkBinArtifactsPath)*.dll"
+                              Exclude="$(LibrariesSharedFrameworkBinArtifactsPath)*.resources.dll" />
+      <!-- Optional subset filter for bring-up: keep only assemblies named in WasmFrameworkR2RSubset. -->
+      <_WasmFrameworkR2RInput Remove="@(_WasmFrameworkR2RInput)"
+                              Condition="'$(WasmFrameworkR2RSubset)' != '' and !$([System.String]::Copy(';$(WasmFrameworkR2RSubset);').Contains(';%(FileName);'))" />
+      <_WasmFrameworkR2RInput>
+        <OutputWasm>$(_WasmFrameworkR2RDir)%(FileName).wasm</OutputWasm>
+      </_WasmFrameworkR2RInput>
+    </ItemGroup>
+    <PropertyGroup>
+      <_WasmCoreLibIL Condition="Exists('$(CoreCLRArtifactsPath)System.Private.CoreLib.dll')">$(CoreCLRArtifactsPath)System.Private.CoreLib.dll</_WasmCoreLibIL>
+      <_WasmCoreLibIL Condition="'$(_WasmCoreLibIL)' == '' and Exists('$(CoreCLRArtifactsPath)IL\System.Private.CoreLib.dll')">$(CoreCLRArtifactsPath)IL\System.Private.CoreLib.dll</_WasmCoreLibIL>
+      <_WasmCrossgen2Exe>$([MSBuild]::NormalizePath('$(Crossgen2InBuildDir)', 'crossgen2$(ExeSuffix)'))</_WasmCrossgen2Exe>
+    </PropertyGroup>
+  </Target>
+
+  <Target Name="_CrossgenBrowserFrameworkR2R"
+          Condition="'$(WasmEnableFrameworkR2R)' == 'true'"
+          DependsOnTargets="_ComputeBrowserFrameworkR2RInputs"
+          Inputs="@(_WasmFrameworkR2RInput);$(_WasmCoreLibIL)"
+          Outputs="@(_WasmFrameworkR2RInput->'%(OutputWasm)')">
+    <MakeDir Directories="$(_WasmFrameworkR2RDir)" />
+    <Message Importance="High" Text="Crossgen R2R (wasm): %(_WasmFrameworkR2RInput.FileName)" />
+    <Exec Condition="Exists('$(_WasmCrossgen2Exe)')"
+          Command="&quot;$(_WasmCrossgen2Exe)&quot; -o:&quot;%(_WasmFrameworkR2RInput.OutputWasm)&quot; -r:&quot;$(LibrariesSharedFrameworkBinArtifactsPath)*.dll&quot; -r:&quot;$(_WasmCoreLibIL)&quot; --targetarch:$(TargetArchitecture) --targetos:$(TargetOS) --obj-format:wasm --codegenopt:JitWasmNyiToR2RUnsupported=1 --codegenopt:JitWasmSimdNyiToR2RUnsupported=1 -O &quot;%(_WasmFrameworkR2RInput.FullPath)&quot;" />
+  </Target>
+
+  <!-- No Inputs/Outputs so images are packed even when crossgen was incrementally skipped. native/r2r is a
+       dedicated subfolder (no collision with dotnet.native.wasm / served webcils). CoreLib.wasm comes from
+       the coreclr build (crossgen-corelib), not this loop. -->
+  <Target Name="_AddBrowserFrameworkR2RToPackage"
+          Condition="'$(WasmEnableFrameworkR2R)' == 'true'"
+          DependsOnTargets="_CrossgenBrowserFrameworkR2R"
+          BeforeTargets="AddFrameworkFilesToPackage">
+    <ItemGroup>
+      <_WasmFrameworkR2ROutput Include="$(_WasmFrameworkR2RDir)*.wasm" />
+      <_WasmFrameworkR2ROutput Include="$(CoreCLRArtifactsPath)System.Private.CoreLib.wasm"
+                               Condition="Exists('$(CoreCLRArtifactsPath)System.Private.CoreLib.wasm')" />
+      <LibrariesRuntimeFiles Include="@(_WasmFrameworkR2ROutput)" IsNative="true" NativeSubDirectory="r2r" />
+      <PlatformManifestFileEntry Include="@(_WasmFrameworkR2ROutput->'%(FileName)%(Extension)')" IsNative="true" />
+    </ItemGroup>
+    <!-- In-tree runtime-pack layout is assembled by binplace + libs.pretest (not the nupkg), so copy in explicitly. -->
+    <Copy Condition="'$(MicrosoftNetCoreAppRuntimePackNativeDir)' != '' and '@(_WasmFrameworkR2ROutput)' != ''"
+          SourceFiles="@(_WasmFrameworkR2ROutput)"
+          DestinationFolder="$([MSBuild]::NormalizeDirectory('$(MicrosoftNetCoreAppRuntimePackNativeDir)', 'r2r'))"
+          SkipUnchangedFiles="true" />
+  </Target>
+
   <!--
     Put the mibc file into tools and not into PgoData. Add it after GetFilesToPackage to ensure it isn't automatically classified.
     Putting it in tools will also hide it from being part of the RuntimeList.xml.

From 14463db2a94aa2de00e1b8c144e560ead88eeb6d Mon Sep 17 00:00:00 2001
From: pavelsavara <pavel.savara@gmail.com>
Date: Fri, 14 Aug 2026 21:01:55 +0200
Subject: [PATCH 3/3] Consume ReadyToRun images in the browser-wasm CoreCLR app
 build and publish

ConvertDllsToWebcil gains PrebuiltR2RDirectories to stage prebuilt/per-app R2R webcils in place of IL. New Browser.CoreCLR.targets (imported only for UseMonoRuntime=false) defaults R2R on, forces wasm container format + non-composite, prunes raw pack images, feeds the trimmed closure to crossgen2, and orders R2R before the wasm publish. In-tree hooks override ResolveReadyToRunCompilers to the in-build crossgen2. Design and SWA-vs-iOS notes in PR.md.

Assisted-by: GitHub Copilot
---
 .../build/BrowserWasmApp.CoreCLR.targets      |  9 ++
 src/mono/browser/build/WasmApp.InTree.props   |  9 ++
 .../browser/build/WasmApp.ReadyToRun.targets  | 18 ++++
 ...ET.Sdk.WebAssembly.Browser.CoreCLR.targets | 95 +++++++++++++++++++
 ...rosoft.NET.Sdk.WebAssembly.Browser.targets |  8 +-
 .../Wasm.Advanced.Sample.csproj               |  1 +
 .../Wasm.Console.Node.Sample.csproj           |  1 +
 .../ConvertDllsToWebCil.cs                    | 32 +++++++
 8 files changed, 171 insertions(+), 2 deletions(-)
 create mode 100644 src/mono/browser/build/WasmApp.ReadyToRun.targets
 create mode 100644 src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index 0e8b915873fa2d..045ff0d8e04038 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -623,6 +623,15 @@
       <_WasmManagedAssemblies Include="@(WasmAssembliesToBundle->Distinct())" />
     </ItemGroup>
 
+    <!-- With R2R the published .dll are webcil-in-wasm images MetadataLoadContext can't parse; scan the
+         trimmed IL (same closure crossgen used) instead. Gated on the linker dir only, because the nested
+         WasmNestedPublishApp build where this runs doesn't carry PublishReadyToRun. -->
+    <ItemGroup Condition="'$(IntermediateLinkDir)' != ''">
+      <_WasmManagedAssembliesR2RRemap Include="@(_WasmManagedAssemblies)" Condition="Exists('$(IntermediateLinkDir)%(FileName)%(Extension)')" />
+      <_WasmManagedAssemblies Remove="@(_WasmManagedAssembliesR2RRemap)" />
+      <_WasmManagedAssemblies Include="@(_WasmManagedAssembliesR2RRemap->'$(IntermediateLinkDir)%(FileName)%(Extension)')" />
+    </ItemGroup>
+
     <!-- Locate System.Private.CoreLib in runtime pack if not already bundled -->
     <PropertyGroup>
       <_HasCoreLib Condition="'%(_WasmManagedAssemblies.FileName)%(_WasmManagedAssemblies.Extension)' == 'System.Private.CoreLib.dll'">true</_HasCoreLib>
diff --git a/src/mono/browser/build/WasmApp.InTree.props b/src/mono/browser/build/WasmApp.InTree.props
index 2eb17ec0c0f94c..09f0d33488a0ce 100644
--- a/src/mono/browser/build/WasmApp.InTree.props
+++ b/src/mono/browser/build/WasmApp.InTree.props
@@ -24,6 +24,15 @@
     <UseMonoRuntime>true</UseMonoRuntime>
   </PropertyGroup>
 
+  <!-- In-tree R2R uses the in-build crossgen2. These two hooks must be props-time (property defaults live
+       in the CoreCLR .targets); both are inert unless PublishReadyToRun. See PR.md. -->
+  <PropertyGroup Condition="'$(RuntimeFlavor)' == 'CoreCLR' and '$(TargetOS)' == 'browser'">
+    <AfterMicrosoftNETSdkTargets Condition="'$(Crossgen2SdkOverrideTargetsPath)' != '' and Exists('$(Crossgen2SdkOverrideTargetsPath)')">$(AfterMicrosoftNETSdkTargets);$(Crossgen2SdkOverrideTargetsPath)</AfterMicrosoftNETSdkTargets>
+    <AfterMicrosoftNETSdkTargets>$(AfterMicrosoftNETSdkTargets);$(MSBuildThisFileDirectory)WasmApp.ReadyToRun.targets</AfterMicrosoftNETSdkTargets>
+  </PropertyGroup>
+  <Import Project="$(Crossgen2SdkOverridePropsPath)"
+          Condition="'$(RuntimeFlavor)' == 'CoreCLR' and '$(TargetOS)' == 'browser' and '$(Crossgen2SdkOverridePropsPath)' != '' and Exists('$(Crossgen2SdkOverridePropsPath)')" />
+
   <PropertyGroup Condition="'$(IsTestProject)' == 'true' or '$(IsOutputTypeLibrary)' == 'true'">
     <OutputType>library</OutputType>
   </PropertyGroup>
diff --git a/src/mono/browser/build/WasmApp.ReadyToRun.targets b/src/mono/browser/build/WasmApp.ReadyToRun.targets
new file mode 100644
index 00000000000000..1194acbb46f69d
--- /dev/null
+++ b/src/mono/browser/build/WasmApp.ReadyToRun.targets
@@ -0,0 +1,18 @@
+<Project>
+  <!-- In-tree only: override ResolveReadyToRunCompilers to use the in-build crossgen2 (mirrors
+       AppleBuild.ReadyToRun.targets). Imported after the SDK targets so it wins. -->
+  <Target Name="ResolveReadyToRunCompilers"
+          Condition="'$(PublishReadyToRun)' == 'true'"
+          DependsOnTargets="$(ResolveReadyToRunCompilersDependsOn)">
+    <PropertyGroup>
+      <Crossgen2Path>$([MSBuild]::NormalizePath('$(Crossgen2InBuildDir)', 'crossgen2$(ExeSuffix)'))</Crossgen2Path>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <Crossgen2Tool Include="$(Crossgen2Path)"
+                     TargetArch="$(TargetArchitecture)"
+                     TargetOS="$(TargetOS)"
+                     PerfmapFormatVersion="$(PublishReadyToRunPerfmapFormatVersion)"/>
+    </ItemGroup>
+  </Target>
+</Project>
diff --git a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets
new file mode 100644
index 00000000000000..fd6d1ffa9e0bbb
--- /dev/null
+++ b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets
@@ -0,0 +1,95 @@
+<!--
+***********************************************************************************************
+Microsoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets
+
+ReadyToRun for CoreCLR browser-wasm. See PR.md / dotnet/runtime#121257 for the full design.
+MUST be a .targets (not .props) and import on '== false' (not '!= true'): the SDK defaults
+UseMonoRuntime=true and imports .props before the body sets it false, and Mono apps leave it unset.
+
+Copyright (c) .NET Foundation. All rights reserved.
+***********************************************************************************************
+-->
+<Project>
+
+  <!-- Default R2R on for CoreCLR browser (mirrors AppleBuild.props); targets-time is early enough (consumed by later targets). -->
+  <PropertyGroup>
+    <PublishReadyToRun Condition="'$(PublishReadyToRun)' == ''">true</PublishReadyToRun>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(PublishReadyToRun)' == 'true'">
+    <!-- Force over SDK defaults: net11+ defaults ContainerFormat=pe (unloadable on wasm); staging requires non-composite. -->
+    <PublishReadyToRunContainerFormat Condition="'$(PublishReadyToRunContainerFormat)' != 'wasm'">wasm</PublishReadyToRunContainerFormat>
+    <PublishReadyToRunComposite Condition="'$(PublishReadyToRunComposite)' != 'false'">false</PublishReadyToRunComposite>
+    <!-- NYI/SIMD methods crossgen2 can't emit into R2R fall back to the runtime JIT. -->
+    <PublishReadyToRunCrossgen2ExtraArgs>$(PublishReadyToRunCrossgen2ExtraArgs);--codegenopt:JitWasmNyiToR2RUnsupported=1;--codegenopt:JitWasmSimdNyiToR2RUnsupported=1</PublishReadyToRunCrossgen2ExtraArgs>
+  </PropertyGroup>
+
+  <!-- Probe dirs for ConvertDllsToWebcil, separate for build vs publish (see PR.md):
+       build always uses the untrimmed pack images (a build is never trimmed; PublishTrimmed in the csproj
+       only configures publish); trimmed publish must use per-app crossgen output. _WasmPackR2RDir is set
+       here (target time) because _RuntimePackNativeDir is only set by _ResolveGlobalizationConfiguration. -->
+  <Target Name="_WasmCoreClrSelectR2RDirectories"
+          DependsOnTargets="_ResolveWasmConfiguration">
+    <PropertyGroup>
+      <_WasmPackR2RDir Condition="'$(_WasmPackR2RDir)' == '' and '$(_RuntimePackNativeDir)' != ''">$([MSBuild]::NormalizeDirectory('$(_RuntimePackNativeDir)', 'r2r'))</_WasmPackR2RDir>
+    </PropertyGroup>
+    <PropertyGroup Condition="'$(PublishReadyToRun)' == 'true'">
+      <_WasmPublishR2RDir Condition="'$(_WasmPublishR2RDir)' == ''">$([MSBuild]::NormalizeDirectory('$(IntermediateOutputPath)', 'R2R'))</_WasmPublishR2RDir>
+      <_WasmBuildPrebuiltR2RDirectories>$(_WasmPackR2RDir)</_WasmBuildPrebuiltR2RDirectories>
+      <_WasmPublishPrebuiltR2RDirectories Condition="'$(PublishTrimmed)' == 'true'">$(_WasmPublishR2RDir)</_WasmPublishPrebuiltR2RDirectories>
+      <_WasmPublishPrebuiltR2RDirectories Condition="'$(PublishTrimmed)' != 'true'">$(_WasmPackR2RDir)</_WasmPublishPrebuiltR2RDirectories>
+    </PropertyGroup>
+  </Target>
+
+  <!-- Prune raw pack R2R images (native/r2r/*.wasm) from build copy-local so the 90 MB closure never lands
+       loose in bin/; the managed .dll stays and ConvertDllsToWebcil stages the image. Unconditional (staging gated separately). -->
+  <Target Name="_WasmCoreClrPrunePackR2RFromBuild"
+          Condition="'$(_WasmEnableWebcil)' == 'true'"
+          DependsOnTargets="_WasmCoreClrSelectR2RDirectories"
+          BeforeTargets="_ComputeWasmBuildCandidates">
+    <ItemGroup>
+      <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
+        Condition="'%(Extension)' == '.wasm' and '$(_WasmPackR2RDir)' != '' and Exists('$(_WasmPackR2RDir)%(FileName).wasm')" />
+    </ItemGroup>
+  </Target>
+
+  <!-- Same prune for publish, before ProcessPublishFilesForWasm derives _WasmResolvedFilesToPublish. -->
+  <Target Name="_WasmCoreClrPruneR2RFromPublish"
+          Condition="'$(_WasmEnableWebcil)' == 'true'"
+          DependsOnTargets="_WasmCoreClrSelectR2RDirectories"
+          BeforeTargets="ProcessPublishFilesForWasm">
+    <ItemGroup>
+      <ResolvedFileToPublish Remove="@(ResolvedFileToPublish)"
+        Condition="'%(Extension)' == '.wasm' and '$(_WasmPackR2RDir)' != '' and Exists('$(_WasmPackR2RDir)%(FileName).wasm')" />
+    </ItemGroup>
+  </Target>
+
+  <!-- Feed the trimmed IL closure into mainline R2R as the compile+reference set (see PR.md "SWA vs iOS").
+       On the Blazor/SWA route ILLink stamps PostprocessAssembly=true on its own collection, not on
+       ResolvedFileToPublish, so the mainline compile list is empty and crossgen2 never runs. -->
+  <Target Name="_WasmFeedReadyToRunCompileList"
+          Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishTrimmed)' == 'true' and '$(PublishReadyToRunComposite)' != 'true' and '$(IntermediateLinkDir)' != ''"
+          BeforeTargets="_PrepareForReadyToRunCompilation">
+    <ItemGroup>
+      <!-- Clear the stale base-SDK R2R mark on the untrimmed runtime-pack copy (e.g. CoreLib under native/)
+           so crossgen resolves against the trimmed IL supplied below; it stays for webcil output. -->
+      <ResolvedFileToPublish Update="@(ResolvedFileToPublish)" PostprocessAssembly="false"
+        Condition="'%(ResolvedFileToPublish.PostprocessAssembly)' == 'true' and Exists('$(IntermediateLinkDir)%(ResolvedFileToPublish.FileName).dll')" />
+    </ItemGroup>
+    <ItemGroup>
+      <_WasmReadyToRunCompileInput Include="$(IntermediateLinkDir)*.dll" />
+      <ResolvedFileToPublish Include="@(_WasmReadyToRunCompileInput)"
+                             PostprocessAssembly="true"
+                             RelativePath="%(FileName)%(Extension)"
+                             CopyToPublishDirectory="PreserveNewest" />
+    </ItemGroup>
+  </Target>
+
+  <!-- Force crossgen (CreateReadyToRunImages) before ProcessPublishFilesForWasm: the latter runs
+       AfterTargets=ILLink, which a Blazor publish schedules ahead of R2R, so the images would ship too late. -->
+  <Target Name="_WasmEnsureReadyToRunBeforePublish"
+          Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' != 'true' and '$(WasmBuildingForNestedPublish)' != 'true'"
+          DependsOnTargets="CreateReadyToRunImages"
+          BeforeTargets="ProcessPublishFilesForWasm" />
+
+</Project>
diff --git a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
index 4ec8ade0ed5c92..b2ce682bb412bd 100644
--- a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
+++ b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
@@ -421,7 +421,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     Inputs="@(_WasmDllBuildCandidates);$(MSBuildProjectFullPath);$(MSBuildThisFileFullPath);$(_WebAssemblySdkTasksAssembly)"
     Outputs="@(_WasmDllBuildCandidates->'%(WebcilOutputPath)')">
 
-    <ConvertDllsToWebcil Candidates="@(_WasmDllBuildCandidates)" IntermediateOutputPath="$(_WasmBuildTmpWebcilPath)" OutputPath="$(_WasmBuildWebcilPath)" IsEnabled="$(_WasmEnableWebcil)" WebcilVersion="$(_WasmWebcilVersion)">
+    <ConvertDllsToWebcil Candidates="@(_WasmDllBuildCandidates)" IntermediateOutputPath="$(_WasmBuildTmpWebcilPath)" OutputPath="$(_WasmBuildWebcilPath)" IsEnabled="$(_WasmEnableWebcil)" WebcilVersion="$(_WasmWebcilVersion)" PrebuiltR2RDirectories="$(_WasmBuildPrebuiltR2RDirectories)">
       <Output TaskParameter="FileWrites" ItemName="FileWrites" />
       <Output TaskParameter="FileWrites" ItemName="_WasmConvertedWebcilOutputs" />
     </ConvertDllsToWebcil>
@@ -1010,7 +1010,7 @@ Copyright (c) .NET Foundation. All rights reserved.
       <_WasmPublishTmpWebcilPath>$([MSBuild]::NormalizeDirectory($(IntermediateOutputPath), 'tmp-webcil', 'publish'))</_WasmPublishTmpWebcilPath>
     </PropertyGroup>
 
-    <ConvertDllsToWebcil Candidates="@(_NewWasmPublishStaticWebAssets)" IntermediateOutputPath="$(_WasmPublishTmpWebcilPath)" OutputPath="$(_WasmPublishWebcilPath)" IsEnabled="$(_WasmEnableWebcil)" WebcilVersion="$(_WasmWebcilVersion)">
+    <ConvertDllsToWebcil Candidates="@(_NewWasmPublishStaticWebAssets)" IntermediateOutputPath="$(_WasmPublishTmpWebcilPath)" OutputPath="$(_WasmPublishWebcilPath)" IsEnabled="$(_WasmEnableWebcil)" WebcilVersion="$(_WasmWebcilVersion)" PrebuiltR2RDirectories="$(_WasmPublishPrebuiltR2RDirectories)">
       <Output TaskParameter="WebcilCandidates" ItemName="_NewWebcilPublishStaticWebAssetsCandidates" />
       <Output TaskParameter="FileWrites" ItemName="FileWrites" />
     </ConvertDllsToWebcil>
@@ -1358,4 +1358,8 @@ Copyright (c) .NET Foundation. All rights reserved.
       <TrimmerRootAssembly Include="$(AssemblyName)" RootMode="all" />
     </ItemGroup>
   </Target>
+
+  <!-- CoreCLR browser-wasm R2R, isolated from Mono. '== false' (not '!= true'): Mono apps leave UseMonoRuntime unset. -->
+  <Import Project="$(MSBuildThisFileDirectory)Microsoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets"
+          Condition="'$(UseMonoRuntime)' == 'false'" />
 </Project>
diff --git a/src/mono/sample/wasm/browser-advanced/Wasm.Advanced.Sample.csproj b/src/mono/sample/wasm/browser-advanced/Wasm.Advanced.Sample.csproj
index 365a61629523a8..4e60eba8c42df9 100644
--- a/src/mono/sample/wasm/browser-advanced/Wasm.Advanced.Sample.csproj
+++ b/src/mono/sample/wasm/browser-advanced/Wasm.Advanced.Sample.csproj
@@ -21,6 +21,7 @@
     <_ExtraTrimmerArgs>$(_ExtraTrimmerArgs) --dump-dependencies</_ExtraTrimmerArgs>
 
     <!-- 
+    <PublishReadyToRun>true</PublishReadyToRun>
     <RunAOTCompilation>true</RunAOTCompilation>
     <WasmNativeDebugSymbols>true</WasmNativeDebugSymbols>
     <WasmNativeStrip>false</WasmNativeStrip>
diff --git a/src/mono/sample/wasm/console-node/Wasm.Console.Node.Sample.csproj b/src/mono/sample/wasm/console-node/Wasm.Console.Node.Sample.csproj
index 5e9ae0d965fe6f..119c1183a53c0c 100644
--- a/src/mono/sample/wasm/console-node/Wasm.Console.Node.Sample.csproj
+++ b/src/mono/sample/wasm/console-node/Wasm.Console.Node.Sample.csproj
@@ -7,6 +7,7 @@
     <GenerateRunScriptForSample Condition="'$(ArchiveTests)' == 'true'">true</GenerateRunScriptForSample>
     <ExpectedExitCode>2</ExpectedExitCode>
     <RunScriptCommand>$(ExecXHarnessVar) wasm test --app=. --engine=NodeJS --engine-arg=--stack-trace-limit=1000 --js-file=main.mjs --output-directory=$(XHarnessOutputVar) --expected-exit-code $(ExpectedExitCode)</RunScriptCommand>
+    <PublishReadyToRun>true</PublishReadyToRun>
   </PropertyGroup>
 
   <Target Name="RunSample" DependsOnTargets="RunSampleWithNode" />
diff --git a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/ConvertDllsToWebCil.cs b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/ConvertDllsToWebCil.cs
index 5e629238b8fec8..f2d90385c636f8 100644
--- a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/ConvertDllsToWebCil.cs
+++ b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/ConvertDllsToWebCil.cs
@@ -23,6 +23,13 @@ public class ConvertDllsToWebcil : Task
     [Required]
     public bool IsEnabled { get; set; }
 
+    /// <summary>
+    /// Directories holding prebuilt R2R webcil-in-wasm images (CoreCLR browser). For a managed non-culture
+    /// .dll candidate with empty <c>R2RWebcilPath</c>, the first matching image is staged instead of
+    /// converting the IL. Empty for Mono.
+    /// </summary>
+    public string[] PrebuiltR2RDirectories { get; set; }
+
     public int WebcilVersion { get; set; }
 
     [Output]
@@ -137,6 +144,31 @@ private TaskItem ConvertDll(string tmpDir, ITaskItem candidate)
         // stage (copy) it into the webcil output so it flows through the same downstream metadata as a
         // converted assembly, but carries native code. The .dll is kept only as the metadata source.
         string r2rWebcilPath = candidate.GetMetadata("R2RWebcilPath");
+        if (string.IsNullOrEmpty(r2rWebcilPath) && !isCulture && PrebuiltR2RDirectories != null)
+        {
+            string assemblyName = Path.GetFileNameWithoutExtension(dllFilePath);
+            foreach (string dir in PrebuiltR2RDirectories)
+            {
+                if (string.IsNullOrEmpty(dir))
+                    continue;
+
+                // Probe .dll before .wasm: per-app crossgen (--out:<name>.dll) writes the R2R image to
+                // <name>.dll and can leave a same-named <name>.wasm that is NOT it. Pack images are
+                // <name>.wasm with no sibling .dll, so they still resolve.
+                string candidateWasm = Path.Combine(dir, assemblyName + Utils.WebcilInWasmExtension);
+                string candidateDll = Path.Combine(dir, assemblyName + ".dll");
+                if (File.Exists(candidateDll))
+                {
+                    r2rWebcilPath = candidateDll;
+                    break;
+                }
+                if (File.Exists(candidateWasm))
+                {
+                    r2rWebcilPath = candidateWasm;
+                    break;
+                }
+            }
+        }
         if (!string.IsNullOrEmpty(r2rWebcilPath))
         {
             if (Utils.IsNewerThan(r2rWebcilPath, finalWebcil))