AppNotificationManager.Register() still throws 0x8007007E (missing Microsoft.WindowsAppRuntime.Insights.Resource.dll) in self-contained unpackaged apps on 2.5.1; #6071 closed by #6725 but not fixed

[GenerAhl]

Describe the bug

AppNotificationManager.Default.Register() in an unpackaged, self-contained app still throws on Windows App SDK 2.5.1:

System.Runtime.InteropServices.COMException (0x8007007E): The specified module could not be found.

Unable to load resource dll. Microsoft.WindowsAppRuntime.Insights.Resource.dll
   at WinRT.ExceptionHelpers.ThrowExceptionForHR(Int32 hr)
   at ABI.Microsoft.Windows.AppNotifications.IAppNotificationManagerMethods.Register(IObjectReference _obj)
   at Microsoft.Windows.AppNotifications.AppNotificationManager.Register()

This is the failure from #6071. That issue was closed on 2026-09-03 by PR #6725 ("Fix errors from missing resource dll with version info", which also lists #6387), but the released packages do not behave as fixed. Several people on #6071 have reported the same on 2.3.1, 2.4.0 and 2.5.1 since. Filing separately because comments on a closed issue may not reach triage.

What makes this confusing:

• PR Fix errors from missing resource dll with version info #6725's merge commit (6b178e79) is an ancestor of the v2.5.1 tag (git compare says v2.5.1 is ahead of it; v2.4.0 and v2.4.1-exp are behind it).
• Microsoft.WindowsAppSDK.Foundation 2.3.12, which 2.5.1 depends on, was published to NuGet on 2026-09-16, after the merge.
• In the v2.5.1 source, AppNotificationManager::RegisterUnpackagedApp calls WindowsAppRuntime::SelfContained::IsSelfContained(), and WindowsAppRuntime_IsSelfContained now returns TRUE when WindowsAppRuntime_VersionInfo_MSIX_Framework_PackageFamilyName_Get returns ERROR_MOD_NOT_FOUND. On paper that should stop this exact exception.
• Yet Register() still throws 0x8007007E.

I could not find out why. Either the shipped native binary does not contain the fix, or another call site on the Register() path still throws on the missing DLL. I only have the managed stack above, no native stack.

Steps to reproduce the bug

Minimal project, no other code:

Repro.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net10.0-windows10.0.19041.0</TargetFramework>
    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
    <WindowsPackageType>None</WindowsPackageType>
    <WindowsAppSDKSelfContained>true</WindowsAppSDKSelfContained>
    <SelfContained>true</SelfContained>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.WindowsAppSDK" Version="2.5.1" />
  </ItemGroup>
</Project>

Program.cs

using System;
using Microsoft.Windows.AppNotifications;

try
{
    AppNotificationManager.Default.Register();
    Console.WriteLine("Register() succeeded");
}
catch (Exception ex)
{
    Console.WriteLine($"Register() threw {ex.GetType().Name} 0x{ex.HResult:X8}: {ex.Message}");
}

dotnet publish -c Release -o out
out\Repro.exe

Output on 2.5.1:

Register() threw COMException 0x8007007E: The specified module could not be found.

Unable to load resource dll. Microsoft.WindowsAppRuntime.Insights.Resource.dll

The same project on 2.4.0 fails identically. In our real app (a small helper that shows a notification, self-contained and single-file), I ran 2.4.0 as a control and 2.5.1 side by side and got the same exception from both; the toast itself still displays via Show(), but the activation registration fails, so NotificationInvoked is never raised for button clicks.

The extracted/published output contains Microsoft.WindowsAppRuntime.dll, Microsoft.WindowsAppRuntime.Bootstrap.dll and Microsoft.WindowsAppRuntime.Bootstrap.Net.dll, but no Microsoft.WindowsAppRuntime.Insights.Resource.dll.

Expected behavior

Per the description of #6725, a self-contained app that only uses component packages (no framework/runtime package) should be treated as self-contained when the resource DLL is absent, and Register() should succeed (or at least not throw because of it).

NuGet package version

Microsoft.WindowsAppSDK 2.5.1 (resolved: Foundation 2.3.12, Runtime 2.5.1). Also reproduces on 2.4.0.

Packaging type

Unpackaged

Windows version

Windows 11 25H2 (10.0.26200.9457), x64

IDE

Other (dotnet CLI, .NET SDK 10)

Additional context

• Related: Cannot register AppNotification callback without installing Runtime package for Self-Contained Unpackaged app #6071 (closed), Microsoft.WindowsAppRuntime.Insights.Resource.dll missing from Foundation package #6387, PR Fix errors from missing resource dll with version info #6725.
• Workaround per Cannot register AppNotification callback without installing Runtime package for Self-Contained Unpackaged app #6071: install the Windows App SDK Runtime (defeats the purpose of self-contained), or catch the exception and accept that activation callbacks will not be delivered.
• The system locale is Swedish; the Det går inte att hitta den angivna modulen text in raw logs is the localized form of the message above.