From 75fcf55d9a1425ac32c61e25dd6166d68b9cce1c Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Fri, 12 Jun 2026 17:28:24 +0200
Subject: [PATCH 01/13] [wasm] Re-enable System.Formats.Nrbf tests on browser
 CoreCLR

The System.Formats.Nrbf.Tests suite was excluded on browser-wasm +
CoreCLR because test discovery crashed with a FileNotFoundException for
System.Runtime.Serialization.Formatters, Version=11.0.0.0.

Root cause: for a self-contained browser-wasm app, @(ReferenceCopyLocalPaths)
contains two copies of System.Runtime.Serialization.Formatters - the shared
framework's non-functional 8.1.0.0 stub (from the runtime pack) and the
functional 11.0.0.0 build the test references app-local. The WebAssembly SDK
task ComputeWasmBuildAssets dedupes webcil bundle candidates by relative path
on a first-wins, version-blind basis, so the 8.1.0.0 stub got bundled into
_framework and shadowed the app-local 11.0.0.0 copy. xunit discovery then
materializes [InlineData(FormatterTypeStyle.X)] attribute blobs, triggering an
Assembly.Load of the 11.0.0.0 build, which is not present - aborting discovery.

Unlike desktop (framework-dependent deployment, or single-file publish whose
bundler consumes the already version-resolved ResolvedFileToPublish set), the
wasm webcil bundle is assembled at build time from candidates that are not
version-conflict-resolved against ProjectReferences.

Fix: add a CoreCLR-wasm target that applies copy-local-wins semantics before
the bundle candidates are gathered - it drops runtime-pack copy-local
assemblies that are shadowed by a same-named app-local copy. Apps without an
app-local copy of a framework assembly are unaffected.

With the fix the bundled Formatters webcil is the functional 11.0.0.0 build,
discovery finds 153 test cases (was 6) and the suite passes; the ReadTests
hierarchy correctly skips on browser since BinaryFormatter is unsupported there.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/libraries/tests.proj                      |  2 --
 .../build/BrowserWasmApp.CoreCLR.targets      | 34 +++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/src/libraries/tests.proj b/src/libraries/tests.proj
index 4de29857494251..3a733a0604e79f 100644
--- a/src/libraries/tests.proj
+++ b/src/libraries/tests.proj
@@ -185,8 +185,6 @@
 
   <!-- https://github.com/dotnet/runtime/issues/125495 - These tests are disabled on browser/CoreCLR because of crashes and test failures. -->
   <ItemGroup Condition="'$(TargetOS)' == 'browser' and '$(RuntimeFlavor)' == 'CoreCLR' and '$(RunDisabledWasmTests)' != 'true'">
-    <!-- test failures -->
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Formats.Nrbf\tests\System.Formats.Nrbf.Tests.csproj" />
     <!-- long running suites -->
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Linq\tests\System.Linq.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Memory\tests\System.Memory.Tests.csproj" />
diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index e94f759abc4f69..b83bf16ec25a33 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -178,6 +178,40 @@
                      '$(WasmBuildingForNestedPublish)' != 'true' and
                      '$(UsingBrowserRuntimeWorkload)' != 'true'" />
 
+  <!-- ======================== Prefer app-local assemblies over runtime-pack copies ========================
+
+    For a self-contained browser-wasm app, @(ReferenceCopyLocalPaths) can contain two copies of the
+    same assembly: the runtime-pack copy (under $(MicrosoftNetCoreAppRuntimePackDir)) and an app-local
+    copy referenced out-of-band at a different version. ComputeWasmBuildAssets dedupes the webcil bundle
+    candidates by relative path (first-wins, version-blind), so the runtime-pack copy can shadow the
+    app-local one in _framework. The canonical case is System.Runtime.Serialization.Formatters: the
+    shared framework ships a non-functional 8.1.0.0 stub while the app references the functional 11.0.0.0
+    build, so an Assembly.Load for 11.0.0.0 then fails with FileNotFoundException.
+
+    Resolve it the way a self-contained app loads assemblies (copy-local wins): drop runtime-pack copies
+    shadowed by a same-named app-local copy before the candidates are gathered. Apps without an app-local
+    copy of a framework assembly are unaffected.
+  -->
+  <Target Name="_CoreCLRPreferAppLocalAssembliesOverRuntimePack"
+          BeforeTargets="_ComputeWasmBuildCandidates;_GatherWasmFilesToBuild"
+          Condition="'$(IsBrowserWasmProject)' == 'true' and '$(MicrosoftNetCoreAppRuntimePackDir)' != ''">
+    <ItemGroup>
+      <!-- App-local (non-runtime-pack) managed assemblies copied next to the app. -->
+      <_CoreCLRAppLocalAssembly Include="@(ReferenceCopyLocalPaths)"
+                                Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(MicrosoftNetCoreAppRuntimePackDir)'))" />
+    </ItemGroup>
+    <PropertyGroup>
+      <_CoreCLRAppLocalAssemblyNames>;@(_CoreCLRAppLocalAssembly->'%(FileName)%(Extension)');</_CoreCLRAppLocalAssemblyNames>
+    </PropertyGroup>
+    <ItemGroup>
+      <!-- Drop runtime-pack copies shadowed by a same-named app-local assembly. -->
+      <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
+                               Condition="'%(Extension)' == '.dll'
+                                          and $([System.String]::Copy('%(FullPath)').StartsWith('$(MicrosoftNetCoreAppRuntimePackDir)'))
+                                          and $(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
+    </ItemGroup>
+  </Target>
+
   <!-- ======================== Core Orchestrator ======================== -->
 
   <PropertyGroup>

From 564acab1c1756bce783721cb319acecf083cd622 Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Mon, 15 Jun 2026 10:43:54 +0200
Subject: [PATCH 02/13] Feedback

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
---
 src/libraries/tests.proj | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/tests.proj b/src/libraries/tests.proj
index 3a733a0604e79f..c9711aff2d5bfb 100644
--- a/src/libraries/tests.proj
+++ b/src/libraries/tests.proj
@@ -183,7 +183,7 @@
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Runtime\tests\System.IO.FileSystem.Tests\DisabledFileLockingTests\System.IO.FileSystem.DisabledFileLocking.Tests.csproj" />
   </ItemGroup>
 
-  <!-- https://github.com/dotnet/runtime/issues/125495 - These tests are disabled on browser/CoreCLR because of crashes and test failures. -->
+  <!-- https://github.com/dotnet/runtime/issues/125495 - Some test suites are disabled on browser/CoreCLR (e.g., long running suites). -->
   <ItemGroup Condition="'$(TargetOS)' == 'browser' and '$(RuntimeFlavor)' == 'CoreCLR' and '$(RunDisabledWasmTests)' != 'true'">
     <!-- long running suites -->
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Linq\tests\System.Linq.Tests.csproj" />

From 1a4d41f993d16487f7ddfb646862eb8f4ce551ac Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Mon, 15 Jun 2026 10:49:01 +0200
Subject: [PATCH 03/13] Normalize runtime pack dir before StartsWith checks

$(MicrosoftNetCoreAppRuntimePackDir) is not normalized in this file (it can
come straight from %(ResolvedRuntimePack.PackageDirectory) or a global
property), so a missing trailing separator or non-native path separators could
make the StartsWith checks fail to identify runtime-pack assemblies, silently
skipping the dedupe. Normalize it once with [MSBuild]::NormalizeDirectory and
use that for both checks so it reliably matches %(FullPath).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/mono/browser/build/BrowserWasmApp.CoreCLR.targets | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index b83bf16ec25a33..b5a004c061f140 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -195,10 +195,15 @@
   <Target Name="_CoreCLRPreferAppLocalAssembliesOverRuntimePack"
           BeforeTargets="_ComputeWasmBuildCandidates;_GatherWasmFilesToBuild"
           Condition="'$(IsBrowserWasmProject)' == 'true' and '$(MicrosoftNetCoreAppRuntimePackDir)' != ''">
+    <PropertyGroup>
+      <!-- Normalize once (canonical separators + trailing slash) so the StartsWith checks below
+           reliably match %(FullPath), which uses native separators. -->
+      <_CoreCLRRuntimePackDirNormalized>$([MSBuild]::NormalizeDirectory('$(MicrosoftNetCoreAppRuntimePackDir)'))</_CoreCLRRuntimePackDirNormalized>
+    </PropertyGroup>
     <ItemGroup>
       <!-- App-local (non-runtime-pack) managed assemblies copied next to the app. -->
       <_CoreCLRAppLocalAssembly Include="@(ReferenceCopyLocalPaths)"
-                                Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(MicrosoftNetCoreAppRuntimePackDir)'))" />
+                                Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDirNormalized)'))" />
     </ItemGroup>
     <PropertyGroup>
       <_CoreCLRAppLocalAssemblyNames>;@(_CoreCLRAppLocalAssembly->'%(FileName)%(Extension)');</_CoreCLRAppLocalAssemblyNames>
@@ -207,7 +212,7 @@
       <!-- Drop runtime-pack copies shadowed by a same-named app-local assembly. -->
       <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
                                Condition="'%(Extension)' == '.dll'
-                                          and $([System.String]::Copy('%(FullPath)').StartsWith('$(MicrosoftNetCoreAppRuntimePackDir)'))
+                                          and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDirNormalized)'))
                                           and $(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
     </ItemGroup>
   </Target>

From df2f4e587d47288e1f1d852c4a0d6942c95bf066 Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Mon, 15 Jun 2026 12:07:12 +0200
Subject: [PATCH 04/13] Resolve runtime pack dir with ResolvedRuntimePack
 fallback

The target previously only ran when $(MicrosoftNetCoreAppRuntimePackDir) was
set, but WBT/Helix-created CoreCLR-wasm projects can leave that property empty
and rely on %(ResolvedRuntimePack.PackageDirectory) instead, so the target was
skipped and the runtime-pack vs app-local shadowing persisted for them.

Resolve the runtime pack dir inside the target the same way the WebAssembly SDK
does (Browser.targets): prefer the property, fall back to the ResolvedRuntimePack
metadata, then normalize. Both ItemGroups are guarded so an unresolved dir is a
safe no-op.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../build/BrowserWasmApp.CoreCLR.targets      | 20 +++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index b5a004c061f140..354e89cc9d903c 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -194,25 +194,29 @@
   -->
   <Target Name="_CoreCLRPreferAppLocalAssembliesOverRuntimePack"
           BeforeTargets="_ComputeWasmBuildCandidates;_GatherWasmFilesToBuild"
-          Condition="'$(IsBrowserWasmProject)' == 'true' and '$(MicrosoftNetCoreAppRuntimePackDir)' != ''">
+          Condition="'$(IsBrowserWasmProject)' == 'true'">
     <PropertyGroup>
-      <!-- Normalize once (canonical separators + trailing slash) so the StartsWith checks below
-           reliably match %(FullPath), which uses native separators. -->
-      <_CoreCLRRuntimePackDirNormalized>$([MSBuild]::NormalizeDirectory('$(MicrosoftNetCoreAppRuntimePackDir)'))</_CoreCLRRuntimePackDirNormalized>
+      <!-- Resolve the runtime pack dir the same way the WebAssembly SDK does (Browser.targets): prefer
+           the property, fall back to the ResolvedRuntimePack metadata (WBT/Helix-created projects leave
+           the property empty). Normalize once (full path + trailing slash) so the StartsWith checks
+           below reliably match %(FullPath), which uses native separators. -->
+      <_CoreCLRRuntimePackDir>$(MicrosoftNetCoreAppRuntimePackDir)</_CoreCLRRuntimePackDir>
+      <_CoreCLRRuntimePackDir Condition="'$(_CoreCLRRuntimePackDir)' == ''">%(ResolvedRuntimePack.PackageDirectory)</_CoreCLRRuntimePackDir>
+      <_CoreCLRRuntimePackDir Condition="'$(_CoreCLRRuntimePackDir)' != ''">$([MSBuild]::NormalizeDirectory('$(_CoreCLRRuntimePackDir)'))</_CoreCLRRuntimePackDir>
     </PropertyGroup>
-    <ItemGroup>
+    <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
       <!-- App-local (non-runtime-pack) managed assemblies copied next to the app. -->
       <_CoreCLRAppLocalAssembly Include="@(ReferenceCopyLocalPaths)"
-                                Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDirNormalized)'))" />
+                                Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)'))" />
     </ItemGroup>
     <PropertyGroup>
       <_CoreCLRAppLocalAssemblyNames>;@(_CoreCLRAppLocalAssembly->'%(FileName)%(Extension)');</_CoreCLRAppLocalAssemblyNames>
     </PropertyGroup>
-    <ItemGroup>
+    <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
       <!-- Drop runtime-pack copies shadowed by a same-named app-local assembly. -->
       <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
                                Condition="'%(Extension)' == '.dll'
-                                          and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDirNormalized)'))
+                                          and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)'))
                                           and $(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
     </ItemGroup>
   </Target>

From 58e4d6679f0f2195923eaadc1cfffb5e1d9ee597 Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Mon, 15 Jun 2026 15:37:20 +0200
Subject: [PATCH 05/13] Run dedupe after ResolveReferences to guarantee
 populated item list

_GatherWasmFilesToBuild has no DependsOnTargets, so a target hooked only
via BeforeTargets could run before ResolveReferences populates
@(ReferenceCopyLocalPaths), making the dedupe a no-op. Add
DependsOnTargets=ResolveReferences so the prune is correct-by-construction.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/mono/browser/build/BrowserWasmApp.CoreCLR.targets | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index 354e89cc9d903c..52dece99895f9c 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -191,9 +191,13 @@
     Resolve it the way a self-contained app loads assemblies (copy-local wins): drop runtime-pack copies
     shadowed by a same-named app-local copy before the candidates are gathered. Apps without an app-local
     copy of a framework assembly are unaffected.
+
+    DependsOnTargets=ResolveReferences guarantees @(ReferenceCopyLocalPaths) is populated before we prune;
+    _GatherWasmFilesToBuild (unlike _ComputeWasmBuildCandidates) does not pull it in on its own.
   -->
   <Target Name="_CoreCLRPreferAppLocalAssembliesOverRuntimePack"
           BeforeTargets="_ComputeWasmBuildCandidates;_GatherWasmFilesToBuild"
+          DependsOnTargets="ResolveReferences"
           Condition="'$(IsBrowserWasmProject)' == 'true'">
     <PropertyGroup>
       <!-- Resolve the runtime pack dir the same way the WebAssembly SDK does (Browser.targets): prefer

From 0c4f2fab41fad0fc1de64fa97f2925027ac442dd Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Tue, 23 Jun 2026 10:59:38 +0200
Subject: [PATCH 06/13] Make app-local vs runtime-pack resolution version-based

Replace the name-based "copy-local wins" rule with the SDK's own
ResolvePackageFileConflicts task so the higher AssemblyVersion wins,
matching desktop self-contained publish. This keeps the functional
System.Runtime.Serialization.Formatters 11.0.0.0 over the 8.1.0.0
framework stub in the wasm _framework bundle.

The task ships in every .NET SDK, so it resolves on user systems for
any Microsoft.NET.Sdk browser-wasm build, not just the in-repo build.
A name-based fallback (drop shadowed runtime-pack copies) is kept for
the unlikely case the SDK build-tasks assembly is unavailable.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../build/BrowserWasmApp.CoreCLR.targets      | 49 ++++++++++++++++---
 1 file changed, 43 insertions(+), 6 deletions(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index 52dece99895f9c..dc05ae512af4e3 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -178,6 +178,14 @@
                      '$(WasmBuildingForNestedPublish)' != 'true' and
                      '$(UsingBrowserRuntimeWorkload)' != 'true'" />
 
+  <!-- The SDK declares this in Microsoft.NET.ConflictResolution.targets for every Microsoft.NET.Sdk build
+       (which every browser-wasm app is). Re-declare it here, guarded, so the task resolves on user systems
+       regardless of import order; the guard also lets the target degrade gracefully where the SDK build
+       tasks assembly is unavailable. -->
+  <UsingTask TaskName="ResolvePackageFileConflicts"
+             AssemblyFile="$(MicrosoftNETBuildTasksAssembly)"
+             Condition="'$(MicrosoftNETBuildTasksAssembly)' != '' and Exists('$(MicrosoftNETBuildTasksAssembly)')" />
+
   <!-- ======================== Prefer app-local assemblies over runtime-pack copies ========================
 
     For a self-contained browser-wasm app, @(ReferenceCopyLocalPaths) can contain two copies of the
@@ -188,9 +196,17 @@
     shared framework ships a non-functional 8.1.0.0 stub while the app references the functional 11.0.0.0
     build, so an Assembly.Load for 11.0.0.0 then fails with FileNotFoundException.
 
-    Resolve it the way a self-contained app loads assemblies (copy-local wins): drop runtime-pack copies
-    shadowed by a same-named app-local copy before the candidates are gathered. Apps without an app-local
-    copy of a framework assembly are unaffected.
+    Resolve the shadowed pairs with the SDK's own conflict resolver (ResolvePackageFileConflicts) — the
+    same task SDK publish uses (Microsoft.NET.ConflictResolution.targets) — so the higher AssemblyVersion
+    wins, exactly as a desktop self-contained publish would. The wasm build path normally never reaches
+    that resolver for runtime-pack files, which is why the stub leaks into _framework. We feed the resolver
+    only the same-named runtime-pack/app-local pairs and drop whichever copies it discards; assemblies that
+    exist in just one place are untouched.
+
+    Robustness on user systems: ResolvePackageFileConflicts ships in the .NET SDK, so it is present for any
+    Microsoft.NET.Sdk browser-wasm build (in-repo or on a user machine). If the SDK build tasks assembly is
+    somehow unavailable, fall back to "copy-local wins" (drop the shadowed runtime-pack copies) so the fix
+    still applies — matching how a self-contained app loads assemblies.
 
     DependsOnTargets=ResolveReferences guarantees @(ReferenceCopyLocalPaths) is populated before we prune;
     _GatherWasmFilesToBuild (unlike _ComputeWasmBuildCandidates) does not pull it in on its own.
@@ -209,15 +225,36 @@
       <_CoreCLRRuntimePackDir Condition="'$(_CoreCLRRuntimePackDir)' != ''">$([MSBuild]::NormalizeDirectory('$(_CoreCLRRuntimePackDir)'))</_CoreCLRRuntimePackDir>
     </PropertyGroup>
     <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
-      <!-- App-local (non-runtime-pack) managed assemblies copied next to the app. -->
+      <!-- Split copy-local managed assemblies into app-local vs runtime-pack copies. -->
       <_CoreCLRAppLocalAssembly Include="@(ReferenceCopyLocalPaths)"
                                 Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)'))" />
+      <_CoreCLRRuntimePackAssembly Include="@(ReferenceCopyLocalPaths)"
+                                   Condition="'%(Extension)' == '.dll' and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)'))" />
     </ItemGroup>
-    <PropertyGroup>
+    <PropertyGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
       <_CoreCLRAppLocalAssemblyNames>;@(_CoreCLRAppLocalAssembly->'%(FileName)%(Extension)');</_CoreCLRAppLocalAssemblyNames>
+      <_CoreCLRRuntimePackAssemblyNames>;@(_CoreCLRRuntimePackAssembly->'%(FileName)%(Extension)');</_CoreCLRRuntimePackAssemblyNames>
     </PropertyGroup>
     <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
-      <!-- Drop runtime-pack copies shadowed by a same-named app-local assembly. -->
+      <!-- The conflict set: copies of the same file name present in BOTH the runtime pack and app-local. -->
+      <_CoreCLRConflictCandidate Include="@(_CoreCLRRuntimePackAssembly)"
+                                 Condition="$(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
+      <_CoreCLRConflictCandidate Include="@(_CoreCLRAppLocalAssembly)"
+                                 Condition="$(_CoreCLRRuntimePackAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
+    </ItemGroup>
+
+    <!-- Version-based resolution (parity with SDK publish/desktop): keep the higher AssemblyVersion. -->
+    <ResolvePackageFileConflicts Condition="'@(_CoreCLRConflictCandidate)' != '' and Exists('$(MicrosoftNETBuildTasksAssembly)')"
+                                 ReferenceCopyLocalPaths="@(_CoreCLRConflictCandidate)">
+      <Output TaskParameter="ReferenceCopyLocalPathsWithoutConflicts" ItemName="_CoreCLRConflictWinners" />
+    </ResolvePackageFileConflicts>
+    <ItemGroup Condition="'@(_CoreCLRConflictCandidate)' != '' and Exists('$(MicrosoftNETBuildTasksAssembly)')">
+      <_CoreCLRConflictLoser Include="@(_CoreCLRConflictCandidate)" Exclude="@(_CoreCLRConflictWinners)" />
+      <ReferenceCopyLocalPaths Remove="@(_CoreCLRConflictLoser)" />
+    </ItemGroup>
+
+    <!-- Fallback when the SDK conflict-resolution task is unavailable: prefer app-local (copy-local wins). -->
+    <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != '' and '@(_CoreCLRConflictCandidate)' != '' and !Exists('$(MicrosoftNETBuildTasksAssembly)')">
       <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
                                Condition="'%(Extension)' == '.dll'
                                           and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)'))

From 6761dde993c94405ece301490f1ec98a2df0e78e Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Tue, 23 Jun 2026 12:18:50 +0200
Subject: [PATCH 07/13] Pass PreferredPackages for exact tie parity with
 publish
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Feed $(PackageConflictPreferredPackages) into the ResolvePackageFileConflicts
call so an exact AssemblyVersion+FileVersion tie is broken the same way the
SDK publish target (_HandlePackageFileConflictsForPublish) breaks it —
preferring the framework runtime-pack package — instead of leaving the tie to
the downstream first-wins webcil dedup. The property is populated by
ResolveTargetingPackAssets, which runs as part of the ResolveReferences
dependency, so it is available when this target executes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/mono/browser/build/BrowserWasmApp.CoreCLR.targets | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index dc05ae512af4e3..8ad9a054616ef5 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -243,9 +243,14 @@
                                  Condition="$(_CoreCLRRuntimePackAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
     </ItemGroup>
 
-    <!-- Version-based resolution (parity with SDK publish/desktop): keep the higher AssemblyVersion. -->
+    <!-- Version-based resolution (parity with SDK publish/desktop): keep the higher AssemblyVersion.
+         PreferredPackages mirrors the SDK publish call (_HandlePackageFileConflictsForPublish) so that an
+         exact AssemblyVersion+FileVersion tie is broken the same way publish breaks it (preferring the
+         framework package) instead of being left to the downstream first-wins dedup. The property is
+         populated by ResolveTargetingPackAssets, which runs as part of our ResolveReferences dependency. -->
     <ResolvePackageFileConflicts Condition="'@(_CoreCLRConflictCandidate)' != '' and Exists('$(MicrosoftNETBuildTasksAssembly)')"
-                                 ReferenceCopyLocalPaths="@(_CoreCLRConflictCandidate)">
+                                 ReferenceCopyLocalPaths="@(_CoreCLRConflictCandidate)"
+                                 PreferredPackages="$(PackageConflictPreferredPackages)">
       <Output TaskParameter="ReferenceCopyLocalPathsWithoutConflicts" ItemName="_CoreCLRConflictWinners" />
     </ResolvePackageFileConflicts>
     <ItemGroup Condition="'@(_CoreCLRConflictCandidate)' != '' and Exists('$(MicrosoftNETBuildTasksAssembly)')">

From a94dc001369623f059c7f4f021e95b1e7ffa2dff Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Tue, 23 Jun 2026 13:12:33 +0200
Subject: [PATCH 08/13] Use OrdinalIgnoreCase for runtime-pack path/name
 comparisons

The StartsWith path-prefix checks and the Contains name-membership checks
were ordinal case-sensitive. On a case-insensitive filesystem a casing
difference between $(MicrosoftNetCoreAppRuntimePackDir) and the enumerated
%(FullPath) values (e.g. drive-letter or user-overridden casing) could
silently misclassify a runtime-pack copy as app-local and no-op the fix
with no error. Compare with System.StringComparison.OrdinalIgnoreCase so
classification is robust, matching how the SDK itself does path-prefix
checks (e.g. Microsoft.FSharp.Targets).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../browser/build/BrowserWasmApp.CoreCLR.targets | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index 8ad9a054616ef5..cacc7831d27703 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -219,7 +219,9 @@
       <!-- Resolve the runtime pack dir the same way the WebAssembly SDK does (Browser.targets): prefer
            the property, fall back to the ResolvedRuntimePack metadata (WBT/Helix-created projects leave
            the property empty). Normalize once (full path + trailing slash) so the StartsWith checks
-           below reliably match %(FullPath), which uses native separators. -->
+           below reliably match %(FullPath), which uses native separators. The path/name comparisons
+           use OrdinalIgnoreCase so a casing difference between the property and the enumerated item
+           paths (common on case-insensitive filesystems) cannot silently misclassify a copy. -->
       <_CoreCLRRuntimePackDir>$(MicrosoftNetCoreAppRuntimePackDir)</_CoreCLRRuntimePackDir>
       <_CoreCLRRuntimePackDir Condition="'$(_CoreCLRRuntimePackDir)' == ''">%(ResolvedRuntimePack.PackageDirectory)</_CoreCLRRuntimePackDir>
       <_CoreCLRRuntimePackDir Condition="'$(_CoreCLRRuntimePackDir)' != ''">$([MSBuild]::NormalizeDirectory('$(_CoreCLRRuntimePackDir)'))</_CoreCLRRuntimePackDir>
@@ -227,9 +229,9 @@
     <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
       <!-- Split copy-local managed assemblies into app-local vs runtime-pack copies. -->
       <_CoreCLRAppLocalAssembly Include="@(ReferenceCopyLocalPaths)"
-                                Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)'))" />
+                                Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))" />
       <_CoreCLRRuntimePackAssembly Include="@(ReferenceCopyLocalPaths)"
-                                   Condition="'%(Extension)' == '.dll' and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)'))" />
+                                   Condition="'%(Extension)' == '.dll' and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))" />
     </ItemGroup>
     <PropertyGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
       <_CoreCLRAppLocalAssemblyNames>;@(_CoreCLRAppLocalAssembly->'%(FileName)%(Extension)');</_CoreCLRAppLocalAssemblyNames>
@@ -238,9 +240,9 @@
     <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
       <!-- The conflict set: copies of the same file name present in BOTH the runtime pack and app-local. -->
       <_CoreCLRConflictCandidate Include="@(_CoreCLRRuntimePackAssembly)"
-                                 Condition="$(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
+                                 Condition="$(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase))" />
       <_CoreCLRConflictCandidate Include="@(_CoreCLRAppLocalAssembly)"
-                                 Condition="$(_CoreCLRRuntimePackAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
+                                 Condition="$(_CoreCLRRuntimePackAssemblyNames.Contains(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase))" />
     </ItemGroup>
 
     <!-- Version-based resolution (parity with SDK publish/desktop): keep the higher AssemblyVersion.
@@ -262,8 +264,8 @@
     <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != '' and '@(_CoreCLRConflictCandidate)' != '' and !Exists('$(MicrosoftNETBuildTasksAssembly)')">
       <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
                                Condition="'%(Extension)' == '.dll'
-                                          and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)'))
-                                          and $(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
+                                          and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))
+                                          and $(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase))" />
     </ItemGroup>
   </Target>
 

From bc486ecb31c317421ab9df7040ad3d26fe0b2ae6 Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Tue, 23 Jun 2026 15:06:35 +0200
Subject: [PATCH 09/13] Apply suggestions from code review

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
---
 src/mono/browser/build/BrowserWasmApp.CoreCLR.targets | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index cacc7831d27703..71785730b5aa55 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -240,9 +240,9 @@
     <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
       <!-- The conflict set: copies of the same file name present in BOTH the runtime pack and app-local. -->
       <_CoreCLRConflictCandidate Include="@(_CoreCLRRuntimePackAssembly)"
-                                 Condition="$(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase))" />
+                                 Condition="$(_CoreCLRAppLocalAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase) != -1)" />
       <_CoreCLRConflictCandidate Include="@(_CoreCLRAppLocalAssembly)"
-                                 Condition="$(_CoreCLRRuntimePackAssemblyNames.Contains(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase))" />
+                                 Condition="$(_CoreCLRRuntimePackAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase) != -1)" />
     </ItemGroup>
 
     <!-- Version-based resolution (parity with SDK publish/desktop): keep the higher AssemblyVersion.
@@ -265,7 +265,7 @@
       <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
                                Condition="'%(Extension)' == '.dll'
                                           and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))
-                                          and $(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase))" />
+                                          and $(_CoreCLRAppLocalAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase) != -1)" />
     </ItemGroup>
   </Target>
 

From 2949e87e512faebb0537ad819877be4d87f5f0de Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Tue, 23 Jun 2026 15:43:01 +0200
Subject: [PATCH 10/13] Update target comment to reflect version-based
 resolution

The section header still described the target as unconditionally preferring
app-local assemblies over runtime-pack copies, but the resolution is now
version-based via ResolvePackageFileConflicts (publish parity), where the
runtime-pack copy can legitimately win when it has the higher version. Reword
the banner and body so the comment matches the implementation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../build/BrowserWasmApp.CoreCLR.targets      | 21 ++++++++++---------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index 71785730b5aa55..a6abcd244be8d9 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -186,26 +186,27 @@
              AssemblyFile="$(MicrosoftNETBuildTasksAssembly)"
              Condition="'$(MicrosoftNETBuildTasksAssembly)' != '' and Exists('$(MicrosoftNETBuildTasksAssembly)')" />
 
-  <!-- ======================== Prefer app-local assemblies over runtime-pack copies ========================
+  <!-- ==================== Resolve runtime-pack vs app-local assembly conflicts by version ====================
 
     For a self-contained browser-wasm app, @(ReferenceCopyLocalPaths) can contain two copies of the
     same assembly: the runtime-pack copy (under $(MicrosoftNetCoreAppRuntimePackDir)) and an app-local
     copy referenced out-of-band at a different version. ComputeWasmBuildAssets dedupes the webcil bundle
-    candidates by relative path (first-wins, version-blind), so the runtime-pack copy can shadow the
-    app-local one in _framework. The canonical case is System.Runtime.Serialization.Formatters: the
-    shared framework ships a non-functional 8.1.0.0 stub while the app references the functional 11.0.0.0
-    build, so an Assembly.Load for 11.0.0.0 then fails with FileNotFoundException.
+    candidates by relative path (first-wins, version-blind), so the wrong copy can shadow the other one
+    in _framework. The canonical case is System.Runtime.Serialization.Formatters: the shared framework
+    ships a non-functional 8.1.0.0 stub while the app references the functional 11.0.0.0 build, so an
+    Assembly.Load for 11.0.0.0 then fails with FileNotFoundException.
 
     Resolve the shadowed pairs with the SDK's own conflict resolver (ResolvePackageFileConflicts) — the
     same task SDK publish uses (Microsoft.NET.ConflictResolution.targets) — so the higher AssemblyVersion
-    wins, exactly as a desktop self-contained publish would. The wasm build path normally never reaches
-    that resolver for runtime-pack files, which is why the stub leaks into _framework. We feed the resolver
-    only the same-named runtime-pack/app-local pairs and drop whichever copies it discards; assemblies that
-    exist in just one place are untouched.
+    wins, exactly as a desktop self-contained publish would. This is version-based, not an unconditional
+    app-local preference: when the runtime-pack copy is the higher version it is the one that is kept. The
+    wasm build path normally never reaches that resolver for runtime-pack files, which is why the stub
+    leaks into _framework. We feed the resolver only the same-named runtime-pack/app-local pairs and drop
+    whichever copies it discards; assemblies that exist in just one place are untouched.
 
     Robustness on user systems: ResolvePackageFileConflicts ships in the .NET SDK, so it is present for any
     Microsoft.NET.Sdk browser-wasm build (in-repo or on a user machine). If the SDK build tasks assembly is
-    somehow unavailable, fall back to "copy-local wins" (drop the shadowed runtime-pack copies) so the fix
+    somehow unavailable, fall back to "app-local wins" (drop the shadowed runtime-pack copies) so the fix
     still applies — matching how a self-contained app loads assemblies.
 
     DependsOnTargets=ResolveReferences guarantees @(ReferenceCopyLocalPaths) is populated before we prune;

From b0454371772afb66494a31d813065f9024a88397 Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Tue, 23 Jun 2026 16:48:46 +0200
Subject: [PATCH 11/13] Rename target to reflect version-based conflict
 resolution

_CoreCLRPreferAppLocalAssembliesOverRuntimePack implied app-local always
wins, but the target resolves runtime-pack vs app-local conflicts by version
(publish parity), where the runtime-pack copy can win when it is the higher
version. Rename to _CoreCLRResolveRuntimePackVsAppLocalConflicts to match.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/mono/browser/build/BrowserWasmApp.CoreCLR.targets | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index a6abcd244be8d9..49cecf63434f54 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -212,7 +212,7 @@
     DependsOnTargets=ResolveReferences guarantees @(ReferenceCopyLocalPaths) is populated before we prune;
     _GatherWasmFilesToBuild (unlike _ComputeWasmBuildCandidates) does not pull it in on its own.
   -->
-  <Target Name="_CoreCLRPreferAppLocalAssembliesOverRuntimePack"
+  <Target Name="_CoreCLRResolveRuntimePackVsAppLocalConflicts"
           BeforeTargets="_ComputeWasmBuildCandidates;_GatherWasmFilesToBuild"
           DependsOnTargets="ResolveReferences"
           Condition="'$(IsBrowserWasmProject)' == 'true'">

From 06eb820bfc08790486d1483522b6c26acb50f0c0 Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Wed, 24 Jun 2026 12:02:10 +0200
Subject: [PATCH 12/13] Fix MSB4184 from comparison operator inside $() in
 conflict conditions

The case-insensitive name membership checks used
$(list.IndexOf(';name;', System.StringComparison.OrdinalIgnoreCase) != -1).
MSBuild's property-function expander evaluates a method-call chain and returns
its value, but it rejects a trailing comparison operator (!= -1, >= 0) placed
inside the $(), raising error MSB4184 "cannot be evaluated". This is independent
of the StringComparison argument and of the item/metadata context, and it broke
the wasm CoreCLR build for every library test project (e.g. System.Runtime.Tests).
Contains(string, StringComparison) sidesteps it (returns bool directly) but that
overload is missing on .NET Framework MSBuild.

Keep IndexOf(string, StringComparison) with OrdinalIgnoreCase (available on .NET
Framework 2.0+) and move the "!= -1" test OUTSIDE the $() so it is a top-level
Condition comparison on the returned int. This preserves the original
case-insensitive intent, stays consistent with the StartsWith(..., OrdinalIgnoreCase)
path checks, and needs no lower-casing workaround.

Validated: Nrbf wasm CoreCLR suite builds 0 warnings/0 errors and runs 4/4 passing
from a freshly pruned bundle; the target's ResolvePackageFileConflicts picks
Formatters 11.0.0.0 over the 8.1.0.0 stub by AssemblyVersion.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../build/BrowserWasmApp.CoreCLR.targets      | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index 49cecf63434f54..3c768808310df9 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -220,9 +220,14 @@
       <!-- Resolve the runtime pack dir the same way the WebAssembly SDK does (Browser.targets): prefer
            the property, fall back to the ResolvedRuntimePack metadata (WBT/Helix-created projects leave
            the property empty). Normalize once (full path + trailing slash) so the StartsWith checks
-           below reliably match %(FullPath), which uses native separators. The path/name comparisons
-           use OrdinalIgnoreCase so a casing difference between the property and the enumerated item
-           paths (common on case-insensitive filesystems) cannot silently misclassify a copy. -->
+           below reliably match %(FullPath), which uses native separators. All comparisons use the
+           OrdinalIgnoreCase StringComparison so a casing difference between the property and the
+           enumerated item paths (common on case-insensitive filesystems) cannot silently misclassify a
+           copy. Path membership uses StartsWith(string, StringComparison); name membership uses
+           IndexOf(string, StringComparison) with the "!= -1" test kept OUTSIDE the $() (MSBuild's
+           property-function expander returns the int index but rejects a trailing comparison operator
+           inside the $(), which is the MSB4184 trap). Both overloads exist on .NET Framework MSBuild;
+           the Contains(string, StringComparison) overload does not, so it is avoided. -->
       <_CoreCLRRuntimePackDir>$(MicrosoftNetCoreAppRuntimePackDir)</_CoreCLRRuntimePackDir>
       <_CoreCLRRuntimePackDir Condition="'$(_CoreCLRRuntimePackDir)' == ''">%(ResolvedRuntimePack.PackageDirectory)</_CoreCLRRuntimePackDir>
       <_CoreCLRRuntimePackDir Condition="'$(_CoreCLRRuntimePackDir)' != ''">$([MSBuild]::NormalizeDirectory('$(_CoreCLRRuntimePackDir)'))</_CoreCLRRuntimePackDir>
@@ -235,15 +240,17 @@
                                    Condition="'%(Extension)' == '.dll' and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))" />
     </ItemGroup>
     <PropertyGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
+      <!-- ;-delimited name lists wrapped in leading/trailing ';' so an IndexOf of ';name;' below is an
+           exact whole-name membership test (never a substring of a longer name). -->
       <_CoreCLRAppLocalAssemblyNames>;@(_CoreCLRAppLocalAssembly->'%(FileName)%(Extension)');</_CoreCLRAppLocalAssemblyNames>
       <_CoreCLRRuntimePackAssemblyNames>;@(_CoreCLRRuntimePackAssembly->'%(FileName)%(Extension)');</_CoreCLRRuntimePackAssemblyNames>
     </PropertyGroup>
     <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
       <!-- The conflict set: copies of the same file name present in BOTH the runtime pack and app-local. -->
       <_CoreCLRConflictCandidate Include="@(_CoreCLRRuntimePackAssembly)"
-                                 Condition="$(_CoreCLRAppLocalAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase) != -1)" />
+                                 Condition="$(_CoreCLRAppLocalAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase)) != -1" />
       <_CoreCLRConflictCandidate Include="@(_CoreCLRAppLocalAssembly)"
-                                 Condition="$(_CoreCLRRuntimePackAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase) != -1)" />
+                                 Condition="$(_CoreCLRRuntimePackAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase)) != -1" />
     </ItemGroup>
 
     <!-- Version-based resolution (parity with SDK publish/desktop): keep the higher AssemblyVersion.
@@ -266,7 +273,7 @@
       <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
                                Condition="'%(Extension)' == '.dll'
                                           and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))
-                                          and $(_CoreCLRAppLocalAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase) != -1)" />
+                                          and $(_CoreCLRAppLocalAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase)) != -1" />
     </ItemGroup>
   </Target>
 

From cc0f86877356310ca16c22d128b16ed63c0fea5c Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Wed, 24 Jun 2026 12:49:31 +0200
Subject: [PATCH 13/13] Harden wasm conflict resolution per code review

Address multi-model review findings on the runtime-pack vs app-local
conflict-resolution target:

- Restrict the conflict set to assemblies that deploy to the _framework
  root (empty DestinationSubDirectory/Culture). The bundle is keyed on a
  culture-qualified RelativePath, so same-named satellites in different
  cultures never collide; matching by file name alone could wrongly prune
  a runtime-pack satellite. Qualify the metadata references so items that
  lack DestinationSubDirectory/Culture don't trip MSB4096.

- Drop the discarded copies the way the SDK's _HandlePackageFileConflicts
  does (remove every candidate, then re-add the winners) instead of
  removing an Exclude-derived loser subset. ReferenceCopyLocalPaths
  removal matches on ItemSpec only, so re-including the winners (which
  carry full metadata) is the robust, lossless form.

- Note the single-runtime-pack invariant the ResolvedRuntimePack metadata
  fallback relies on, matching the WebAssembly SDK's Browser.targets.

Validated: clean browser-wasm CoreCLR build of System.Formats.Nrbf.Tests,
0 warnings/0 errors, 4/4 tests pass (WASM EXIT 0); binlog confirms the
functional 11.0.0.0 Formatters wins over the 8.1.0.0 stub.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../build/BrowserWasmApp.CoreCLR.targets      | 45 +++++++++++++------
 1 file changed, 31 insertions(+), 14 deletions(-)

diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index 3c768808310df9..b0d74340c6c7d9 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -201,8 +201,9 @@
     wins, exactly as a desktop self-contained publish would. This is version-based, not an unconditional
     app-local preference: when the runtime-pack copy is the higher version it is the one that is kept. The
     wasm build path normally never reaches that resolver for runtime-pack files, which is why the stub
-    leaks into _framework. We feed the resolver only the same-named runtime-pack/app-local pairs and drop
-    whichever copies it discards; assemblies that exist in just one place are untouched.
+    leaks into _framework. We feed the resolver only the same-named runtime-pack/app-local pairs that deploy
+    to the _framework root (no culture subdirectory) and drop whichever copies it discards; assemblies that
+    exist in just one place, and culture-specific satellites, are untouched.
 
     Robustness on user systems: ResolvePackageFileConflicts ships in the .NET SDK, so it is present for any
     Microsoft.NET.Sdk browser-wasm build (in-repo or on a user machine). If the SDK build tasks assembly is
@@ -219,12 +220,14 @@
     <PropertyGroup>
       <!-- Resolve the runtime pack dir the same way the WebAssembly SDK does (Browser.targets): prefer
            the property, fall back to the ResolvedRuntimePack metadata (WBT/Helix-created projects leave
-           the property empty). Normalize once (full path + trailing slash) so the StartsWith checks
-           below reliably match %(FullPath), which uses native separators. All comparisons use the
-           OrdinalIgnoreCase StringComparison so a casing difference between the property and the
-           enumerated item paths (common on case-insensitive filesystems) cannot silently misclassify a
-           copy. Path membership uses StartsWith(string, StringComparison); name membership uses
-           IndexOf(string, StringComparison) with the "!= -1" test kept OUTSIDE the $() (MSBuild's
+           the property empty). A browser-wasm CoreCLR app resolves exactly one runtime pack
+           (Microsoft.NETCore.App), so the metadata expansion is unambiguous — the same single-pack
+           assumption the SDK's own Browser.targets relies on. Normalize once (full path + trailing slash)
+           so the StartsWith checks below reliably match %(FullPath), which uses native separators. All
+           comparisons use the OrdinalIgnoreCase StringComparison so a casing difference between the
+           property and the enumerated item paths (common on case-insensitive filesystems) cannot silently
+           misclassify a copy. Path membership uses StartsWith(string, StringComparison); name membership
+           uses IndexOf(string, StringComparison) with the "!= -1" test kept OUTSIDE the $() (MSBuild's
            property-function expander returns the int index but rejects a trailing comparison operator
            inside the $(), which is the MSB4184 trap). Both overloads exist on .NET Framework MSBuild;
            the Contains(string, StringComparison) overload does not, so it is avoided. -->
@@ -233,11 +236,17 @@
       <_CoreCLRRuntimePackDir Condition="'$(_CoreCLRRuntimePackDir)' != ''">$([MSBuild]::NormalizeDirectory('$(_CoreCLRRuntimePackDir)'))</_CoreCLRRuntimePackDir>
     </PropertyGroup>
     <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
-      <!-- Split copy-local managed assemblies into app-local vs runtime-pack copies. -->
+      <!-- Split copy-local managed assemblies into app-local vs runtime-pack copies. Restrict both sets to
+           assemblies that deploy to the _framework root: ComputeWasmBuildAssets keys the bundle on a culture-
+           qualified RelativePath (_framework/<culture>/<name> for satellites, _framework/<name> otherwise), so
+           same-named satellites in different cultures never actually collide. Matching the conflict set only by
+           file name would wrongly pair them, so we exclude anything with a culture/subdirectory (empty
+           DestinationSubDirectory and Culture == root deployment). Satellite-vs-satellite version skew is out of
+           scope here and is left to the downstream first-wins dedup. -->
       <_CoreCLRAppLocalAssembly Include="@(ReferenceCopyLocalPaths)"
-                                Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))" />
+                                Condition="'%(Extension)' == '.dll' and '%(ReferenceCopyLocalPaths.DestinationSubDirectory)' == '' and '%(ReferenceCopyLocalPaths.Culture)' == '' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))" />
       <_CoreCLRRuntimePackAssembly Include="@(ReferenceCopyLocalPaths)"
-                                   Condition="'%(Extension)' == '.dll' and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))" />
+                                   Condition="'%(Extension)' == '.dll' and '%(ReferenceCopyLocalPaths.DestinationSubDirectory)' == '' and '%(ReferenceCopyLocalPaths.Culture)' == '' and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))" />
     </ItemGroup>
     <PropertyGroup Condition="'$(_CoreCLRRuntimePackDir)' != ''">
       <!-- ;-delimited name lists wrapped in leading/trailing ';' so an IndexOf of ';name;' below is an
@@ -263,15 +272,23 @@
                                  PreferredPackages="$(PackageConflictPreferredPackages)">
       <Output TaskParameter="ReferenceCopyLocalPathsWithoutConflicts" ItemName="_CoreCLRConflictWinners" />
     </ResolvePackageFileConflicts>
+    <!-- Drop the discarded copies. Mirror the SDK's _HandlePackageFileConflicts (remove every candidate, then
+         re-add the winners) instead of removing a computed "loser" subset by identity: @(ReferenceCopyLocalPaths)
+         removal matches on ItemSpec only, so an Exclude-derived loser list is fragile if an ItemSpec ever repeats
+         with different metadata. ReferenceCopyLocalPathsWithoutConflicts carries the winners' full metadata, so
+         re-including them is lossless, and removing both candidate copies first guarantees the loser is gone. -->
     <ItemGroup Condition="'@(_CoreCLRConflictCandidate)' != '' and Exists('$(MicrosoftNETBuildTasksAssembly)')">
-      <_CoreCLRConflictLoser Include="@(_CoreCLRConflictCandidate)" Exclude="@(_CoreCLRConflictWinners)" />
-      <ReferenceCopyLocalPaths Remove="@(_CoreCLRConflictLoser)" />
+      <ReferenceCopyLocalPaths Remove="@(_CoreCLRConflictCandidate)" />
+      <ReferenceCopyLocalPaths Include="@(_CoreCLRConflictWinners)" />
     </ItemGroup>
 
-    <!-- Fallback when the SDK conflict-resolution task is unavailable: prefer app-local (copy-local wins). -->
+    <!-- Fallback when the SDK conflict-resolution task is unavailable: prefer app-local (copy-local wins). Same
+         root-only restriction as the split above so a runtime-pack satellite is never removed on a bare file-name
+         match against an unrelated app-local satellite in a different culture. -->
     <ItemGroup Condition="'$(_CoreCLRRuntimePackDir)' != '' and '@(_CoreCLRConflictCandidate)' != '' and !Exists('$(MicrosoftNETBuildTasksAssembly)')">
       <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
                                Condition="'%(Extension)' == '.dll'
+                                          and '%(ReferenceCopyLocalPaths.DestinationSubDirectory)' == '' and '%(ReferenceCopyLocalPaths.Culture)' == ''
                                           and $([System.String]::Copy('%(FullPath)').StartsWith('$(_CoreCLRRuntimePackDir)', System.StringComparison.OrdinalIgnoreCase))
                                           and $(_CoreCLRAppLocalAssemblyNames.IndexOf(';%(FileName)%(Extension);', System.StringComparison.OrdinalIgnoreCase)) != -1" />
     </ItemGroup>