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/libraries/sendtohelix-browser.targets b/src/libraries/sendtohelix-browser.targets
index 4762716bdfc717..26d278bf6f6c3b 100644
--- a/src/libraries/sendtohelix-browser.targets
+++ b/src/libraries/sendtohelix-browser.targets
@@ -295,8 +295,10 @@
          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('$(ArtifactsBinDir)Crossgen2Tasks\$(TasksConfiguration)\')">
+         does not carry. Wasm.Build.Tests (BuildWasmApps) need it for PublishReadyToRunComposite, whose output
+         naming the base SDK's ReadyToRun tasks don't implement yet. -->
+    <!-- TODO-WASM https://github.com/dotnet/runtime/issues/135023: drop the BuildWasmApps clause once the SDK names wasm R2R outputs. -->
+    <ItemGroup Condition="('$(NeedsEMSDK)' == 'true' or '$(Scenario)' == 'BuildWasmApps') and '$(RuntimeFlavor)' == 'CoreCLR' and Exists('$(ArtifactsBinDir)Crossgen2Tasks\$(TasksConfiguration)\')">
       <HelixCorrelationPayload Include="$(ArtifactsBinDir)Crossgen2Tasks\$(TasksConfiguration)\"
                                Destination="Crossgen2Tasks/$(Configuration)" />
     </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 50ca9b4e273791..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
@@ -19,9 +19,9 @@ 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 '$(PublishReadyToRunContainerFormat)' == 'pe'">wasm</PublishReadyToRunContainerFormat>
-    <!-- Default non-composite when unset; an explicit composite request is rejected below. -->
+    <!-- Keep the existing per-assembly behavior unless composite is explicitly requested. -->
     <PublishReadyToRunComposite Condition="'$(PublishReadyToRunComposite)' == ''">false</PublishReadyToRunComposite>
     <!-- Compile every assembly into one shared (large) version bubble. -->
     <PublishReadyToRunCrossgen2ExtraArgs>$(PublishReadyToRunCrossgen2ExtraArgs);--opt-cross-module:*</PublishReadyToRunCrossgen2ExtraArgs>
@@ -36,13 +36,6 @@ Copyright (c) .NET Foundation. All rights reserved.
        _ResolveGlobalizationConfiguration. -->
   <Target Name="_WasmCoreClrSelectR2RDirectories"
           DependsOnTargets="_ResolveWasmConfiguration">
-    <Error Condition="'$(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. -->
@@ -58,24 +51,42 @@ 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." />
+    <!-- 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>
 
+  <!-- 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.
+       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">
+    <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>
     <_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
@@ -157,14 +168,26 @@ 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>
@@ -174,7 +197,7 @@ 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 '$(IntermediateLinkDir)' != ''"
           BeforeTargets="_PrepareForReadyToRunCompilation">
     <ItemGroup>
       <!-- Clear the stale base-SDK R2R mark on the untrimmed runtime-pack copy (e.g. CoreLib under native/)
@@ -199,38 +222,55 @@ Copyright (c) .NET Foundation. All rights reserved.
   <!-- Force crossgen (CreateReadyToRunImages) before ProcessPublishFilesForWasm: the latter runs
        AfterTargets=ILLink, which a Blazor publish schedules ahead of R2R, so the images would ship too late. -->
   <Target Name="_WasmEnsureReadyToRunBeforePublish"
-          Condition="'$(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>
+    <!-- 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="PublishReadyToRunComposite=$(PublishReadyToRunComposite);$(PublishReadyToRunCrossgen2ExtraArgs)"
+                      Overwrite="true"
+                      WriteOnlyWhenDifferent="true" />
+    <ItemGroup>
+      <_ReadyToRunCompilerInputs Include="$(_WasmReadyToRunArgsStamp)" />
+      <FileWrites Include="$(_WasmReadyToRunArgsStamp)" />
+    </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('$(_WasmPublishR2RDir)')">
+      <!-- Keep what crossgen2 actually emitted, not the task's publish plan: every compiled image, plus in
+           composite mode a <name>.wasm component stub beside the owner for each composite input. -->
+      <_WasmEmittedPerAppR2R Include="@(_ReadyToRunCompileList->'%(OutputR2RImage)')" />
+      <_WasmEmittedPerAppR2R Include="@(_ReadyToRunCompositeBuildInput->'$(_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="@(_ReadyToRunCompileList->'%(OutputR2RImage)')" />
+                           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 529106d2dc6a94..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
@@ -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 +1058,37 @@ 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 '$(PublishReadyToRunComposite)' == 'true'">
+      <_WasmCompositeCompilation Include="@(_ReadyToRunCompileList)"
+                                 Condition="'%(CreateCompositeImage)' == 'true'" />
+      <_WasmCompositePublishCandidate Include="@(_WasmCompositeCompilation->'%(OutputR2RImage)')" KeepMetadata="OutputR2RImage" />
+      <_WasmCompositePublishCandidate Update="@(_WasmCompositePublishCandidate)"
+                                      ContentRoot="%(RootDir)%(Directory)"
+                                      RelativePath="_framework/%(FileName)%(Extension)" />
+      <_WasmCompositeFingerprintPattern Include="WasmFiles" Pattern="*.wasm" Expression="#[.{fingerprint}]!" />
+    </ItemGroup>
+    <Error Condition="'$(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'" />
     </ItemGroup>
@@ -1065,6 +1107,7 @@ 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)" />
@@ -1111,7 +1154,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     </DefineStaticWebAssets>
 
     <DefineStaticWebAssetEndpoints
-      CandidateAssets="@(_NewWebcilPublishStaticWebAssets)"
+      CandidateAssets="@(_NewWebcilPublishStaticWebAssets);@(_WasmCompositePublishStaticWebAsset)"
       ExistingEndpoints="@(StaticWebAssetEndpoint)"
       ContentTypeMappings="@(StaticWebAssetContentTypeMapping)"
     >
@@ -1120,7 +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 -->
@@ -1273,7 +1316,7 @@ 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..84f705655670cd 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)
@@ -63,16 +72,22 @@ 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" />"""
+                : string.Empty;
             ProjectInfo info = CopyTestAsset(config, aot: false, TestAsset.BlazorBasicTestApp, label,
-                extraProperties: $"<PublishReadyToRun>true</PublishReadyToRun><PublishTrimmed>{(trimmed ? "true" : "false")}</PublishTrimmed>");
-            string extraArgs = GetR2RBuildArgs(config);
+                extraProperties: $"<PublishReadyToRun>true</PublishReadyToRun><PublishReadyToRunComposite>{(composite ? "true" : "false")}</PublishReadyToRunComposite><PublishTrimmed>{(trimmed ? "true" : "false")}</PublishTrimmed>",
+                extraItems: extraItems);
+            if (composite)
+                LogR2RSuffixLibraryMarker();
+            string extraArgs = GetR2RBuildArgs(config, composite);
             if (nativeRelink)
             {
                 // CoreCLR relinks dotnet.native.wasm via the in-tree targets + EMSDK_PATH, not the browser
@@ -86,15 +101,32 @@ 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);
+                if (composite)
+                    AssertSwitchingCompositeModeRecompiles(info, config, extraArgs, 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))]
@@ -110,6 +142,19 @@ 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, composite: true)));
+
+            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)
@@ -219,12 +264,14 @@ 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.
+        // 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;
             if (string.IsNullOrEmpty(baseDir))
@@ -239,26 +286,79 @@ 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);
         }
 
+        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);
         }
+
+        // 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. 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,
+                $"'{coreLibImage}' was not recompiled after switching from composite to per-assembly ReadyToRun.");
+
+            Directory.Delete(frameworkDir, recursive: true);
+            BlazorPublish(info, config, new PublishOptions(UseCache: false, ExtraMSBuildArgs: extraArgs));
+            AssertCompositeReadyToRun(frameworkDir);
+        }
+
+        // The boot config flags exactly the composite owner, delivered via coreAssembly under its crossgen2 name so
+        // component stubs can probe for it; an assembly merely named *.r2r stays an ordinary, unflagged assembly.
+        private void AssertCompositeReadyToRun(string frameworkDir)
+        {
+            AssetsData assets = (AssetsData)_provider.GetBootJson(_provider.GetBootConfigPath(frameworkDir)).resources;
+            WebcilAsset composite = Assert.Single(assets.coreAssembly, asset => asset.isCompositeImage == true);
+            Assert.Equal("BlazorBasicTestApp.r2r.wasm", composite.virtualPath);
+            if (EnvironmentVariables.UseFingerprinting)
+                Assert.Matches(@"^BlazorBasicTestApp\.r2r\.[a-z0-9]{10}\.wasm$", 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");
+
+            string compositePath = Path.Combine(frameworkDir, composite.name);
+            Assert.True(GetReadyToRunTableSize(compositePath) > 0, $"Expected compiled methods in '{compositePath}'.");
+            Assert.True(Directory.EnumerateFiles(frameworkDir, "System.Private.CoreLib*.wasm").Any(),
+                $"Expected a component stub for System.Private.CoreLib in '{frameworkDir}'.");
+        }
+
+        private const string SuffixLibraryLoadedMessage = "Loaded R2rSuffixLibrary.r2r: 42";
+
+        // Make the app call into the R2rSuffixLibrary test asset (referenced for composite runs) so the run proves
+        // it loaded as a component assembly rather than being mistaken for the composite owner.
+        private void LogR2RSuffixLibraryMarker()
+            => UpdateFile("Program.cs", new Dictionary<string, string>
+            {
+                { "var builder", "System.Console.WriteLine($\"Loaded {typeof(R2rSuffixLibraryMarker).Assembly.GetName().Name}: {R2rSuffixLibraryMarker.Value}\");\nvar builder" }
+            });
     }
 }
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/host/host.ts b/src/native/libs/Common/JavaScript/host/host.ts
index 26f2b7ad9f0dcc..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";
 
@@ -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 as AssetEntryInternal).isCompositeImage)
+        .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..cb02a2074aec02 100644
--- a/src/native/libs/Common/JavaScript/loader/assets.ts
+++ b/src/native/libs/Common/JavaScript/loader/assets.ts
@@ -565,7 +565,11 @@ export function verifyAllAssetsDownloaded(): void {
 
 function normalizeVirtualPath(asset: AssetEntryInternal): void {
     dotnetAssert.check(asset.virtualPath, "Asset must have virtualPath");
-    asset.virtualPath = asset.virtualPath!.replace(/\.wasm$/, ".dll");
+    // Component stubs probe for the composite owner by its crossgen2 name (<entry>.r2r.wasm), so it keeps
+    // its .wasm virtual path; it is not a managed assembly (see initializeCoreCLR's TPA).
+    if (!asset.isCompositeImage) {
+        asset.virtualPath = asset.virtualPath!.replace(/\.wasm$/, ".dll");
+    }
     asset.virtualPath = asset.virtualPath.startsWith("/")
         ? asset.virtualPath
         : asset.culture
diff --git a/src/native/libs/Common/JavaScript/types/internal.ts b/src/native/libs/Common/JavaScript/types/internal.ts
index cdf67e75aca812..05c58be9531547 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 & {
diff --git a/src/native/libs/Common/JavaScript/types/public-api.ts b/src/native/libs/Common/JavaScript/types/public-api.ts
index 0da1d6021fdd42..ef1ba15b90dec5 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 90e5608d8d7bc7..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
         {
@@ -292,6 +294,14 @@ private void WriteBootConfig(string entryAssemblyName)
                         }
                     }
                 }
+                else if (string.Equals("WasmResource", assetTraitName, StringComparison.OrdinalIgnoreCase)
+                    && string.Equals("readyToRunComposite", assetTraitValue, StringComparison.OrdinalIgnoreCase))
+                {
+                    MapFingerprintedAsset(resourceData, resourceRoute, resourceName);
+                    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))
                 {
                     MapFingerprintedAsset(resourceData, resourceRoute, resourceName);
@@ -515,7 +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);