From b581af1968d4b75ad74696019aa865f2de78f3a8 Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Thu, 24 Sep 2026 16:06:11 -0500
Subject: [PATCH 01/11] [wasm][coreclr] Enable composite ReadyToRun publishing

Enable composite R2R output for browser CoreCLR, load the owner image before runtime initialization, and preserve component stubs and linked inputs across incremental publishes. Fix WebCIL function relocations and add browser publish coverage.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../testing/libraries/testing-wasm.md         |   8 ++
 .../ObjectWriter/WebCilObjectWriter.cs        |   7 ++
 ...ET.Sdk.WebAssembly.Browser.CoreCLR.targets |  52 +++++----
 ...rosoft.NET.Sdk.WebAssembly.Browser.targets |  42 +++++++-
 .../wasm/Wasm.Build.Tests/ReadyToRunTests.cs  | 100 ++++++++++++++++--
 .../libs/Common/JavaScript/host/host.ts       |   4 +-
 .../libs/Common/JavaScript/loader/assets.ts   |  17 ++-
 .../libs/Common/JavaScript/loader/run.ts      |   4 +-
 .../GenerateWasmBootJson.cs                   |   7 ++
 9 files changed, 205 insertions(+), 36 deletions(-)

diff --git a/docs/workflow/testing/libraries/testing-wasm.md b/docs/workflow/testing/libraries/testing-wasm.md
index 4906192c6c1600..2dfb6d67e12cbb 100644
--- a/docs/workflow/testing/libraries/testing-wasm.md
+++ b/docs/workflow/testing/libraries/testing-wasm.md
@@ -194,6 +194,14 @@ stale staged assets can otherwise cause assembly-loading failures before tests s
 The `LibraryTestsCoreCLR_R2R` CI jobs use the same configuration and archive the published
 tests for execution on Helix. The existing interpreter jobs remain separate.
 
+For CoreCLR browser applications, set `PublishReadyToRun=true` and
+`PublishReadyToRunComposite=true` to publish a single composite ReadyToRun image and
+component WebCIL stubs instead of per-assembly images. Publishing requires a wasm-capable
+crossgen2 and WebCIL enabled; the composite is loaded before the runtime starts.
+`ReadyToRunTests.PublishRunAllPagesComposite` exercises trimmed, untrimmed, and
+native-relinked publishes in a browser, including asset fingerprinting when
+`USE_FINGERPRINTING_FOR_TESTS=true`.
+
 ## AOT library tests
 
 - Building library tests with AOT, and (even) with `EnableAggressiveTrimming` takes 3-9mins on CI, and that adds up for all the assemblies, causing
diff --git a/src/coreclr/tools/Common/Compiler/ObjectWriter/WebCilObjectWriter.cs b/src/coreclr/tools/Common/Compiler/ObjectWriter/WebCilObjectWriter.cs
index d61c5757135988..d9f74730988802 100644
--- a/src/coreclr/tools/Common/Compiler/ObjectWriter/WebCilObjectWriter.cs
+++ b/src/coreclr/tools/Common/Compiler/ObjectWriter/WebCilObjectWriter.cs
@@ -853,6 +853,9 @@ private unsafe int ResolveReloc(int sectionIndex, MemoryStream sourceStream, lon
                     case RelocType.WASM_TABLE_INDEX_SLEB:
                     case RelocType.WASM_TABLE_INDEX_REL_I32:
                     case RelocType.WASM_FUNCTION_INDEX_LEB:
+                    // A code-section address names a function index, not an offset into the WebCIL payload.
+                    case RelocType.WASM_MEMORY_ADDR_REL_SLEB when
+                        _sections[definedSymbol.SectionIndex] is WasmSection { Type: WasmSectionType.Code }:
                     {
                         // These relocations reference a wasm structural index (function, type,
                         // table entry, or well-known global). For R2R we self-resolve them here to
@@ -861,6 +864,10 @@ private unsafe int ResolveReloc(int sectionIndex, MemoryStream sourceStream, lon
                         {
                             throw new InvalidOperationException($"Symbol '{reloc.SymbolName}' was not registered. Relocation type {reloc.Type}.");
                         }
+                        if (reloc.Type == RelocType.WASM_MEMORY_ADDR_REL_SLEB && symbol.IndexSpace != WasmIndexSpace.Function)
+                        {
+                            throw new InvalidDataException($"Code-section relocation for '{reloc.SymbolName}' does not reference a function.");
+                        }
 
                         if (shrink && Relocation.IsVariableLength(reloc.Type))
                         {
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
index cb7de8a0102550..159fa921ddd56b 100644
--- 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
@@ -21,7 +21,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     <!-- Override only the incompatible SDK default: net11+ defaults ContainerFormat=pe (unloadable on wasm).
          An explicit unsupported value is left as-is and rejected by _WasmCoreClrSelectR2RDirectories. -->
     <PublishReadyToRunContainerFormat Condition="'$(PublishReadyToRunContainerFormat)' == '' or '$(PublishReadyToRunContainerFormat)' == 'pe'">wasm</PublishReadyToRunContainerFormat>
-    <!-- Default non-composite when unset; an explicit composite request is rejected below. -->
+    <!-- Keep the existing per-assembly behavior unless composite is explicitly requested. -->
     <PublishReadyToRunComposite Condition="'$(PublishReadyToRunComposite)' == ''">false</PublishReadyToRunComposite>
     <!-- Compile every assembly into one shared (large) version bubble. -->
     <PublishReadyToRunCrossgen2ExtraArgs>$(PublishReadyToRunCrossgen2ExtraArgs);--opt-cross-module:*</PublishReadyToRunCrossgen2ExtraArgs>
@@ -51,14 +51,14 @@ Copyright (c) .NET Foundation. All rights reserved.
     </PropertyGroup>
   </Target>
 
-  <!-- Fail comprehensibly instead of emitting composite/PE images the runtime cannot load. The config checks
+  <!-- Fail comprehensibly instead of emitting PE images the runtime cannot load. The config checks
        run on both build and publish; the crossgen2 requirement is publish-only, since a dev-loop build stages
        the pack R2R and never invokes crossgen2. -->
   <Target Name="_WasmCoreClrValidateReadyToRun"
           Condition="'$(PublishReadyToRun)' == 'true'"
-          BeforeTargets="_WasmCoreClrSelectR2RDirectories">
-    <Error Condition="'$(PublishReadyToRunComposite)' == 'true'"
-           Text="PublishReadyToRunComposite is not supported for CoreCLR browser-wasm; only non-composite (per-assembly) R2R images are supported." />
+          BeforeTargets="_WasmCoreClrSelectR2RDirectories;_ResolveWasmOutputs">
+    <Error Condition="'$(PublishReadyToRunComposite)' == 'true' and '$(_WasmEnableWebcil)' != 'true'"
+           Text="PublishReadyToRunComposite for CoreCLR browser-wasm requires WebCIL-in-Wasm assemblies; enable WasmEnableWebcil." />
     <Error Condition="'$(PublishReadyToRunContainerFormat)' != 'wasm'"
            Text="PublishReadyToRunContainerFormat '$(PublishReadyToRunContainerFormat)' is not supported for CoreCLR browser-wasm; only 'wasm' is supported." />
     <Error Condition="('$(_IsPublishing)' == 'true' or '$(WasmBuildingForNestedPublish)' == 'true' or '$(WasmBuildOnlyAfterPublish)' == 'true') and ('$(Crossgen2InBuildDir)' == '' or !Exists('$(Crossgen2InBuildDir)')) and '@(ResolvedCrossgen2Pack)' == ''"
@@ -69,6 +69,7 @@ Copyright (c) .NET Foundation. All rights reserved.
        PublishReadyToRun selects its flavour, so it belongs in the webcil staging stamp too. -->
   <ItemGroup>
     <_WasmWebcilStampProperty Include="PublishTrimmed" />
+    <_WasmWebcilStampProperty Include="PublishReadyToRunComposite" />
   </ItemGroup>
 
   <!-- Prune raw pack R2R images (native/r2r/*.wasm) from build copy-local so the 90 MB closure never lands
@@ -150,14 +151,26 @@ Copyright (c) .NET Foundation. All rights reserved.
        publish, and _GatherWasmFilesToPublish when a native relink is in play. The relink crossgens inside
        WasmNestedPublishApp, where ProcessPublishFilesForWasm is never scheduled; without the second hook every
        crossgen'd assembly is still named .wasm when _GatherWasmFilesToPublish filters to .dll and silently drops
-       out of the bundle - a publish that exits 0 with no System.Private.CoreLib. -->
+       out of the bundle - a publish that exits 0 with no System.Private.CoreLib. In composite mode, restore
+       all component IL candidates so ConvertDllsToWebcil can stage their forwarding stubs; the composite
+       itself is separately defined as a publish static web asset. -->
   <Target Name="_WasmCoreClrRoutePerAppR2RToFramework"
           Condition="'$(_WasmEnableWebcil)' == 'true' and '$(PublishReadyToRun)' == 'true'"
           DependsOnTargets="_WasmCoreClrSelectR2RDirectories;CreateReadyToRunImages"
           BeforeTargets="ProcessPublishFilesForWasm;_GatherWasmFilesToPublish">
     <ItemGroup>
-      <ResolvedFileToPublish Remove="@(_ReadyToRunCompileList->'%(OutputR2RImage)')" />
+      <ResolvedFileToPublish Remove="@(_ReadyToRunCompileList->'%(OutputR2RImage)')"
+                             Condition="'$(PublishReadyToRunComposite)' != 'true'" />
       <ResolvedFileToPublish Include="@(_ReadyToRunCompileList)"
+                             RelativePath="%(FileName)%(Extension)"
+                             CopyToPublishDirectory="PreserveNewest"
+                             Condition="'$(PublishReadyToRunComposite)' != 'true'" />
+      <_WasmCompositeR2RInput Include="@(_ReadyToRunCompositeBuildInput);@(_ReadyToRunCompositeUnrootedBuildInput);@(_ReadyToRunCompileList->WithMetadataValue('CreateCompositeImage', ''))"
+                              Condition="'$(PublishReadyToRunComposite)' == 'true'" />
+      <_WasmCompositeR2RImage Include="@(_ReadyToRunFilesToPublish)"
+                              Condition="'$(PublishReadyToRunComposite)' == 'true' and '%(Extension)' == '.wasm'" />
+      <ResolvedFileToPublish Remove="@(_WasmCompositeR2RInput);@(_WasmCompositeR2RImage)" />
+      <ResolvedFileToPublish Include="@(_WasmCompositeR2RInput)"
                              RelativePath="%(FileName)%(Extension)"
                              CopyToPublishDirectory="PreserveNewest" />
     </ItemGroup>
@@ -167,7 +180,7 @@ Copyright (c) .NET Foundation. All rights reserved.
        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)' != ''"
+          Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishTrimmed)' == 'true' and '$(IntermediateLinkDir)' != ''"
           BeforeTargets="_PrepareForReadyToRunCompilation">
     <ItemGroup>
       <!-- Clear the stale base-SDK R2R mark on the untrimmed runtime-pack copy (e.g. CoreLib under native/)
@@ -192,38 +205,35 @@ Copyright (c) .NET Foundation. All rights reserved.
   <!-- Force crossgen (CreateReadyToRunImages) before ProcessPublishFilesForWasm: the latter runs
        AfterTargets=ILLink, which a Blazor publish schedules ahead of R2R, so the images would ship too late. -->
   <Target Name="_WasmEnsureReadyToRunBeforePublish"
-          Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' != 'true' and '$(WasmBuildingForNestedPublish)' != 'true'"
+          Condition="'$(PublishReadyToRun)' == 'true' and '$(WasmBuildingForNestedPublish)' != 'true'"
           DependsOnTargets="CreateReadyToRunImages"
           BeforeTargets="ProcessPublishFilesForWasm" />
 
-  <!-- Per-app crossgen must be conservative: any change has to recompile EVERY per-app R2R image, because
-       cross-module inlining lets any image inline from any other and a stale image fail-fasts at startup.
-       _CreateR2RImages batches its Outputs per assembly, which alone would rebuild only the changed image;
-       adding the whole closure and the compiler as non-correlated inputs makes the whole target re-run.
-       Mirrors the framework build's sfxproj _ReadyToRunCompilerInputs. -->
+  <!-- Per-app crossgen must be conservative: cross-module inlining makes all images depend on the
+       whole closure. Include reference-only assemblies and the compiler as non-correlated inputs
+       so _CreateR2RImages reruns even when its per-assembly outputs are otherwise up-to-date. -->
   <Target Name="_WasmCoreClrConservativeR2RInputs"
-          Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' != 'true'"
+          Condition="'$(PublishReadyToRun)' == 'true'"
           BeforeTargets="_CreateR2RImages">
     <ItemGroup>
-      <_ReadyToRunCompilerInputs Include="@(_ReadyToRunCompileList);@(_ReadyToRunAssembliesToReference)" />
+      <_ReadyToRunCompilerInputs Include="@(_ReadyToRunCompileList);@(_ReadyToRunAssembliesToReference);@(_ReadyToRunCompositeBuildReferences);@(_ReadyToRunCompositeUnrootedBuildInput)" />
       <!-- crossgen2 itself, not just the JIT: an updated compiler with an unchanged JIT must still invalidate. -->
       <_ReadyToRunCompilerInputs Include="$(_WasmResolvedCrossgen2Dir)crossgen2*;$(_WasmResolvedCrossgen2Dir)clrjit_universal_wasm_*"
                                  Condition="'$(_WasmResolvedCrossgen2Dir)' != ''" />
     </ItemGroup>
   </Target>
 
-  <!-- Delete per-app R2R images left in obj/R2R by a previous build whose assembly is no longer in the compile
-       closure. A stale orphan would otherwise be staged and fail-fast at load. Mirrors the framework build's
-       sfxproj _WasmFrameworkR2RLayoutObsolete. -->
+  <!-- Delete per-app images and composite component stubs left in obj/R2R by a previous build or
+       publish mode. A stale orphan would otherwise be staged and fail-fast at load. -->
   <Target Name="_WasmCoreClrPruneStalePerAppR2R"
-          Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' != 'true'"
+          Condition="'$(PublishReadyToRun)' == 'true'"
           DependsOnTargets="_WasmCoreClrSelectR2RDirectories"
           AfterTargets="_CreateR2RImages">
     <ItemGroup Condition="'$(_WasmPublishR2RDir)' != '' and Exists('$(_WasmPublishR2RDir)')">
       <!-- Both extensions: ConvertDll probes PrebuiltR2RDirectory for .dll before .wasm (a stock SDK names the
            R2R output <name>.dll), so a surviving .dll would win the probe over the current .wasm. -->
       <_WasmStalePerAppR2R Include="$(_WasmPublishR2RDir)*.wasm;$(_WasmPublishR2RDir)*.dll"
-                           Exclude="@(_ReadyToRunCompileList->'%(OutputR2RImage)')" />
+                           Exclude="@(_ReadyToRunFilesToPublish)" />
     </ItemGroup>
     <Delete Files="@(_WasmStalePerAppR2R)" />
   </Target>
diff --git a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
index 529106d2dc6a94..2710416f5efa3d 100644
--- a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
+++ b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
@@ -1024,6 +1024,18 @@ Copyright (c) .NET Foundation. All rights reserved.
       <_WasmResolvedFilesToPublish Include="@(ResolvedFileToPublish)"
         Condition="'%(ResolvedFileToPublish.CopyToPublishDirectory)' != 'Never'" />
     </ItemGroup>
+    <!-- When WasmAssembliesFinal contains only the project assembly on an incremental trimmed
+         publish, WasmAssembliesToBundle removes the linked closure from ResolvedFileToPublish.
+         Keep the R2R inputs as publish candidates so their staged images stay in boot. -->
+    <ItemGroup Condition="'$(UseMonoRuntime)' == 'false' and '$(PublishReadyToRun)' == 'true' and @(WasmAssembliesFinal->Count()) > 0">
+      <_WasmResolvedFilesToPublish Include="@(_WasmCompositeR2RInput)"
+                                   Condition="'$(PublishReadyToRunComposite)' == 'true'" />
+      <_WasmResolvedFilesToPublish Include="@(_WasmReadyToRunCompileInput)"
+                                   RelativePath="%(FileName)%(Extension)"
+                                   Condition="'$(PublishReadyToRunComposite)' != 'true' and '$(PublishTrimmed)' == 'true'" />
+      <_WasmResolvedFilesToPublish Include="@(_ReadyToRunCompileList)"
+                                   Condition="'$(PublishReadyToRunComposite)' != 'true' and '$(PublishTrimmed)' != 'true'" />
+    </ItemGroup>
 
     <ComputeWasmPublishAssets
       ResolvedFilesToPublish="@(_WasmResolvedFilesToPublish)"
@@ -1046,7 +1058,30 @@ Copyright (c) .NET Foundation. All rights reserved.
       <Output TaskParameter="PromotedAssets" ItemName="_PromotedWasmPublishStaticWebAssets" />
       <Output TaskParameter="FilesToRemove" ItemName="_PublishResolvedFilesToRemove" />
     </ComputeWasmPublishAssets>
-    
+
+    <ItemGroup Condition="'$(UseMonoRuntime)' == 'false' and '$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' == 'true'">
+      <_WasmCompositeCompilation Include="@(_ReadyToRunCompileList)"
+                                 Condition="'%(CreateCompositeImage)' == 'true'" />
+      <_WasmCompositePublishCandidate Include="@(_WasmCompositeCompilation->'%(OutputR2RImage)')">
+        <SourceId>$(PackageId)</SourceId>
+        <SourceType>Computed</SourceType>
+        <ContentRoot>$([MSBuild]::NormalizeDirectory($(PublishDir), 'wwwroot'))</ContentRoot>
+        <BasePath>$(StaticWebAssetBasePath)</BasePath>
+        <RelativePath Condition="'$(_WasmFingerprintAssets)' != 'true'">_framework/$([System.IO.Path]::GetFileName('%(OutputR2RImage)'))</RelativePath>
+        <RelativePath Condition="'$(_WasmFingerprintAssets)' == 'true'">_framework/$([System.IO.Path]::GetFileNameWithoutExtension('%(OutputR2RImage)'))#[.{fingerprint}]!.wasm</RelativePath>
+        <AssetKind>Publish</AssetKind>
+        <AssetMode>All</AssetMode>
+        <AssetRole>Primary</AssetRole>
+        <AssetTraitName>WasmResource</AssetTraitName>
+        <AssetTraitValue>core</AssetTraitValue>
+        <CopyToOutputDirectory>Never</CopyToOutputDirectory>
+        <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
+        <OriginalItemSpec>%(OutputR2RImage)</OriginalItemSpec>
+      </_WasmCompositePublishCandidate>
+    </ItemGroup>
+    <Error Condition="'$(UseMonoRuntime)' == 'false' and '$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' == 'true' and '@(_WasmCompositePublishCandidate)' == ''"
+           Text="Composite ReadyToRun compilation did not produce a composite WebAssembly image." />
+
     <ItemGroup Condition="'$(_WasmInlineBootConfig)' == 'true'">
       <_WasmDotnetJsForPublish Include="@(ResolvedFileToPublish)" Condition="'%(FileName)%(Extension)' == 'dotnet.js'" />
     </ItemGroup>
@@ -1065,6 +1100,7 @@ Copyright (c) .NET Foundation. All rights reserved.
       <_WasmPublishWebcilStampLine Include="_WasmEnableWebcil=$(_WasmEnableWebcil)" />
       <_WasmPublishWebcilStampLine Include="_WasmWebcilVersion=$(_WasmWebcilVersion)" />
       <_WasmPublishWebcilStampLine Include="PublishReadyToRun=$(PublishReadyToRun)" />
+      <_WasmPublishWebcilStampLine Include="PublishReadyToRunComposite=$(PublishReadyToRunComposite)" />
       <_WasmPublishWebcilStampLine Include="_WasmPublishPrebuiltR2RDirectory=$(_WasmPublishPrebuiltR2RDirectory)" />
       <_WasmPublishWebcilStampLine Include="PrebuiltR2R=%(_WasmPublishPrebuiltR2RInput.Identity)|%(_WasmPublishPrebuiltR2RInput.ModifiedTime)" />
       <_WasmPublishWebcilStampLine Include="Input=%(_WasmPublishWebcilStampInput.Identity)|%(_WasmPublishWebcilStampInput.ModifiedTime)" />
@@ -1090,7 +1126,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     -->
     <ItemGroup>
       <_NewWebcilPublishStaticWebAssetsCandidatesNoMetadata
-        Include="@(_NewWebcilPublishStaticWebAssetsCandidates)"
+        Include="@(_NewWebcilPublishStaticWebAssetsCandidates);@(_WasmCompositePublishCandidate)"
         RemoveMetadata="Integrity;Fingerprint" />
       <!-- Set per-item ContentRoot so each asset's Identity matches its actual file on disk.
            Clear stale Fingerprint/Integrity so DefineStaticWebAssets recomputes from the actual file. -->
@@ -1273,7 +1309,7 @@ Copyright (c) .NET Foundation. All rights reserved.
   <Target Name="_WriteWasmPublishBootJsonPropertyStamp"
     DependsOnTargets="_ResolvePublishWasmBootJsonInputs">
     <PropertyGroup>
-      <_WasmBootJsonPublishStampContent>$(WasmDebugLevel)|$(_WasmPublishApplicationEnvironmentName)|$(_BlazorCacheBootResources)|$(InvariantGlobalization)|$(_LoadCustomIcuData)|$(_BlazorWebAssemblyLoadAllGlobalizationData)|$(_BlazorWebAssemblyJiterpreter)|$(_BlazorWebAssemblyRuntimeOptions)|$(RunAOTCompilation)|$(WasmEnableThreads)|$(UseMonoRuntime)|$(_WasmFingerprintAssets)|$(_WasmBundlerFriendlyBootConfig)|$(WasmProfilers)|$(TargetFrameworkVersion)|$(DiagnosticPorts)|$(StaticWebAssetStandaloneHosting)|@(WasmEnvironmentVariable->'%(Identity)=%(Value)')|@(BlazorWebAssemblyLazyLoad)|@(WasmModuleAfterConfigLoaded)|@(WasmModuleAfterRuntimeReady)|$(WasmTestExitOnUnhandledError)|$(WasmTestAppendElementOnExit)|$(WasmTestLogExitCode)|$(WasmTestAsyncFlushOnExit)</_WasmBootJsonPublishStampContent>
+      <_WasmBootJsonPublishStampContent>$(WasmDebugLevel)|$(_WasmPublishApplicationEnvironmentName)|$(_BlazorCacheBootResources)|$(InvariantGlobalization)|$(_LoadCustomIcuData)|$(_BlazorWebAssemblyLoadAllGlobalizationData)|$(_BlazorWebAssemblyJiterpreter)|$(_BlazorWebAssemblyRuntimeOptions)|$(RunAOTCompilation)|$(WasmEnableThreads)|$(UseMonoRuntime)|$(PublishReadyToRunComposite)|$(_WasmFingerprintAssets)|$(_WasmBundlerFriendlyBootConfig)|$(WasmProfilers)|$(TargetFrameworkVersion)|$(DiagnosticPorts)|$(StaticWebAssetStandaloneHosting)|@(WasmEnvironmentVariable->'%(Identity)=%(Value)')|@(BlazorWebAssemblyLazyLoad)|@(WasmModuleAfterConfigLoaded)|@(WasmModuleAfterRuntimeReady)|$(WasmTestExitOnUnhandledError)|$(WasmTestAppendElementOnExit)|$(WasmTestLogExitCode)|$(WasmTestAsyncFlushOnExit)</_WasmBootJsonPublishStampContent>
     </PropertyGroup>
     <WriteLinesToFile
       File="$(IntermediateOutputPath)wasm-bootjson-publish.stamp"
diff --git a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
index 4788ef6bfd32e3..7ab5a726df92d1 100644
--- a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
@@ -6,6 +6,7 @@
 using System.Linq;
 using System.Text.RegularExpressions;
 using System.Threading.Tasks;
+using Microsoft.NET.Sdk.WebAssembly;
 using Microsoft.NET.WebAssembly.Webcil;
 using Microsoft.Playwright;
 using Xunit;
@@ -53,7 +54,15 @@ await RunForBuildWithDotnetRun(new BlazorRunOptions(config,
         [InlineData(Configuration.Release, /*trimmed*/ false)]
         [TestCategory("no-workload")]
         public Task PublishRunAllPages(Configuration config, bool trimmed)
-            => PublishRunAllPagesCore(config, trimmed, nativeRelink: false);
+            => PublishRunAllPagesCore(config, trimmed, nativeRelink: false, composite: false);
+
+        [ConditionalTheory(typeof(BuildTestBase), nameof(IsCoreClrRuntime))]
+        [InlineData(Configuration.Release, /*trimmed*/ true, /*nativeRelink*/ false)]
+        [InlineData(Configuration.Release, /*trimmed*/ false, /*nativeRelink*/ false)]
+        [InlineData(Configuration.Release, /*trimmed*/ true, /*nativeRelink*/ true)]
+        [TestCategory("no-workload")]
+        public Task PublishRunAllPagesComposite(Configuration config, bool trimmed, bool nativeRelink)
+            => PublishRunAllPagesCore(config, trimmed, nativeRelink, composite: true);
 
         // CoreCLR relinks dotnet.native.wasm for Blazor when WasmBuildNative=true; the relink is driven by the
         // IsBrowserWasmProject triggers in BrowserWasmApp.CoreCLR.targets. AssertBundle(isNativeBuild: true)
@@ -63,15 +72,21 @@ public Task PublishRunAllPages(Configuration config, bool trimmed)
         [InlineData(Configuration.Release, /*trimmed*/ false)]
         [TestCategory("no-workload")]
         public Task PublishRunAllPagesNativeRelink(Configuration config, bool trimmed)
-            => PublishRunAllPagesCore(config, trimmed, nativeRelink: true);
+            => PublishRunAllPagesCore(config, trimmed, nativeRelink: true, composite: false);
 
-        private async Task PublishRunAllPagesCore(Configuration config, bool trimmed, bool nativeRelink)
+        private async Task PublishRunAllPagesCore(Configuration config, bool trimmed, bool nativeRelink, bool composite)
         {
             // Publish runs per-app crossgen2 for the whole closure, trimmed or not: even the untrimmed CoreLib
             // is a per-app image, not the runtime pack's. nativeRelink also relinks dotnet.native.wasm.
-            string label = $"r2r_pub_{(trimmed ? "trim" : "notrim")}{(nativeRelink ? "_native" : "")}";
+            string label = $"r2r_pub_{(trimmed ? "trim" : "notrim")}{(nativeRelink ? "_native" : "")}{(composite ? "_composite" : "")}";
+            string extraItems = composite
+                ? """<ProjectReference Include="../R2rSuffixLibrary/R2rSuffixLibrary.csproj" /><TrimmerRootAssembly Include="R2rSuffixLibrary.r2r" />"""
+                : string.Empty;
             ProjectInfo info = CopyTestAsset(config, aot: false, TestAsset.BlazorBasicTestApp, label,
-                extraProperties: $"<PublishReadyToRun>true</PublishReadyToRun><PublishTrimmed>{(trimmed ? "true" : "false")}</PublishTrimmed>");
+                extraProperties: $"<PublishReadyToRun>true</PublishReadyToRun><PublishReadyToRunComposite>{(composite ? "true" : "false")}</PublishReadyToRunComposite><PublishTrimmed>{(trimmed ? "true" : "false")}</PublishTrimmed>",
+                extraItems: extraItems);
+            if (composite)
+                AddR2RSuffixLibrary(info);
             string extraArgs = GetR2RBuildArgs(config);
             if (nativeRelink)
             {
@@ -86,12 +101,23 @@ private async Task PublishRunAllPagesCore(Configuration config, bool trimmed, bo
                 isNativeBuild: nativeRelink ? true : (bool?)null);
 
             string frameworkDir = GetBlazorBinFrameworkDir(config, forPublish: true);
-            AssertCoreLibReadyToRun(frameworkDir, expectReadyToRun: true);
+            if (composite)
+                AssertCompositeReadyToRun(frameworkDir);
+            else
+                AssertCoreLibReadyToRun(frameworkDir, expectReadyToRun: true);
             AssertNoDuplicateAssemblies(frameworkDir);
             AssertNoManagedAssembliesOutsideFramework(frameworkDir);
             AssertTrimmedClosureIsFullyStaged(config, frameworkDir);
             AssertPerAppCrossgenRan(config, expected: true);
 
+            if (trimmed && !nativeRelink)
+            {
+                BlazorPublish(info, config, new PublishOptions(UseCache: false, ExtraMSBuildArgs: extraArgs));
+                if (composite)
+                    AssertCompositeReadyToRun(frameworkDir);
+                AssertNoDuplicateAssemblies(frameworkDir);
+            }
+
             await RunForPublishWithWebServer(new BlazorRunOptions(config,
                 CheckCounter: false,
                 ExecuteAfterLoaded: (_, page) => InteractAllPagesAsync(page)));
@@ -110,6 +136,19 @@ public void FrameworkAssembliesAreNotReadyToRunWhenDisabled(Configuration config
             AssertPerAppCrossgenRan(config, expected: false);
         }
 
+        [ConditionalTheory(typeof(BuildTestBase), nameof(IsCoreClrRuntime))]
+        [InlineData(Configuration.Release)]
+        [TestCategory("no-workload")]
+        public void CompositeRequiresWebcil(Configuration config)
+        {
+            ProjectInfo info = CopyTestAsset(config, aot: false, TestAsset.BlazorBasicTestApp, "r2r_composite_no_webcil",
+                extraProperties: "<PublishReadyToRun>true</PublishReadyToRun><PublishReadyToRunComposite>true</PublishReadyToRunComposite><WasmEnableWebcil>false</WasmEnableWebcil>");
+            (string _, string output) = BlazorPublish(info, config,
+                new PublishOptions(ExpectSuccess: false, ExtraMSBuildArgs: GetR2RBuildArgs(config)));
+
+            Assert.Contains("PublishReadyToRunComposite for CoreCLR browser-wasm requires WebCIL-in-Wasm assemblies", output);
+        }
+
         // Navigate Home -> Counter (increment 0 -> 1) -> Weather (forecast rows) -> Home, asserting content
         // at each step. DetectRuntimeFailures (default) fails the run on any unhandled managed/JS exception.
         private static async Task InteractAllPagesAsync(IPage page)
@@ -260,5 +299,54 @@ private static void AssertCoreLibReadyToRun(string frameworkDir, bool expectRead
             else
                 Assert.Equal(0, tableSize);
         }
+
+        private void AssertCompositeReadyToRun(string frameworkDir)
+        {
+            string bootConfigPath = _provider.GetBootConfigPath(frameworkDir);
+            if (EnvironmentVariables.UseFingerprinting)
+            {
+                string indexPath = Path.Combine(Path.GetDirectoryName(frameworkDir)!, "index.html");
+                Match activeBoot = Regex.Match(File.ReadAllText(indexPath),
+                    @"""./_framework/dotnet\.js"": ""./_framework/(?<name>dotnet\.[a-z0-9]{10}\.js)""");
+                Assert.True(activeBoot.Success, $"Missing active dotnet.js import in '{indexPath}'.");
+                bootConfigPath = Path.Combine(frameworkDir, activeBoot.Groups["name"].Value);
+            }
+            AssetsData assets = (AssetsData)_provider.GetBootJson(bootConfigPath).resources;
+            GeneralAsset composite = Assert.Single(assets.coreAssembly,
+                asset => asset.virtualPath?.EndsWith(".r2r.wasm", System.StringComparison.Ordinal) == true);
+            Assert.Equal("BlazorBasicTestApp.r2r.wasm", composite.virtualPath);
+            if (EnvironmentVariables.UseFingerprinting)
+                Assert.Matches(@"^BlazorBasicTestApp\.r2r\.[a-z0-9]{10}\.wasm$", composite.name);
+            Assert.Contains(assets.coreAssembly,
+                asset => asset.virtualPath?.StartsWith("System.Private.CoreLib", System.StringComparison.Ordinal) == true);
+            Assert.Contains(assets.assembly,
+                asset => asset.virtualPath == "R2rSuffixLibrary.r2r.wasm");
+            Assert.DoesNotContain(assets.assembly,
+                asset => asset.virtualPath == composite.virtualPath);
+
+            string compositePath = Path.Combine(frameworkDir, composite.name);
+            using FileStream stream = File.OpenRead(compositePath);
+            Assert.True(WebcilReader.TryReadWebcilInWasmSizes(stream, out _, out int tableSize, out string? failureReason), failureReason);
+            Assert.True(tableSize > 0, $"Expected compiled methods in '{compositePath}'.");
+            Assert.True(Directory.EnumerateFiles(frameworkDir, "System.Private.CoreLib*.wasm").Any(),
+                $"Expected a component stub for System.Private.CoreLib in '{frameworkDir}'.");
+        }
+
+        private static void AddR2RSuffixLibrary(ProjectInfo info)
+        {
+            string appDirectory = Path.GetDirectoryName(info.ProjectFilePath)!;
+            string libraryDirectory = Path.GetFullPath(Path.Combine(appDirectory, "..", "R2rSuffixLibrary"));
+            Directory.CreateDirectory(libraryDirectory);
+            File.WriteAllText(Path.Combine(libraryDirectory, "R2rSuffixLibrary.csproj"), $$"""
+                <Project Sdk="Microsoft.NET.Sdk">
+                  <PropertyGroup>
+                    <TargetFramework>{{DefaultTargetFrameworkForBlazor}}</TargetFramework>
+                    <AssemblyName>R2rSuffixLibrary.r2r</AssemblyName>
+                  </PropertyGroup>
+                </Project>
+                """);
+            File.WriteAllText(Path.Combine(libraryDirectory, "Marker.cs"),
+                "public static class R2rSuffixLibraryMarker { public static int Value => 42; }");
+        }
     }
 }
diff --git a/src/native/libs/Common/JavaScript/host/host.ts b/src/native/libs/Common/JavaScript/host/host.ts
index 26f2b7ad9f0dcc..25fa932f605d54 100644
--- a/src/native/libs/Common/JavaScript/host/host.ts
+++ b/src/native/libs/Common/JavaScript/host/host.ts
@@ -24,7 +24,9 @@ export function initializeCoreCLR(): number {
     }
 
     const assemblyPaths = loaderConfig.resources!.assembly.map(asset => asset.virtualPath.replace(/\.wasm$/, ".dll"));
-    const coreAssemblyPaths = loaderConfig.resources!.coreAssembly.map(asset => asset.virtualPath.replace(/\.wasm$/, ".dll"));
+    const coreAssemblyPaths = loaderConfig.resources!.coreAssembly
+        .filter(asset => !asset.virtualPath.endsWith(".r2r.wasm"))
+        .map(asset => asset.virtualPath.replace(/\.wasm$/, ".dll"));
     const tpa = [...coreAssemblyPaths, ...assemblyPaths].join(":");
     runtimeConfigProperties.set(HOST_PROPERTY_TRUSTED_PLATFORM_ASSEMBLIES, tpa);
     runtimeConfigProperties.set(HOST_PROPERTY_NATIVE_DLL_SEARCH_DIRECTORIES, loaderConfig.virtualWorkingDirectory!);
diff --git a/src/native/libs/Common/JavaScript/loader/assets.ts b/src/native/libs/Common/JavaScript/loader/assets.ts
index eaf4508a140905..90358722faf61d 100644
--- a/src/native/libs/Common/JavaScript/loader/assets.ts
+++ b/src/native/libs/Common/JavaScript/loader/assets.ts
@@ -149,6 +149,14 @@ export async function fetchIcu(asset: IcuAsset): Promise<void> {
 }
 
 export async function fetchAssembly(asset: AssemblyAsset): Promise<void> {
+    return fetchAssemblyInternal(asset, false);
+}
+
+export async function fetchCoreAssembly(asset: AssemblyAsset): Promise<void> {
+    return fetchAssemblyInternal(asset, true);
+}
+
+async function fetchAssemblyInternal(asset: AssemblyAsset, isCoreAssembly: boolean): Promise<void> {
     const assetInternal = asset as AssetEntryInternal;
     totalAssetsToDownload++;
     dotnetAssert.check(assetInternal.virtualPath, "Assembly asset must have virtualPath");
@@ -160,7 +168,7 @@ export async function fetchAssembly(asset: AssemblyAsset): Promise<void> {
     }
 
     const isWebcilInWasm = assetInternal.virtualPath?.endsWith(".wasm") ?? false;
-    normalizeVirtualPath(assetInternal);
+    normalizeVirtualPath(assetInternal, isCoreAssembly && assetInternal.virtualPath.endsWith(".r2r.wasm"));
 
     if (isWebcilInWasm) {
         await fetchWebcil(assetInternal);
@@ -563,9 +571,12 @@ export function verifyAllAssetsDownloaded(): void {
     dotnetAssert.check(downloadedAssetsCount === totalAssetsToDownload, `Not all assets were downloaded. Downloaded ${downloadedAssetsCount} out of ${totalAssetsToDownload}`);
 }
 
-function normalizeVirtualPath(asset: AssetEntryInternal): void {
+function normalizeVirtualPath(asset: AssetEntryInternal, preserveWasmExtension: boolean = false): void {
     dotnetAssert.check(asset.virtualPath, "Asset must have virtualPath");
-    asset.virtualPath = asset.virtualPath!.replace(/\.wasm$/, ".dll");
+    // Composite R2R images are probed by their .r2r.wasm name, not as managed .dll assemblies.
+    if (!preserveWasmExtension) {
+        asset.virtualPath = asset.virtualPath!.replace(/\.wasm$/, ".dll");
+    }
     asset.virtualPath = asset.virtualPath.startsWith("/")
         ? asset.virtualPath
         : asset.culture
diff --git a/src/native/libs/Common/JavaScript/loader/run.ts b/src/native/libs/Common/JavaScript/loader/run.ts
index 6604334d3ce51e..c2c70435840c44 100644
--- a/src/native/libs/Common/JavaScript/loader/run.ts
+++ b/src/native/libs/Common/JavaScript/loader/run.ts
@@ -8,7 +8,7 @@ import { exit, runtimeState } from "./exit";
 import { createPromiseCompletionSource } from "./promise-completion-source";
 import { getIcuResourceName } from "./icu";
 import { loaderConfig, validateLoaderConfig } from "./config";
-import { fetchAssembly, fetchIcu, fetchNativeSymbols, fetchPdb, fetchSatelliteAssemblies, fetchVfs, fetchMainWasm, loadDotnetModule, loadJSModule, nativeModulePromiseController, verifyAllAssetsDownloaded, callLibraryInitializerOnRuntimeReady, callLibraryInitializerOnRuntimeConfigLoaded, prefetchAllResources, prefetchJSModuleLinks, resolveAllDownloadsQueued } from "./assets";
+import { fetchAssembly, fetchCoreAssembly, fetchIcu, fetchNativeSymbols, fetchPdb, fetchSatelliteAssemblies, fetchVfs, fetchMainWasm, loadDotnetModule, loadJSModule, nativeModulePromiseController, verifyAllAssetsDownloaded, callLibraryInitializerOnRuntimeReady, callLibraryInitializerOnRuntimeConfigLoaded, prefetchAllResources, prefetchJSModuleLinks, resolveAllDownloadsQueued } from "./assets";
 import { initPolyfillsLoader } from "./polyfills";
 import { validateEngineFeatures } from "./bootstrap";
 
@@ -117,7 +117,7 @@ export async function createRuntime(downloadOnly: boolean, httpCacheOnly: boolea
         const runtimeModulePromise: Promise<JsModuleExports> = loadDotnetModule(resources.jsModuleRuntime[0]);
         const wasmNativePromise: Promise<Response> = fetchMainWasm(resources.wasmNative[0]);
 
-        const coreAssembliesPromise = forEachResource(resources.coreAssembly, fetchAssembly);
+        const coreAssembliesPromise = forEachResource(resources.coreAssembly, fetchCoreAssembly);
 
         const icuResourceName = getIcuResourceName();
         const icuDataPromise = forEachResource(resources.icu, fetchIcu, asset => asset.name === icuResourceName);
diff --git a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs
index 90e5608d8d7bc7..41e864feb49d5c 100644
--- a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs
+++ b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs
@@ -292,6 +292,13 @@ private void WriteBootConfig(string entryAssemblyName)
                         }
                     }
                 }
+                else if (string.Equals("WasmResource", assetTraitName, StringComparison.OrdinalIgnoreCase)
+                    && string.Equals("core", assetTraitValue, StringComparison.OrdinalIgnoreCase))
+                {
+                    MapFingerprintedAsset(resourceData, resourceRoute, resourceName);
+                    Log.LogMessage(MessageImportance.Low, "Candidate '{0}' is defined as a core assembly.", resource.ItemSpec);
+                    resourceList = resourceData.coreAssembly;
+                }
                 else if (string.Equals("runtime", assetTraitValue, StringComparison.OrdinalIgnoreCase))
                 {
                     MapFingerprintedAsset(resourceData, resourceRoute, resourceName);

From 3df1ea384d60c5ca3b49bbcfdf8bc8d21388c127 Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Thu, 24 Sep 2026 16:55:56 -0500
Subject: [PATCH 02/11] [wasm][coreclr] Single-source composite owner identity
 in the loader

The loader now decides once, while fetching resources.coreAssembly, whether
an asset is the composite ReadyToRun owner and records it on the asset; the
host builds the TPA from that flag instead of re-deriving it from the
.r2r.wasm suffix.

The composite test app now calls into the referenced R2rSuffixLibrary.r2r
at startup and asserts it loaded, so an ordinary library whose name ends in
.r2r is verified to load as a managed component rather than only checked in
the boot manifest.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../wasm/Wasm.Build.Tests/ReadyToRunTests.cs     | 16 ++++++++++++++--
 src/native/libs/Common/JavaScript/host/host.ts   |  4 ++--
 .../libs/Common/JavaScript/loader/assets.ts      | 11 +++++++----
 .../libs/Common/JavaScript/types/internal.ts     |  1 +
 4 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
index 7ab5a726df92d1..11a125ba92ef78 100644
--- a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
@@ -80,7 +80,7 @@ private async Task PublishRunAllPagesCore(Configuration config, bool trimmed, bo
             // is a per-app image, not the runtime pack's. nativeRelink also relinks dotnet.native.wasm.
             string label = $"r2r_pub_{(trimmed ? "trim" : "notrim")}{(nativeRelink ? "_native" : "")}{(composite ? "_composite" : "")}";
             string extraItems = composite
-                ? """<ProjectReference Include="../R2rSuffixLibrary/R2rSuffixLibrary.csproj" /><TrimmerRootAssembly Include="R2rSuffixLibrary.r2r" />"""
+                ? """<ProjectReference Include="../R2rSuffixLibrary/R2rSuffixLibrary.csproj" />"""
                 : string.Empty;
             ProjectInfo info = CopyTestAsset(config, aot: false, TestAsset.BlazorBasicTestApp, label,
                 extraProperties: $"<PublishReadyToRun>true</PublishReadyToRun><PublishReadyToRunComposite>{(composite ? "true" : "false")}</PublishReadyToRunComposite><PublishTrimmed>{(trimmed ? "true" : "false")}</PublishTrimmed>",
@@ -118,9 +118,13 @@ private async Task PublishRunAllPagesCore(Configuration config, bool trimmed, bo
                 AssertNoDuplicateAssemblies(frameworkDir);
             }
 
+            bool suffixLibraryLoaded = false;
             await RunForPublishWithWebServer(new BlazorRunOptions(config,
                 CheckCounter: false,
+                OnConsoleMessage: (_, msg) => suffixLibraryLoaded |= msg.Contains(SuffixLibraryLoadedMessage),
                 ExecuteAfterLoaded: (_, page) => InteractAllPagesAsync(page)));
+            if (composite)
+                Assert.True(suffixLibraryLoaded, $"'{SuffixLibraryLoadedMessage}' was not logged; R2rSuffixLibrary.r2r did not load as a component assembly.");
         }
 
         [ConditionalTheory(typeof(BuildTestBase), nameof(IsCoreClrRuntime))]
@@ -332,8 +336,16 @@ private void AssertCompositeReadyToRun(string frameworkDir)
                 $"Expected a component stub for System.Private.CoreLib in '{frameworkDir}'.");
         }
 
-        private static void AddR2RSuffixLibrary(ProjectInfo info)
+        private const string SuffixLibraryLoadedMessage = "Loaded R2rSuffixLibrary.r2r: 42";
+
+        // An ordinary library whose name ends in .r2r must still load as a managed component assembly,
+        // not be mistaken for the composite owner image (<entry>.r2r.wasm).
+        private void AddR2RSuffixLibrary(ProjectInfo info)
         {
+            UpdateFile("Program.cs", new Dictionary<string, string>
+            {
+                { "var builder", "System.Console.WriteLine($\"Loaded {typeof(R2rSuffixLibraryMarker).Assembly.GetName().Name}: {R2rSuffixLibraryMarker.Value}\");\nvar builder" }
+            });
             string appDirectory = Path.GetDirectoryName(info.ProjectFilePath)!;
             string libraryDirectory = Path.GetFullPath(Path.Combine(appDirectory, "..", "R2rSuffixLibrary"));
             Directory.CreateDirectory(libraryDirectory);
diff --git a/src/native/libs/Common/JavaScript/host/host.ts b/src/native/libs/Common/JavaScript/host/host.ts
index 25fa932f605d54..dfb9fb7d0977ff 100644
--- a/src/native/libs/Common/JavaScript/host/host.ts
+++ b/src/native/libs/Common/JavaScript/host/host.ts
@@ -1,7 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-import type { CharPtrPtr, VoidPtr } from "../types";
+import type { AssetEntryInternal, CharPtrPtr, VoidPtr } from "../types";
 import { _ems_ } from "../ems-ambient";
 import { browserVirtualAppBase, sizeOfPtr } from "../per-module";
 
@@ -25,7 +25,7 @@ export function initializeCoreCLR(): number {
 
     const assemblyPaths = loaderConfig.resources!.assembly.map(asset => asset.virtualPath.replace(/\.wasm$/, ".dll"));
     const coreAssemblyPaths = loaderConfig.resources!.coreAssembly
-        .filter(asset => !asset.virtualPath.endsWith(".r2r.wasm"))
+        .filter(asset => !(asset as AssetEntryInternal).isCompositeImage)
         .map(asset => asset.virtualPath.replace(/\.wasm$/, ".dll"));
     const tpa = [...coreAssemblyPaths, ...assemblyPaths].join(":");
     runtimeConfigProperties.set(HOST_PROPERTY_TRUSTED_PLATFORM_ASSEMBLIES, tpa);
diff --git a/src/native/libs/Common/JavaScript/loader/assets.ts b/src/native/libs/Common/JavaScript/loader/assets.ts
index 90358722faf61d..839cc6e9768f68 100644
--- a/src/native/libs/Common/JavaScript/loader/assets.ts
+++ b/src/native/libs/Common/JavaScript/loader/assets.ts
@@ -168,7 +168,11 @@ async function fetchAssemblyInternal(asset: AssemblyAsset, isCoreAssembly: boole
     }
 
     const isWebcilInWasm = assetInternal.virtualPath?.endsWith(".wasm") ?? false;
-    normalizeVirtualPath(assetInternal, isCoreAssembly && assetInternal.virtualPath.endsWith(".r2r.wasm"));
+    // The SDK places only System.Private.CoreLib and the composite R2R owner in coreAssembly. Crossgen2 names
+    // the owner <entry>.r2r.wasm and every component stub probes for it by that exact name, so it keeps its
+    // .wasm virtual path and is not a managed assembly (see initializeCoreCLR's TPA).
+    assetInternal.isCompositeImage = isCoreAssembly && assetInternal.virtualPath.endsWith(".r2r.wasm");
+    normalizeVirtualPath(assetInternal);
 
     if (isWebcilInWasm) {
         await fetchWebcil(assetInternal);
@@ -571,10 +575,9 @@ export function verifyAllAssetsDownloaded(): void {
     dotnetAssert.check(downloadedAssetsCount === totalAssetsToDownload, `Not all assets were downloaded. Downloaded ${downloadedAssetsCount} out of ${totalAssetsToDownload}`);
 }
 
-function normalizeVirtualPath(asset: AssetEntryInternal, preserveWasmExtension: boolean = false): void {
+function normalizeVirtualPath(asset: AssetEntryInternal): void {
     dotnetAssert.check(asset.virtualPath, "Asset must have virtualPath");
-    // Composite R2R images are probed by their .r2r.wasm name, not as managed .dll assemblies.
-    if (!preserveWasmExtension) {
+    if (!asset.isCompositeImage) {
         asset.virtualPath = asset.virtualPath!.replace(/\.wasm$/, ".dll");
     }
     asset.virtualPath = asset.virtualPath.startsWith("/")
diff --git a/src/native/libs/Common/JavaScript/types/internal.ts b/src/native/libs/Common/JavaScript/types/internal.ts
index 7307d336ee6772..9569ab37c07d54 100644
--- a/src/native/libs/Common/JavaScript/types/internal.ts
+++ b/src/native/libs/Common/JavaScript/types/internal.ts
@@ -65,6 +65,7 @@ export interface AssetEntryInternal extends AssetEntry {
     inprogress?: boolean
     tableSize?: number
     payloadSize?: number
+    isCompositeImage?: boolean
 }
 
 export type LoaderConfigInternal = LoaderConfig & {

From 8e5939f6d072a1b833ddddd979c18ae2b6608454 Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Fri, 25 Sep 2026 09:42:18 -0500
Subject: [PATCH 03/11] Require wasm-aware ReadyToRun tasks for browser
 composite

Stock SDK ReadyToRun tasks name the browser composite owner '<entry>.r2r.dll'
and plan component outputs as '<name>.dll', while crossgen2 emits
'<entry>.r2r.wasm' plus '<name>.wasm' stubs. Fail fast with an actionable
error instead of a downstream ConvertDllsToWebcil file-not-found.

Ship the Crossgen2Tasks shim to BuildWasmApps Helix payloads and use it only
for composite Wasm.Build.Tests so per-assembly R2R keeps stock SDK coverage.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 src/libraries/sendtohelix-browser.targets     |  5 +++--
 ...ET.Sdk.WebAssembly.Browser.CoreCLR.targets | 13 ++++++++++++
 .../wasm/Wasm.Build.Tests/ReadyToRunTests.cs  | 21 ++++++++++---------
 3 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/src/libraries/sendtohelix-browser.targets b/src/libraries/sendtohelix-browser.targets
index 4762716bdfc717..224027c11aee34 100644
--- a/src/libraries/sendtohelix-browser.targets
+++ b/src/libraries/sendtohelix-browser.targets
@@ -295,8 +295,9 @@
          from the SDK crossgen2 pack (which the SDK restores when PublishReadyToRun is set), so it is only shipped
          as a correlation payload when the in-build crossgen2 is present in this leg (dev/in-tree). The shim ships
          whenever it is built - it is gated on its own path, not on the crossgen2 bin dir, which the WBT test leg
-         does not carry. -->
-    <ItemGroup Condition="'$(NeedsEMSDK)' == 'true' and '$(RuntimeFlavor)' == 'CoreCLR' and Exists('$(ArtifactsBinDir)Crossgen2Tasks\$(TasksConfiguration)\')">
+         does not carry. Wasm.Build.Tests (BuildWasmApps) need it for PublishReadyToRunComposite, whose output
+         naming the base SDK's ReadyToRun tasks don't implement yet. -->
+    <ItemGroup Condition="('$(NeedsEMSDK)' == 'true' or '$(Scenario)' == 'BuildWasmApps') and '$(RuntimeFlavor)' == 'CoreCLR' and Exists('$(ArtifactsBinDir)Crossgen2Tasks\$(TasksConfiguration)\')">
       <HelixCorrelationPayload Include="$(ArtifactsBinDir)Crossgen2Tasks\$(TasksConfiguration)\"
                                Destination="Crossgen2Tasks/$(Configuration)" />
     </ItemGroup>
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
index 159fa921ddd56b..99e69165211f10 100644
--- 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
@@ -65,6 +65,19 @@ Copyright (c) .NET Foundation. All rights reserved.
            Text="PublishReadyToRun=true for CoreCLR browser-wasm requires a wasm-capable crossgen2, but none was resolved. Set Crossgen2InBuildDir to an in-build crossgen2 directory (or provide a ResolvedCrossgen2Pack) until wasm crossgen2 support flows through the base SDK (dotnet/sdk#55785)." />
   </Target>
 
+  <!-- Composite needs wasm-aware ReadyToRun tasks: the component stubs probe for the owner as <entry>.r2r.wasm,
+       and crossgen2 writes each component stub as <name>.wasm. Tasks without wasm naming plan <entry>.r2r.dll
+       and <name>.dll outputs that are never produced, so fail before the (long) composite compile. -->
+  <Target Name="_WasmCoreClrValidateCompositeTasks"
+          Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' == 'true'"
+          BeforeTargets="_CreateR2RImages">
+    <ItemGroup>
+      <_WasmCompositeOwnerEntry Include="@(_ReadyToRunCompileList->WithMetadataValue('CreateCompositeImage', 'true'))" />
+    </ItemGroup>
+    <Error Condition="'@(_WasmCompositeOwnerEntry)' != '' and !$([System.String]::Copy('%(_WasmCompositeOwnerEntry.OutputR2RImage)').EndsWith('.r2r.wasm'))"
+           Text="PublishReadyToRunComposite for CoreCLR browser-wasm requires ReadyToRun SDK tasks that name the composite image '&lt;entry&gt;.r2r.wasm', but they planned '$([System.IO.Path]::GetFileName('%(_WasmCompositeOwnerEntry.OutputR2RImage)'))'. Use an SDK with wasm ReadyToRun output naming (dotnet/sdk#56395), or set Crossgen2SdkOverridePropsPath and Crossgen2SdkOverrideTargetsPath to the dotnet/runtime Crossgen2Tasks." />
+  </Target>
+
   <!-- PublishTrimmed selects the staged closure (untrimmed pack vs linker output) exactly like
        PublishReadyToRun selects its flavour, so it belongs in the webcil staging stamp too. -->
   <ItemGroup>
diff --git a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
index 11a125ba92ef78..b801ae4d708c6d 100644
--- a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
@@ -87,7 +87,7 @@ private async Task PublishRunAllPagesCore(Configuration config, bool trimmed, bo
                 extraItems: extraItems);
             if (composite)
                 AddR2RSuffixLibrary(info);
-            string extraArgs = GetR2RBuildArgs(config);
+            string extraArgs = GetR2RBuildArgs(config, composite);
             if (nativeRelink)
             {
                 // CoreCLR relinks dotnet.native.wasm via the in-tree targets + EMSDK_PATH, not the browser
@@ -148,7 +148,7 @@ public void CompositeRequiresWebcil(Configuration config)
             ProjectInfo info = CopyTestAsset(config, aot: false, TestAsset.BlazorBasicTestApp, "r2r_composite_no_webcil",
                 extraProperties: "<PublishReadyToRun>true</PublishReadyToRun><PublishReadyToRunComposite>true</PublishReadyToRunComposite><WasmEnableWebcil>false</WasmEnableWebcil>");
             (string _, string output) = BlazorPublish(info, config,
-                new PublishOptions(ExpectSuccess: false, ExtraMSBuildArgs: GetR2RBuildArgs(config)));
+                new PublishOptions(ExpectSuccess: false, ExtraMSBuildArgs: GetR2RBuildArgs(config, composite: true)));
 
             Assert.Contains("PublishReadyToRunComposite for CoreCLR browser-wasm requires WebCIL-in-Wasm assemblies", output);
         }
@@ -262,12 +262,13 @@ private void AssertPerAppCrossgenRan(Configuration config, bool expected)
                 Assert.True(imageCount == 0, $"Expected no per-app crossgen2 output, found {imageCount} file(s) under '{r2rDir}'.");
         }
 
-        // Wire the wasm-aware Crossgen2Tasks shim (the wasm-container crossgen tasks) so R2R images use the
-        // right container, and the in-build crossgen2 when this leg shipped it. Each is passed only when present
-        // under BASE_DIR: the no-workload leg ships the shim but resolves crossgen2 itself from the SDK pack (the
-        // SDK restores it when PublishReadyToRun is set), so passing a non-existent Crossgen2InBuildDir there
-        // would break the call-helpers generator. All inert if BASE_DIR is unset.
-        private static string GetR2RBuildArgs(Configuration config)
+        // Wire the in-build crossgen2 when this leg shipped it, and for composite the wasm-aware Crossgen2Tasks shim:
+        // composite needs the shim's wasm output naming (<entry>.r2r.wasm owner, <name>.wasm stubs), which the base
+        // SDK's ReadyToRun tasks don't implement yet (dotnet/sdk#56395). Per-assembly R2R keeps the base SDK tasks so
+        // that path stays covered. Each is passed only when present under BASE_DIR: the no-workload leg resolves
+        // crossgen2 itself from the SDK pack (the SDK restores it when PublishReadyToRun is set), so passing a
+        // non-existent Crossgen2InBuildDir there would break the call-helpers generator. All inert if BASE_DIR is unset.
+        private static string GetR2RBuildArgs(Configuration config, bool composite)
         {
             string? baseDir = EnvironmentVariables.BaseDir;
             if (string.IsNullOrEmpty(baseDir))
@@ -282,9 +283,9 @@ private static string GetR2RBuildArgs(Configuration config)
             var args = new List<string>();
             if (Directory.Exists(crossgenDir))
                 args.Add($"-p:Crossgen2InBuildDir=\"{crossgenDir}\"");
-            if (File.Exists(shimProps))
+            if (composite && File.Exists(shimProps))
                 args.Add($"-p:Crossgen2SdkOverridePropsPath=\"{shimProps}\"");
-            if (File.Exists(shimTargets))
+            if (composite && File.Exists(shimTargets))
                 args.Add($"-p:Crossgen2SdkOverrideTargetsPath=\"{shimTargets}\"");
             return string.Join(" ", args);
         }

From 942f63586a8d15d8d02bd2afeba9a9b20683fe29 Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Fri, 25 Sep 2026 11:56:06 -0500
Subject: [PATCH 04/11] Address wasm composite R2R review feedback

- Boot config: flag the composite owner with isCompositeImage (new
  WasmResource/readyToRunComposite trait) instead of the loader inferring it
  from the .r2r.wasm file name.
- Define the composite owner static web asset with DefineStaticWebAssets
  rather than a hand-built candidate.
- Stale-prune keeps what crossgen2 actually emitted (compile outputs plus
  composite component stubs), not the task's publish plan.
- Move R2rSuffixLibrary into testassets; GetBootConfigPath picks the newest
  fingerprinted dotnet.js so composite assertions use the shared helper.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 ...ET.Sdk.WebAssembly.Browser.CoreCLR.targets |  7 ++-
 ...rosoft.NET.Sdk.WebAssembly.Browser.targets | 45 +++++++------
 .../Wasm.Build.Tests/ProjectProviderBase.cs   | 10 ++-
 .../wasm/Wasm.Build.Tests/ReadyToRunTests.cs  | 63 ++++++-------------
 .../R2rSuffixLibrary/R2rSuffixLibrary.csproj  |  9 +++
 .../R2rSuffixLibraryMarker.cs                 |  7 +++
 .../libs/Common/JavaScript/loader/assets.ts   | 14 +----
 .../libs/Common/JavaScript/loader/run.ts      |  4 +-
 .../Common/JavaScript/types/public-api.ts     |  5 ++
 .../BootJsonBuilderHelper.cs                  |  5 +-
 .../BootJsonData.cs                           |  8 +++
 .../GenerateWasmBootJson.cs                   |  9 ++-
 12 files changed, 102 insertions(+), 84 deletions(-)
 create mode 100644 src/mono/wasm/testassets/BlazorBasicTestApp/R2rSuffixLibrary/R2rSuffixLibrary.csproj
 create mode 100644 src/mono/wasm/testassets/BlazorBasicTestApp/R2rSuffixLibrary/R2rSuffixLibraryMarker.cs

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
index 99e69165211f10..041760b179402b 100644
--- 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
@@ -243,10 +243,15 @@ Copyright (c) .NET Foundation. All rights reserved.
           DependsOnTargets="_WasmCoreClrSelectR2RDirectories"
           AfterTargets="_CreateR2RImages">
     <ItemGroup Condition="'$(_WasmPublishR2RDir)' != '' and Exists('$(_WasmPublishR2RDir)')">
+      <!-- Keep what crossgen2 actually emitted, not the task's publish plan: every compiled image, plus in
+           composite mode a <name>.wasm component stub beside the owner for each composite input. -->
+      <_WasmEmittedPerAppR2R Include="@(_ReadyToRunCompileList->'%(OutputR2RImage)')" />
+      <_WasmEmittedPerAppR2R Include="@(_ReadyToRunCompositeBuildInput->'$(_WasmPublishR2RDir)%(FileName).wasm');@(_ReadyToRunCompositeUnrootedBuildInput->'$(_WasmPublishR2RDir)%(FileName).wasm')"
+                             Condition="'$(PublishReadyToRunComposite)' == 'true'" />
       <!-- Both extensions: ConvertDll probes PrebuiltR2RDirectory for .dll before .wasm (a stock SDK names the
            R2R output <name>.dll), so a surviving .dll would win the probe over the current .wasm. -->
       <_WasmStalePerAppR2R Include="$(_WasmPublishR2RDir)*.wasm;$(_WasmPublishR2RDir)*.dll"
-                           Exclude="@(_ReadyToRunFilesToPublish)" />
+                           Exclude="@(_WasmEmittedPerAppR2R)" />
     </ItemGroup>
     <Delete Files="@(_WasmStalePerAppR2R)" />
   </Target>
diff --git a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
index 2710416f5efa3d..456a4fcac12d53 100644
--- a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
+++ b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
@@ -1062,25 +1062,32 @@ Copyright (c) .NET Foundation. All rights reserved.
     <ItemGroup Condition="'$(UseMonoRuntime)' == 'false' and '$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' == 'true'">
       <_WasmCompositeCompilation Include="@(_ReadyToRunCompileList)"
                                  Condition="'%(CreateCompositeImage)' == 'true'" />
-      <_WasmCompositePublishCandidate Include="@(_WasmCompositeCompilation->'%(OutputR2RImage)')">
-        <SourceId>$(PackageId)</SourceId>
-        <SourceType>Computed</SourceType>
-        <ContentRoot>$([MSBuild]::NormalizeDirectory($(PublishDir), 'wwwroot'))</ContentRoot>
-        <BasePath>$(StaticWebAssetBasePath)</BasePath>
-        <RelativePath Condition="'$(_WasmFingerprintAssets)' != 'true'">_framework/$([System.IO.Path]::GetFileName('%(OutputR2RImage)'))</RelativePath>
-        <RelativePath Condition="'$(_WasmFingerprintAssets)' == 'true'">_framework/$([System.IO.Path]::GetFileNameWithoutExtension('%(OutputR2RImage)'))#[.{fingerprint}]!.wasm</RelativePath>
-        <AssetKind>Publish</AssetKind>
-        <AssetMode>All</AssetMode>
-        <AssetRole>Primary</AssetRole>
-        <AssetTraitName>WasmResource</AssetTraitName>
-        <AssetTraitValue>core</AssetTraitValue>
-        <CopyToOutputDirectory>Never</CopyToOutputDirectory>
-        <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
-        <OriginalItemSpec>%(OutputR2RImage)</OriginalItemSpec>
-      </_WasmCompositePublishCandidate>
+      <_WasmCompositePublishCandidate Include="@(_WasmCompositeCompilation->'%(OutputR2RImage)')" KeepMetadata="OutputR2RImage" />
+      <_WasmCompositePublishCandidate Update="@(_WasmCompositePublishCandidate)"
+                                      ContentRoot="%(RootDir)%(Directory)"
+                                      RelativePath="_framework/%(FileName)%(Extension)" />
+      <_WasmCompositeFingerprintPattern Include="WasmFiles" Pattern="*.wasm" Expression="#[.{fingerprint}]!" />
     </ItemGroup>
     <Error Condition="'$(UseMonoRuntime)' == 'false' and '$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' == 'true' and '@(_WasmCompositePublishCandidate)' == ''"
            Text="Composite ReadyToRun compilation did not produce a composite WebAssembly image." />
+    <!-- The composite owner is not a managed assembly, so it bypasses ComputeWasmPublishAssets/ConvertDllsToWebcil.
+         The readyToRunComposite trait routes it to coreAssembly with isCompositeImage set in the boot config. -->
+    <DefineStaticWebAssets Condition="'@(_WasmCompositePublishCandidate)' != ''"
+      CandidateAssets="@(_WasmCompositePublishCandidate)"
+      SourceId="$(PackageId)"
+      SourceType="Computed"
+      BasePath="$(StaticWebAssetBasePath)"
+      AssetKind="Publish"
+      AssetMode="All"
+      AssetRole="Primary"
+      AssetTraitName="WasmResource"
+      AssetTraitValue="readyToRunComposite"
+      CopyToOutputDirectory="Never"
+      CopyToPublishDirectory="PreserveNewest"
+      FingerprintCandidates="$(_WasmFingerprintAssets)"
+      FingerprintPatterns="@(_WasmCompositeFingerprintPattern)">
+      <Output TaskParameter="Assets" ItemName="_WasmCompositePublishStaticWebAsset" />
+    </DefineStaticWebAssets>
 
     <ItemGroup Condition="'$(_WasmInlineBootConfig)' == 'true'">
       <_WasmDotnetJsForPublish Include="@(ResolvedFileToPublish)" Condition="'%(FileName)%(Extension)' == 'dotnet.js'" />
@@ -1126,7 +1133,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     -->
     <ItemGroup>
       <_NewWebcilPublishStaticWebAssetsCandidatesNoMetadata
-        Include="@(_NewWebcilPublishStaticWebAssetsCandidates);@(_WasmCompositePublishCandidate)"
+        Include="@(_NewWebcilPublishStaticWebAssetsCandidates)"
         RemoveMetadata="Integrity;Fingerprint" />
       <!-- Set per-item ContentRoot so each asset's Identity matches its actual file on disk.
            Clear stale Fingerprint/Integrity so DefineStaticWebAssets recomputes from the actual file. -->
@@ -1147,7 +1154,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     </DefineStaticWebAssets>
 
     <DefineStaticWebAssetEndpoints
-      CandidateAssets="@(_NewWebcilPublishStaticWebAssets)"
+      CandidateAssets="@(_NewWebcilPublishStaticWebAssets);@(_WasmCompositePublishStaticWebAsset)"
       ExistingEndpoints="@(StaticWebAssetEndpoint)"
       ContentTypeMappings="@(StaticWebAssetContentTypeMapping)"
     >
@@ -1156,7 +1163,7 @@ Copyright (c) .NET Foundation. All rights reserved.
 
     <ItemGroup>
       <ResolvedFileToPublish Remove="@(_PublishResolvedFilesToRemove)" />
-      <StaticWebAsset Include="@(_NewWebcilPublishStaticWebAssets)" />
+      <StaticWebAsset Include="@(_NewWebcilPublishStaticWebAssets);@(_WasmCompositePublishStaticWebAsset)" />
       <StaticWebAssetEndpoint Include="@(_NewWebcilPublishStaticWebAssetsEndpoint)" />
 
       <!-- TODO: Probably doesn't do anything as of now, original https://github.com/dotnet/aspnetcore/pull/34798 -->
diff --git a/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs b/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs
index ccd4b435dc5253..ba9e8f3e8bd39b 100644
--- a/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs
@@ -560,9 +560,11 @@ public string GetBootConfigPath(string binFrameworkDir, string? bootConfigFileNa
         {
             string bootFileNameWithoutExtension = Path.GetFileNameWithoutExtension(bootConfigFileName);
             string bootFileExtension = Path.GetExtension(bootConfigFileName);
+            // A republish into an existing output leaves the previous fingerprinted copy beside the current one;
+            // pick the newest, as FindAndAssertDotnetFiles does, so assertions read the active boot config.
             string? fingerprintedBootJsonPath = Directory
                 .EnumerateFiles(binFrameworkDir)
-                .FirstOrDefault(f =>
+                .Where(f =>
                 {
                     if (Path.GetExtension(f) != bootFileExtension)
                         return false;
@@ -575,8 +577,10 @@ public string GetBootConfigPath(string binFrameworkDir, string? bootConfigFileNa
                         return false;
 
                     return true;
-                });
-            
+                })
+                .OrderByDescending(File.GetLastWriteTimeUtc)
+                .FirstOrDefault();
+
             if (fingerprintedBootJsonPath == null)
                 throw new XunitException($"Could not find boot config '{bootConfigFileName}' with fingerprint in '{binFrameworkDir}'");
 
diff --git a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
index b801ae4d708c6d..2980d817eb409f 100644
--- a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
@@ -86,7 +86,7 @@ private async Task PublishRunAllPagesCore(Configuration config, bool trimmed, bo
                 extraProperties: $"<PublishReadyToRun>true</PublishReadyToRun><PublishReadyToRunComposite>{(composite ? "true" : "false")}</PublishReadyToRunComposite><PublishTrimmed>{(trimmed ? "true" : "false")}</PublishTrimmed>",
                 extraItems: extraItems);
             if (composite)
-                AddR2RSuffixLibrary(info);
+                LogR2RSuffixLibraryMarker();
             string extraArgs = GetR2RBuildArgs(config, composite);
             if (nativeRelink)
             {
@@ -290,76 +290,53 @@ private static string GetR2RBuildArgs(Configuration config, bool composite)
             return string.Join(" ", args);
         }
 
+        private static int GetReadyToRunTableSize(string webcilPath)
+        {
+            using FileStream stream = File.OpenRead(webcilPath);
+            Assert.True(WebcilReader.TryReadWebcilInWasmSizes(stream, out _, out int tableSize, out string? failureReason), failureReason);
+            return tableSize;
+        }
+
         private static void AssertCoreLibReadyToRun(string frameworkDir, bool expectReadyToRun)
         {
             string? coreLib = Directory.EnumerateFiles(frameworkDir, "System.Private.CoreLib*.wasm").FirstOrDefault();
             Assert.True(coreLib is not null, $"Expected a System.Private.CoreLib webcil under '{frameworkDir}'.");
 
-            using FileStream stream = File.OpenRead(coreLib!);
-            bool ok = WebcilReader.TryReadWebcilInWasmSizes(stream, out _, out int tableSize, out string? failureReason);
-            Assert.True(ok, failureReason);
-
+            int tableSize = GetReadyToRunTableSize(coreLib!);
             if (expectReadyToRun)
                 Assert.True(tableSize > 0, $"Expected a ReadyToRun table in '{coreLib}', but the R2R table size was 0.");
             else
                 Assert.Equal(0, tableSize);
         }
 
+        // The boot config flags exactly the composite owner, delivered via coreAssembly under its crossgen2 name so
+        // component stubs can probe for it; an assembly merely named *.r2r stays an ordinary, unflagged assembly.
         private void AssertCompositeReadyToRun(string frameworkDir)
         {
-            string bootConfigPath = _provider.GetBootConfigPath(frameworkDir);
-            if (EnvironmentVariables.UseFingerprinting)
-            {
-                string indexPath = Path.Combine(Path.GetDirectoryName(frameworkDir)!, "index.html");
-                Match activeBoot = Regex.Match(File.ReadAllText(indexPath),
-                    @"""./_framework/dotnet\.js"": ""./_framework/(?<name>dotnet\.[a-z0-9]{10}\.js)""");
-                Assert.True(activeBoot.Success, $"Missing active dotnet.js import in '{indexPath}'.");
-                bootConfigPath = Path.Combine(frameworkDir, activeBoot.Groups["name"].Value);
-            }
-            AssetsData assets = (AssetsData)_provider.GetBootJson(bootConfigPath).resources;
-            GeneralAsset composite = Assert.Single(assets.coreAssembly,
-                asset => asset.virtualPath?.EndsWith(".r2r.wasm", System.StringComparison.Ordinal) == true);
+            AssetsData assets = (AssetsData)_provider.GetBootJson(_provider.GetBootConfigPath(frameworkDir)).resources;
+            WebcilAsset composite = Assert.Single(assets.coreAssembly, asset => asset.isCompositeImage == true);
             Assert.Equal("BlazorBasicTestApp.r2r.wasm", composite.virtualPath);
             if (EnvironmentVariables.UseFingerprinting)
                 Assert.Matches(@"^BlazorBasicTestApp\.r2r\.[a-z0-9]{10}\.wasm$", composite.name);
+            Assert.DoesNotContain(assets.assembly, asset => asset.isCompositeImage == true);
             Assert.Contains(assets.coreAssembly,
                 asset => asset.virtualPath?.StartsWith("System.Private.CoreLib", System.StringComparison.Ordinal) == true);
-            Assert.Contains(assets.assembly,
-                asset => asset.virtualPath == "R2rSuffixLibrary.r2r.wasm");
-            Assert.DoesNotContain(assets.assembly,
-                asset => asset.virtualPath == composite.virtualPath);
+            Assert.Contains(assets.assembly, asset => asset.virtualPath == "R2rSuffixLibrary.r2r.wasm");
 
             string compositePath = Path.Combine(frameworkDir, composite.name);
-            using FileStream stream = File.OpenRead(compositePath);
-            Assert.True(WebcilReader.TryReadWebcilInWasmSizes(stream, out _, out int tableSize, out string? failureReason), failureReason);
-            Assert.True(tableSize > 0, $"Expected compiled methods in '{compositePath}'.");
+            Assert.True(GetReadyToRunTableSize(compositePath) > 0, $"Expected compiled methods in '{compositePath}'.");
             Assert.True(Directory.EnumerateFiles(frameworkDir, "System.Private.CoreLib*.wasm").Any(),
                 $"Expected a component stub for System.Private.CoreLib in '{frameworkDir}'.");
         }
 
         private const string SuffixLibraryLoadedMessage = "Loaded R2rSuffixLibrary.r2r: 42";
 
-        // An ordinary library whose name ends in .r2r must still load as a managed component assembly,
-        // not be mistaken for the composite owner image (<entry>.r2r.wasm).
-        private void AddR2RSuffixLibrary(ProjectInfo info)
-        {
-            UpdateFile("Program.cs", new Dictionary<string, string>
+        // Make the app call into the R2rSuffixLibrary test asset (referenced for composite runs) so the run proves
+        // it loaded as a component assembly rather than being mistaken for the composite owner.
+        private void LogR2RSuffixLibraryMarker()
+            => UpdateFile("Program.cs", new Dictionary<string, string>
             {
                 { "var builder", "System.Console.WriteLine($\"Loaded {typeof(R2rSuffixLibraryMarker).Assembly.GetName().Name}: {R2rSuffixLibraryMarker.Value}\");\nvar builder" }
             });
-            string appDirectory = Path.GetDirectoryName(info.ProjectFilePath)!;
-            string libraryDirectory = Path.GetFullPath(Path.Combine(appDirectory, "..", "R2rSuffixLibrary"));
-            Directory.CreateDirectory(libraryDirectory);
-            File.WriteAllText(Path.Combine(libraryDirectory, "R2rSuffixLibrary.csproj"), $$"""
-                <Project Sdk="Microsoft.NET.Sdk">
-                  <PropertyGroup>
-                    <TargetFramework>{{DefaultTargetFrameworkForBlazor}}</TargetFramework>
-                    <AssemblyName>R2rSuffixLibrary.r2r</AssemblyName>
-                  </PropertyGroup>
-                </Project>
-                """);
-            File.WriteAllText(Path.Combine(libraryDirectory, "Marker.cs"),
-                "public static class R2rSuffixLibraryMarker { public static int Value => 42; }");
-        }
     }
 }
diff --git a/src/mono/wasm/testassets/BlazorBasicTestApp/R2rSuffixLibrary/R2rSuffixLibrary.csproj b/src/mono/wasm/testassets/BlazorBasicTestApp/R2rSuffixLibrary/R2rSuffixLibrary.csproj
new file mode 100644
index 00000000000000..0d61c07c07f210
--- /dev/null
+++ b/src/mono/wasm/testassets/BlazorBasicTestApp/R2rSuffixLibrary/R2rSuffixLibrary.csproj
@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <!-- The .r2r assembly-name suffix must not be mistaken for a composite ReadyToRun owner image. -->
+  <PropertyGroup>
+    <TargetFramework>net11.0</TargetFramework>
+    <AssemblyName>R2rSuffixLibrary.r2r</AssemblyName>
+  </PropertyGroup>
+
+</Project>
diff --git a/src/mono/wasm/testassets/BlazorBasicTestApp/R2rSuffixLibrary/R2rSuffixLibraryMarker.cs b/src/mono/wasm/testassets/BlazorBasicTestApp/R2rSuffixLibrary/R2rSuffixLibraryMarker.cs
new file mode 100644
index 00000000000000..58f414f41e9a88
--- /dev/null
+++ b/src/mono/wasm/testassets/BlazorBasicTestApp/R2rSuffixLibrary/R2rSuffixLibraryMarker.cs
@@ -0,0 +1,7 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+public static class R2rSuffixLibraryMarker
+{
+    public static int Value => 42;
+}
diff --git a/src/native/libs/Common/JavaScript/loader/assets.ts b/src/native/libs/Common/JavaScript/loader/assets.ts
index 839cc6e9768f68..cb02a2074aec02 100644
--- a/src/native/libs/Common/JavaScript/loader/assets.ts
+++ b/src/native/libs/Common/JavaScript/loader/assets.ts
@@ -149,14 +149,6 @@ export async function fetchIcu(asset: IcuAsset): Promise<void> {
 }
 
 export async function fetchAssembly(asset: AssemblyAsset): Promise<void> {
-    return fetchAssemblyInternal(asset, false);
-}
-
-export async function fetchCoreAssembly(asset: AssemblyAsset): Promise<void> {
-    return fetchAssemblyInternal(asset, true);
-}
-
-async function fetchAssemblyInternal(asset: AssemblyAsset, isCoreAssembly: boolean): Promise<void> {
     const assetInternal = asset as AssetEntryInternal;
     totalAssetsToDownload++;
     dotnetAssert.check(assetInternal.virtualPath, "Assembly asset must have virtualPath");
@@ -168,10 +160,6 @@ async function fetchAssemblyInternal(asset: AssemblyAsset, isCoreAssembly: boole
     }
 
     const isWebcilInWasm = assetInternal.virtualPath?.endsWith(".wasm") ?? false;
-    // The SDK places only System.Private.CoreLib and the composite R2R owner in coreAssembly. Crossgen2 names
-    // the owner <entry>.r2r.wasm and every component stub probes for it by that exact name, so it keeps its
-    // .wasm virtual path and is not a managed assembly (see initializeCoreCLR's TPA).
-    assetInternal.isCompositeImage = isCoreAssembly && assetInternal.virtualPath.endsWith(".r2r.wasm");
     normalizeVirtualPath(assetInternal);
 
     if (isWebcilInWasm) {
@@ -577,6 +565,8 @@ export function verifyAllAssetsDownloaded(): void {
 
 function normalizeVirtualPath(asset: AssetEntryInternal): void {
     dotnetAssert.check(asset.virtualPath, "Asset must have virtualPath");
+    // Component stubs probe for the composite owner by its crossgen2 name (<entry>.r2r.wasm), so it keeps
+    // its .wasm virtual path; it is not a managed assembly (see initializeCoreCLR's TPA).
     if (!asset.isCompositeImage) {
         asset.virtualPath = asset.virtualPath!.replace(/\.wasm$/, ".dll");
     }
diff --git a/src/native/libs/Common/JavaScript/loader/run.ts b/src/native/libs/Common/JavaScript/loader/run.ts
index c2c70435840c44..6604334d3ce51e 100644
--- a/src/native/libs/Common/JavaScript/loader/run.ts
+++ b/src/native/libs/Common/JavaScript/loader/run.ts
@@ -8,7 +8,7 @@ import { exit, runtimeState } from "./exit";
 import { createPromiseCompletionSource } from "./promise-completion-source";
 import { getIcuResourceName } from "./icu";
 import { loaderConfig, validateLoaderConfig } from "./config";
-import { fetchAssembly, fetchCoreAssembly, fetchIcu, fetchNativeSymbols, fetchPdb, fetchSatelliteAssemblies, fetchVfs, fetchMainWasm, loadDotnetModule, loadJSModule, nativeModulePromiseController, verifyAllAssetsDownloaded, callLibraryInitializerOnRuntimeReady, callLibraryInitializerOnRuntimeConfigLoaded, prefetchAllResources, prefetchJSModuleLinks, resolveAllDownloadsQueued } from "./assets";
+import { fetchAssembly, fetchIcu, fetchNativeSymbols, fetchPdb, fetchSatelliteAssemblies, fetchVfs, fetchMainWasm, loadDotnetModule, loadJSModule, nativeModulePromiseController, verifyAllAssetsDownloaded, callLibraryInitializerOnRuntimeReady, callLibraryInitializerOnRuntimeConfigLoaded, prefetchAllResources, prefetchJSModuleLinks, resolveAllDownloadsQueued } from "./assets";
 import { initPolyfillsLoader } from "./polyfills";
 import { validateEngineFeatures } from "./bootstrap";
 
@@ -117,7 +117,7 @@ export async function createRuntime(downloadOnly: boolean, httpCacheOnly: boolea
         const runtimeModulePromise: Promise<JsModuleExports> = loadDotnetModule(resources.jsModuleRuntime[0]);
         const wasmNativePromise: Promise<Response> = fetchMainWasm(resources.wasmNative[0]);
 
-        const coreAssembliesPromise = forEachResource(resources.coreAssembly, fetchCoreAssembly);
+        const coreAssembliesPromise = forEachResource(resources.coreAssembly, fetchAssembly);
 
         const icuResourceName = getIcuResourceName();
         const icuDataPromise = forEachResource(resources.icu, fetchIcu, asset => asset.name === icuResourceName);
diff --git a/src/native/libs/Common/JavaScript/types/public-api.ts b/src/native/libs/Common/JavaScript/types/public-api.ts
index bf15adfa46ee7e..21820addf6496c 100644
--- a/src/native/libs/Common/JavaScript/types/public-api.ts
+++ b/src/native/libs/Common/JavaScript/types/public-api.ts
@@ -269,6 +269,11 @@ export type WebcilAsset = AssemblyAsset & {
      * plain (non-R2R) webcil.
      */
     tableSize?: number;
+    /**
+     * Set on the composite ReadyToRun owner image. It carries native code for its component assemblies
+     * but is not itself a managed assembly: it keeps its .wasm virtual path and is not a trusted platform assembly.
+     */
+    isCompositeImage?: boolean;
 };
 export type PdbAsset = Asset & {
     virtualPath: string;
diff --git a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonBuilderHelper.cs b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonBuilderHelper.cs
index de63f0f7f0383b..554ae0f476f01f 100644
--- a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonBuilderHelper.cs
+++ b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonBuilderHelper.cs
@@ -213,7 +213,7 @@ public int GetDebugLevel(bool hasPdb)
             return intValue;
         }
 
-        public string TransformResourcesToAssets(BootJsonData config, bool bundlerFriendly = false, Dictionary<string, (int tableSize, int payloadSize)>? webcilSizes = null)
+        public string TransformResourcesToAssets(BootJsonData config, bool bundlerFriendly = false, Dictionary<string, (int tableSize, int payloadSize)>? webcilSizes = null, HashSet<string>? compositeImages = null)
         {
             List<string> imports = [];
 
@@ -333,6 +333,9 @@ public string TransformResourcesToAssets(BootJsonData config, bool bundlerFriend
                     }
                 }
 
+                if (subFolder is null && compositeImages?.Contains(a.Key) == true)
+                    asset.isCompositeImage = true;
+
                 if (bundlerFriendly)
                 {
                     string escaped = EscapeName(string.Concat(subFolder, a.Key));
diff --git a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonData.cs b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonData.cs
index dd26c45807d2da..a161042c338bfa 100644
--- a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonData.cs
+++ b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonData.cs
@@ -415,6 +415,14 @@ public class WebcilAsset : GeneralAsset
     /// </summary>
     [DataMember(EmitDefaultValue = false)]
     public int? payloadSize { get; set; }
+
+    /// <summary>
+    /// Set on the composite ReadyToRun owner image. It holds native code for its component assemblies
+    /// but is not itself a managed assembly: the loader keeps its <c>.wasm</c> virtual path (component
+    /// stubs probe for it by that name) and excludes it from the trusted platform assemblies.
+    /// </summary>
+    [DataMember(EmitDefaultValue = false)]
+    public bool? isCompositeImage { get; set; }
 }
 
 [DataContract]
diff --git a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs
index 41e864feb49d5c..56104bbc936f3c 100644
--- a/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs
+++ b/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs
@@ -130,6 +130,8 @@ private void WriteBootConfig(string entryAssemblyName)
         // boot config, letting the loader stream-instantiate instead of buffering and parsing. The
         // AttachWebcilSizes task attaches these as PayloadSize/TableSize metadata on the resources.
         var webcilSizes = new Dictionary<string, (int tableSize, int payloadSize)>();
+        // Routes of composite ReadyToRun owner images, flagged isCompositeImage in the boot config.
+        var compositeImages = new HashSet<string>(StringComparer.Ordinal);
 
         var result = new BootJsonData
         {
@@ -293,10 +295,11 @@ private void WriteBootConfig(string entryAssemblyName)
                     }
                 }
                 else if (string.Equals("WasmResource", assetTraitName, StringComparison.OrdinalIgnoreCase)
-                    && string.Equals("core", assetTraitValue, StringComparison.OrdinalIgnoreCase))
+                    && string.Equals("readyToRunComposite", assetTraitValue, StringComparison.OrdinalIgnoreCase))
                 {
                     MapFingerprintedAsset(resourceData, resourceRoute, resourceName);
-                    Log.LogMessage(MessageImportance.Low, "Candidate '{0}' is defined as a core assembly.", resource.ItemSpec);
+                    Log.LogMessage(MessageImportance.Low, "Candidate '{0}' is defined as a composite ReadyToRun image.", resource.ItemSpec);
+                    compositeImages.Add(resourceRoute);
                     resourceList = resourceData.coreAssembly;
                 }
                 else if (string.Equals("runtime", assetTraitValue, StringComparison.OrdinalIgnoreCase))
@@ -522,7 +525,7 @@ private void WriteBootConfig(string entryAssemblyName)
 
         string? imports = null;
         if (IsTargeting100OrLater())
-            imports = helper.TransformResourcesToAssets(result, BundlerFriendly, webcilSizes);
+            imports = helper.TransformResourcesToAssets(result, BundlerFriendly, webcilSizes, compositeImages);
 
         helper.WriteConfigToFile(result, OutputPath, mergeWith: MergeWith, imports: imports);
 

From 15a61fdf4210c2c98c48790fb20a3f88af9b06db Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Fri, 25 Sep 2026 12:57:10 -0500
Subject: [PATCH 05/11] Drop WebCIL code-section WASM_MEMORY_ADDR_REL_SLEB
 handling

The relocation only arises with dotnet/runtime#134555, where a same-image
managed helper is returned as IAT_VALUE but genEmitHelperCall still loads the
PEP through an indirection cell. Encoding it as a function index would load
from imageBase + funcIndex, so the fix belongs in the JIT. On main no code
path emits it for composite images.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../Common/Compiler/ObjectWriter/WebCilObjectWriter.cs     | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/src/coreclr/tools/Common/Compiler/ObjectWriter/WebCilObjectWriter.cs b/src/coreclr/tools/Common/Compiler/ObjectWriter/WebCilObjectWriter.cs
index d9f74730988802..d61c5757135988 100644
--- a/src/coreclr/tools/Common/Compiler/ObjectWriter/WebCilObjectWriter.cs
+++ b/src/coreclr/tools/Common/Compiler/ObjectWriter/WebCilObjectWriter.cs
@@ -853,9 +853,6 @@ private unsafe int ResolveReloc(int sectionIndex, MemoryStream sourceStream, lon
                     case RelocType.WASM_TABLE_INDEX_SLEB:
                     case RelocType.WASM_TABLE_INDEX_REL_I32:
                     case RelocType.WASM_FUNCTION_INDEX_LEB:
-                    // A code-section address names a function index, not an offset into the WebCIL payload.
-                    case RelocType.WASM_MEMORY_ADDR_REL_SLEB when
-                        _sections[definedSymbol.SectionIndex] is WasmSection { Type: WasmSectionType.Code }:
                     {
                         // These relocations reference a wasm structural index (function, type,
                         // table entry, or well-known global). For R2R we self-resolve them here to
@@ -864,10 +861,6 @@ private unsafe int ResolveReloc(int sectionIndex, MemoryStream sourceStream, lon
                         {
                             throw new InvalidOperationException($"Symbol '{reloc.SymbolName}' was not registered. Relocation type {reloc.Type}.");
                         }
-                        if (reloc.Type == RelocType.WASM_MEMORY_ADDR_REL_SLEB && symbol.IndexSpace != WasmIndexSpace.Function)
-                        {
-                            throw new InvalidDataException($"Code-section relocation for '{reloc.SymbolName}' does not reference a function.");
-                        }
 
                         if (shrink && Relocation.IsVariableLength(reloc.Type))
                         {

From 51909e99b5b039bbcd7e661e4951b9da4cfd8453 Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Fri, 25 Sep 2026 15:16:05 -0500
Subject: [PATCH 06/11] Drop composite ban re-added by the main merge

#132721 duplicated the composite and container-format errors into
_WasmCoreClrSelectR2RDirectories. That brought back the composite
rejection this PR removes and failed PublishRunAllPagesComposite on CI.
Keep the checks in _WasmCoreClrValidateReadyToRun, which runs first, and
move the new WasmPerformanceInstrumentation check there.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 ...crosoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

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
index 534d3aac2b7909..ef14fb88830085 100644
--- 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
@@ -36,13 +36,6 @@ Copyright (c) .NET Foundation. All rights reserved.
        _ResolveGlobalizationConfiguration. -->
   <Target Name="_WasmCoreClrSelectR2RDirectories"
           DependsOnTargets="_ResolveWasmConfiguration">
-    <Error Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' == 'true'"
-           Text="PublishReadyToRunComposite is not supported for CoreCLR browser-wasm; only non-composite (per-assembly) R2R images are supported." />
-    <Error Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunContainerFormat)' != 'wasm'"
-           Text="PublishReadyToRunContainerFormat '$(PublishReadyToRunContainerFormat)' is not supported for CoreCLR browser-wasm; only 'wasm' is supported." />
-    <!-- CPU sampling observes only interpreted frames, so R2R (native wasm) methods are missing from traces until #130521. -->
-    <Error Condition="'$(PublishReadyToRun)' == 'true' and '$(WasmPerformanceInstrumentation)' != ''"
-           Text="WasmPerformanceInstrumentation is not supported together with PublishReadyToRun on CoreCLR browser-wasm. See https://github.com/dotnet/runtime/issues/130521." />
     <PropertyGroup>
       <_WasmRuntimePackR2RDir Condition="'$(_WasmRuntimePackR2RDir)' == '' and '$(_RuntimePackNativeDir)' != ''">$([MSBuild]::NormalizeDirectory('$(_RuntimePackNativeDir)', 'r2r'))</_WasmRuntimePackR2RDir>
       <!-- Computed unconditionally: the trimmed-closure restriction below needs it with ReadyToRun off too. -->
@@ -68,6 +61,9 @@ Copyright (c) .NET Foundation. All rights reserved.
            Text="PublishReadyToRunComposite for CoreCLR browser-wasm requires WebCIL-in-Wasm assemblies; enable WasmEnableWebcil." />
     <Error Condition="'$(PublishReadyToRunContainerFormat)' != 'wasm'"
            Text="PublishReadyToRunContainerFormat '$(PublishReadyToRunContainerFormat)' is not supported for CoreCLR browser-wasm; only 'wasm' is supported." />
+    <!-- CPU sampling observes only interpreted frames, so R2R (native wasm) methods are missing from traces until #130521. -->
+    <Error Condition="'$(WasmPerformanceInstrumentation)' != ''"
+           Text="WasmPerformanceInstrumentation is not supported together with PublishReadyToRun on CoreCLR browser-wasm. See https://github.com/dotnet/runtime/issues/130521." />
     <Error Condition="('$(_IsPublishing)' == 'true' or '$(WasmBuildingForNestedPublish)' == 'true' or '$(WasmBuildOnlyAfterPublish)' == 'true') and ('$(Crossgen2InBuildDir)' == '' or !Exists('$(Crossgen2InBuildDir)')) and '@(ResolvedCrossgen2Pack)' == ''"
            Text="PublishReadyToRun=true for CoreCLR browser-wasm requires a wasm-capable crossgen2, but none was resolved. Set Crossgen2InBuildDir to an in-build crossgen2 directory (or provide a ResolvedCrossgen2Pack) until wasm crossgen2 support flows through the base SDK (dotnet/sdk#55785)." />
   </Target>

From 3ffb97466460795b140948543e2dc976a414c05e Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Fri, 25 Sep 2026 15:36:22 -0500
Subject: [PATCH 07/11] Point container-format comment at the validating target

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../build/Microsoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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
index ef14fb88830085..6e5fa73e6cf852 100644
--- 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
@@ -19,7 +19,7 @@ Copyright (c) .NET Foundation. All rights reserved.
 
   <PropertyGroup Condition="'$(PublishReadyToRun)' == 'true'">
     <!-- Override only the incompatible SDK default: net11+ defaults ContainerFormat=pe (unloadable on wasm).
-         An explicit unsupported value is left as-is and rejected by _WasmCoreClrSelectR2RDirectories. -->
+         An explicit unsupported value is left as-is and rejected by _WasmCoreClrValidateReadyToRun. -->
     <PublishReadyToRunContainerFormat Condition="'$(PublishReadyToRunContainerFormat)' == '' or '$(PublishReadyToRunContainerFormat)' == 'pe'">wasm</PublishReadyToRunContainerFormat>
     <!-- Keep the existing per-assembly behavior unless composite is explicitly requested. -->
     <PublishReadyToRunComposite Condition="'$(PublishReadyToRunComposite)' == ''">false</PublishReadyToRunComposite>

From 43c27ac13109050cfa1d4c6b3f6e99bc44bcd0ba Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Fri, 25 Sep 2026 20:19:42 -0500
Subject: [PATCH 08/11] [wasm][coreclr] Strip R2R debug info by default for
 browser-wasm publish (#134689)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

## Summary

Pass `--strip-debug-info` to crossgen2 for CoreCLR browser-wasm
ReadyToRun publish. This drops the R2R `DebugInfo` section (native-to-IL
offset maps and variable locations) from shipped images. Opt out with
`PublishReadyToRunStripDebugInfo=false` to keep the data for debugging
R2R code (e.g. the cDAC work in #133086 / #133890).

Also makes crossgen2 argument changes invalidate per-app R2R images.
`_CreateR2RImages` only tracks file inputs, so toggling
`PublishReadyToRunStripDebugInfo` (or any
`PublishReadyToRunCrossgen2ExtraArgs` change) previously left stale
images in `obj/R2R`. The arguments are now written to
`obj/wasm-r2r-args.stamp` (only when different) and added to
`_ReadyToRunCompilerInputs`, mirroring the existing P/Invoke manifest
input.

> [!IMPORTANT]
> Stacked on #134618, which rewrites the same targets file. Retarget to
`main` after it merges.

## Size impact

Per-assembly R2R images compiled directly with crossgen2 using the SDK's
browser-wasm arguments (`--obj-format:wasm --opt-cross-module:*
--codegenopt:JitWasm*NyiToR2RUnsupported=1`), with and without
`--strip-debug-info`. Total for System.Private.CoreLib,
System.Text.Json, System.Linq, and System.Collections:

| Compiler | Raw saved | gzip -9 saved | brotli -q 11 saved |
| --- | --- | --- | --- |
| Current (#134618 base) | 859,712 B (2.4%) | 624,690 B (7.1%) | 565,366
B (9.4%) |
| With #133086 variable info | 2,105,520 B (5.6%) | 1,332,733 B (13.9%)
| 1,121,574 B (17.0%) |

<details>
<summary>Per-assembly brotli sizes (bytes, keep → strip)</summary>

| Assembly | Current | With #133086 |
| --- | --- | --- |
| System.Private.CoreLib | 4,822,231 → 4,347,541 | 5,331,799 → 4,403,849
|
| System.Text.Json | 823,314 → 761,533 | 887,982 → 754,444 |
| System.Linq | 219,177 → 200,471 | 238,853 → 200,441 |
| System.Collections | 119,635 → 109,446 | 130,742 → 109,068 |

The #133086 compiler is based on an older commit, so compare keep vs.
strip within a column rather than across columns.
</details>

## Validation

- MSBuild evaluation: `--strip-debug-info` is present by default, absent
with `PublishReadyToRunStripDebugInfo=false`, and absent when
`PublishReadyToRun` is off.
- Incremental harness: `_CreateR2RImages` runs on first build, skips
when unchanged, reruns on opt-out, skips when repeated, and reruns when
switching back.
- Not yet run: an end-to-end browser-wasm publish loading stripped
images in a browser (Wasm.Build.Tests in CI will cover this).

Runtime-pack framework R2R images (used only by the dev-loop build) are
unchanged; publish recompiles the whole closure through these targets.
`--strip-inlining-info` is intentionally not included: it removes
`CrossModuleInlineInfo`, and cross-module inlining is load-bearing on
wasm, so it needs separate validation.

> [!NOTE]
> This pull request was created with assistance from GitHub Copilot.

---------

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 ...t.NET.Sdk.WebAssembly.Browser.CoreCLR.targets | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

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
index 6e5fa73e6cf852..97fef920278c75 100644
--- 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
@@ -27,6 +27,9 @@ Copyright (c) .NET Foundation. All rights reserved.
     <PublishReadyToRunCrossgen2ExtraArgs>$(PublishReadyToRunCrossgen2ExtraArgs);--opt-cross-module:*</PublishReadyToRunCrossgen2ExtraArgs>
     <!-- NYI/SIMD methods crossgen2 can't emit into R2R fall back to the runtime JIT. -->
     <PublishReadyToRunCrossgen2ExtraArgs>$(PublishReadyToRunCrossgen2ExtraArgs);--codegenopt:JitWasmNyiToR2RUnsupported=1;--codegenopt:JitWasmSimdNyiToR2RUnsupported=1</PublishReadyToRunCrossgen2ExtraArgs>
+    <!-- Strip R2R debug info (IL offset maps and variable locations) to minimize download size.
+         Set PublishReadyToRunStripDebugInfo=false to keep it for debugging R2R code. -->
+    <PublishReadyToRunCrossgen2ExtraArgs Condition="'$(PublishReadyToRunStripDebugInfo)' != 'false'">$(PublishReadyToRunCrossgen2ExtraArgs);--strip-debug-info</PublishReadyToRunCrossgen2ExtraArgs>
   </PropertyGroup>
 
   <!-- Prebuilt R2R probe directory for ConvertDllsToWebcil. PublishTrimmed is deliberately not consulted:
@@ -237,6 +240,19 @@ Copyright (c) .NET Foundation. All rights reserved.
       <_ReadyToRunCompilerInputs Include="$(_WasmResolvedCrossgen2Dir)crossgen2*;$(_WasmResolvedCrossgen2Dir)clrjit_universal_wasm_*"
                                  Condition="'$(_WasmResolvedCrossgen2Dir)' != ''" />
     </ItemGroup>
+    <!-- Crossgen2 arguments (e.g. toggling PublishReadyToRunStripDebugInfo) don't change any file input, so
+         stamp them; WriteOnlyWhenDifferent bumps the timestamp only when the arguments change. -->
+    <PropertyGroup>
+      <_WasmReadyToRunArgsStamp>$(IntermediateOutputPath)wasm-r2r-args.stamp</_WasmReadyToRunArgsStamp>
+    </PropertyGroup>
+    <WriteLinesToFile File="$(_WasmReadyToRunArgsStamp)"
+                      Lines="$(PublishReadyToRunCrossgen2ExtraArgs)"
+                      Overwrite="true"
+                      WriteOnlyWhenDifferent="true" />
+    <ItemGroup>
+      <_ReadyToRunCompilerInputs Include="$(_WasmReadyToRunArgsStamp)" />
+      <FileWrites Include="$(_WasmReadyToRunArgsStamp)" />
+    </ItemGroup>
   </Target>
 
   <!-- Delete per-app images and composite component stubs left in obj/R2R by a previous build or

From e6a4e52407df7f47871da7630ca5c848305e9966 Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Fri, 25 Sep 2026 23:07:28 -0500
Subject: [PATCH 09/11] Drop the browser R2R --strip-debug-info default

#134690 adds --strip-debug-info and --strip-inlining-info for browser and
wasi ReadyToRun where the other strip defaults live, so the wasm pack
shouldn't add its own.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../Microsoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets      | 3 ---
 1 file changed, 3 deletions(-)

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
index 97fef920278c75..dfe96fb0f597b7 100644
--- 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
@@ -27,9 +27,6 @@ Copyright (c) .NET Foundation. All rights reserved.
     <PublishReadyToRunCrossgen2ExtraArgs>$(PublishReadyToRunCrossgen2ExtraArgs);--opt-cross-module:*</PublishReadyToRunCrossgen2ExtraArgs>
     <!-- NYI/SIMD methods crossgen2 can't emit into R2R fall back to the runtime JIT. -->
     <PublishReadyToRunCrossgen2ExtraArgs>$(PublishReadyToRunCrossgen2ExtraArgs);--codegenopt:JitWasmNyiToR2RUnsupported=1;--codegenopt:JitWasmSimdNyiToR2RUnsupported=1</PublishReadyToRunCrossgen2ExtraArgs>
-    <!-- Strip R2R debug info (IL offset maps and variable locations) to minimize download size.
-         Set PublishReadyToRunStripDebugInfo=false to keep it for debugging R2R code. -->
-    <PublishReadyToRunCrossgen2ExtraArgs Condition="'$(PublishReadyToRunStripDebugInfo)' != 'false'">$(PublishReadyToRunCrossgen2ExtraArgs);--strip-debug-info</PublishReadyToRunCrossgen2ExtraArgs>
   </PropertyGroup>
 
   <!-- Prebuilt R2R probe directory for ConvertDllsToWebcil. PublishTrimmed is deliberately not consulted:

From 8adbeb86da25cbb80c56b0beea6810c4ba9b9777 Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Fri, 25 Sep 2026 23:07:28 -0500
Subject: [PATCH 10/11] Recompile per-app R2R images when switching composite
 mode

Composite component stubs are written as <name>.wasm, the same names as
per-assembly images. After a composite publish, a per-assembly republish
(-p:PublishReadyToRunComposite=false) found them up to date, pruned the
composite owner, and shipped stubs that fail startup. Add the mode to the
crossgen2 configuration stamp, and switch modes in the trimmed composite
test.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 ...NET.Sdk.WebAssembly.Browser.CoreCLR.targets |  8 +++++---
 .../wasm/Wasm.Build.Tests/ReadyToRunTests.cs   | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+), 3 deletions(-)

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
index dfe96fb0f597b7..898b199401cea3 100644
--- 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
@@ -237,13 +237,15 @@ Copyright (c) .NET Foundation. All rights reserved.
       <_ReadyToRunCompilerInputs Include="$(_WasmResolvedCrossgen2Dir)crossgen2*;$(_WasmResolvedCrossgen2Dir)clrjit_universal_wasm_*"
                                  Condition="'$(_WasmResolvedCrossgen2Dir)' != ''" />
     </ItemGroup>
-    <!-- Crossgen2 arguments (e.g. toggling PublishReadyToRunStripDebugInfo) don't change any file input, so
-         stamp them; WriteOnlyWhenDifferent bumps the timestamp only when the arguments change. -->
+    <!-- Crossgen2 configuration that isn't a file input: extra arguments (e.g. -p:PublishReadyToRunStripDebugInfo)
+         and the composite mode, whose component stubs share the per-assembly <name>.wasm output names and would
+         otherwise look up-to-date after a composite publish. WriteOnlyWhenDifferent bumps the timestamp only
+         when this configuration changes. -->
     <PropertyGroup>
       <_WasmReadyToRunArgsStamp>$(IntermediateOutputPath)wasm-r2r-args.stamp</_WasmReadyToRunArgsStamp>
     </PropertyGroup>
     <WriteLinesToFile File="$(_WasmReadyToRunArgsStamp)"
-                      Lines="$(PublishReadyToRunCrossgen2ExtraArgs)"
+                      Lines="PublishReadyToRunComposite=$(PublishReadyToRunComposite);$(PublishReadyToRunCrossgen2ExtraArgs)"
                       Overwrite="true"
                       WriteOnlyWhenDifferent="true" />
     <ItemGroup>
diff --git a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
index 2980d817eb409f..c7185f6dd7175a 100644
--- a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
@@ -116,6 +116,8 @@ private async Task PublishRunAllPagesCore(Configuration config, bool trimmed, bo
                 if (composite)
                     AssertCompositeReadyToRun(frameworkDir);
                 AssertNoDuplicateAssemblies(frameworkDir);
+                if (composite)
+                    AssertSwitchingCompositeModeRecompiles(info, config, extraArgs, frameworkDir);
             }
 
             bool suffixLibraryLoaded = false;
@@ -309,6 +311,22 @@ private static void AssertCoreLibReadyToRun(string frameworkDir, bool expectRead
                 Assert.Equal(0, tableSize);
         }
 
+        // Component stubs share the per-assembly <name>.wasm output names, so a mode switch must recompile them
+        // instead of treating them as up-to-date per-assembly images that probe for a pruned composite owner.
+        // Switch back afterwards so the caller still runs the composite app.
+        private void AssertSwitchingCompositeModeRecompiles(ProjectInfo info, Configuration config, string extraArgs, string frameworkDir)
+        {
+            string coreLibImage = Path.Combine(GetObjSubDir(config, "R2R"), "System.Private.CoreLib.wasm");
+            System.DateTime compositeStubTime = File.GetLastWriteTimeUtc(coreLibImage);
+
+            BlazorPublish(info, config, new PublishOptions(UseCache: false, ExtraMSBuildArgs: $"{extraArgs} -p:PublishReadyToRunComposite=false"));
+            Assert.True(File.GetLastWriteTimeUtc(coreLibImage) > compositeStubTime,
+                $"'{coreLibImage}' was not recompiled after switching from composite to per-assembly ReadyToRun.");
+
+            BlazorPublish(info, config, new PublishOptions(UseCache: false, ExtraMSBuildArgs: extraArgs));
+            AssertCompositeReadyToRun(frameworkDir);
+        }
+
         // The boot config flags exactly the composite owner, delivered via coreAssembly under its crossgen2 name so
         // component stubs can probe for it; an assembly merely named *.r2r stays an ordinary, unflagged assembly.
         private void AssertCompositeReadyToRun(string frameworkDir)

From a36ea807434fa5d52148e119fdc7ba446453535c Mon Sep 17 00:00:00 2001
From: Larry Ewing <lewing@microsoft.com>
Date: Thu, 1 Oct 2026 09:33:28 -0500
Subject: [PATCH 11/11] Address composite R2R review: track the shim, keep
 GetBootConfigPath unchanged

Mark the Crossgen2Tasks shim wiring (Helix payload, composite task
validation, test args) with TODO-WASM pointing at #135023.

Revert the newest-file selection in ProjectProviderBase.GetBootConfigPath.
Only the composite mode-switch republish leaves another mode's fingerprinted
dotnet.js behind, so clear the published _framework there instead. The mode
switch only needs obj to be incremental.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 src/libraries/sendtohelix-browser.targets              |  1 +
 ...crosoft.NET.Sdk.WebAssembly.Browser.CoreCLR.targets |  3 ++-
 src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs  | 10 +++-------
 src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs      |  6 +++++-
 4 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/src/libraries/sendtohelix-browser.targets b/src/libraries/sendtohelix-browser.targets
index 224027c11aee34..26d278bf6f6c3b 100644
--- a/src/libraries/sendtohelix-browser.targets
+++ b/src/libraries/sendtohelix-browser.targets
@@ -297,6 +297,7 @@
          whenever it is built - it is gated on its own path, not on the crossgen2 bin dir, which the WBT test leg
          does not carry. Wasm.Build.Tests (BuildWasmApps) need it for PublishReadyToRunComposite, whose output
          naming the base SDK's ReadyToRun tasks don't implement yet. -->
+    <!-- TODO-WASM https://github.com/dotnet/runtime/issues/135023: drop the BuildWasmApps clause once the SDK names wasm R2R outputs. -->
     <ItemGroup Condition="('$(NeedsEMSDK)' == 'true' or '$(Scenario)' == 'BuildWasmApps') and '$(RuntimeFlavor)' == 'CoreCLR' and Exists('$(ArtifactsBinDir)Crossgen2Tasks\$(TasksConfiguration)\')">
       <HelixCorrelationPayload Include="$(ArtifactsBinDir)Crossgen2Tasks\$(TasksConfiguration)\"
                                Destination="Crossgen2Tasks/$(Configuration)" />
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
index 898b199401cea3..1a353881064452 100644
--- 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
@@ -70,7 +70,8 @@ Copyright (c) .NET Foundation. All rights reserved.
 
   <!-- Composite needs wasm-aware ReadyToRun tasks: the component stubs probe for the owner as <entry>.r2r.wasm,
        and crossgen2 writes each component stub as <name>.wasm. Tasks without wasm naming plan <entry>.r2r.dll
-       and <name>.dll outputs that are never produced, so fail before the (long) composite compile. -->
+       and <name>.dll outputs that are never produced, so fail before the (long) composite compile.
+       TODO-WASM https://github.com/dotnet/runtime/issues/135023: revisit once the SDK names wasm R2R outputs. -->
   <Target Name="_WasmCoreClrValidateCompositeTasks"
           Condition="'$(PublishReadyToRun)' == 'true' and '$(PublishReadyToRunComposite)' == 'true'"
           BeforeTargets="_CreateR2RImages">
diff --git a/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs b/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs
index ba9e8f3e8bd39b..ccd4b435dc5253 100644
--- a/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs
@@ -560,11 +560,9 @@ public string GetBootConfigPath(string binFrameworkDir, string? bootConfigFileNa
         {
             string bootFileNameWithoutExtension = Path.GetFileNameWithoutExtension(bootConfigFileName);
             string bootFileExtension = Path.GetExtension(bootConfigFileName);
-            // A republish into an existing output leaves the previous fingerprinted copy beside the current one;
-            // pick the newest, as FindAndAssertDotnetFiles does, so assertions read the active boot config.
             string? fingerprintedBootJsonPath = Directory
                 .EnumerateFiles(binFrameworkDir)
-                .Where(f =>
+                .FirstOrDefault(f =>
                 {
                     if (Path.GetExtension(f) != bootFileExtension)
                         return false;
@@ -577,10 +575,8 @@ public string GetBootConfigPath(string binFrameworkDir, string? bootConfigFileNa
                         return false;
 
                     return true;
-                })
-                .OrderByDescending(File.GetLastWriteTimeUtc)
-                .FirstOrDefault();
-
+                });
+            
             if (fingerprintedBootJsonPath == null)
                 throw new XunitException($"Could not find boot config '{bootConfigFileName}' with fingerprint in '{binFrameworkDir}'");
 
diff --git a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
index c7185f6dd7175a..84f705655670cd 100644
--- a/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/ReadyToRunTests.cs
@@ -270,6 +270,7 @@ private void AssertPerAppCrossgenRan(Configuration config, bool expected)
         // that path stays covered. Each is passed only when present under BASE_DIR: the no-workload leg resolves
         // crossgen2 itself from the SDK pack (the SDK restores it when PublishReadyToRun is set), so passing a
         // non-existent Crossgen2InBuildDir there would break the call-helpers generator. All inert if BASE_DIR is unset.
+        // TODO-WASM https://github.com/dotnet/runtime/issues/135023: drop the composite-only shim once the SDK names wasm R2R outputs.
         private static string GetR2RBuildArgs(Configuration config, bool composite)
         {
             string? baseDir = EnvironmentVariables.BaseDir;
@@ -313,16 +314,19 @@ private static void AssertCoreLibReadyToRun(string frameworkDir, bool expectRead
 
         // Component stubs share the per-assembly <name>.wasm output names, so a mode switch must recompile them
         // instead of treating them as up-to-date per-assembly images that probe for a pruned composite owner.
-        // Switch back afterwards so the caller still runs the composite app.
+        // Switch back afterwards so the caller still runs the composite app. Only obj is incremental here: clear the
+        // published _framework so each mode's fingerprinted assets don't accumulate beside the other's.
         private void AssertSwitchingCompositeModeRecompiles(ProjectInfo info, Configuration config, string extraArgs, string frameworkDir)
         {
             string coreLibImage = Path.Combine(GetObjSubDir(config, "R2R"), "System.Private.CoreLib.wasm");
             System.DateTime compositeStubTime = File.GetLastWriteTimeUtc(coreLibImage);
 
+            Directory.Delete(frameworkDir, recursive: true);
             BlazorPublish(info, config, new PublishOptions(UseCache: false, ExtraMSBuildArgs: $"{extraArgs} -p:PublishReadyToRunComposite=false"));
             Assert.True(File.GetLastWriteTimeUtc(coreLibImage) > compositeStubTime,
                 $"'{coreLibImage}' was not recompiled after switching from composite to per-assembly ReadyToRun.");
 
+            Directory.Delete(frameworkDir, recursive: true);
             BlazorPublish(info, config, new PublishOptions(UseCache: false, ExtraMSBuildArgs: extraArgs));
             AssertCompositeReadyToRun(frameworkDir);
         }