打包MSIX时AppService出现AppUnavailable的问题排查（附最小复现示例）

我最近碰到一个棘手的问题，先给大家梳理下我的项目结构：

/
└── MyApp.Package.wapproj → WAP项目，负责将MyApp.Win打包为MSIX
└── MyApp.Win.csproj → Avalonia net8.0-windows10.0.19041.0项目
├── MyApp.Shared.csproj → 共享的Avalonia .NET 8.0项目
└── AppService-RuntimeComponent.csproj → net8.0-windows10.0.19041.0的UWP Runtime Component，用于托管后台任务并暴露AppService

这个结构是参考WASDKSample搭建的，在Visual Studio里不管是Debug还是Release模式直接部署运行，AppService都能正常建立连接，完全没毛病。但当我用**Publish -> Create app packages...**工具把WAP项目打包成MSIX并安装后，我的AppService测试客户端连接时就会触发AppUnavailable状态。

我已经检查过生成的MSIX包，里面AppService-RuntimeComponent.dll和WinRT.Host.dll都存在，文件没丢失，那为啥VS直接部署和MSIX安装后的表现会不一样呢？

我的Package.appxmanifest内容如下：

<?xml version="1.0" encoding="utf-8"?>
<Package xmlns="http://schemas.microsoft.com/appx/manifest/foundation/windows10" 
         xmlns:uap="http://schemas.microsoft.com/appx/manifest/uap/windows10" 
         xmlns:desktop="http://schemas.microsoft.com/appx/manifest/desktop/windows10" 
         xmlns:rescap="http://schemas.microsoft.com/appx/manifest/foundation/windows10/restrictedcapabilities" 
         xmlns:uap3="http://schemas.microsoft.com/appx/manifest/uap/windows10/3" 
         xmlns:uap4="http://schemas.microsoft.com/appx/manifest/uap/windows10/4" 
         IgnorableNamespaces="uap uap3 uap4 rescap">
  <Identity Name="XXXXXXXXXXXXXXXXX" Publisher="CN=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX" Version="3.0.1.0" />
  <Properties>
    <DisplayName>XXXXXXXXXXXXXXXXXXXXX</DisplayName>
    <PublisherDisplayName>XXXXXXXXXXXXXXXXXXXX</PublisherDisplayName>
    <Logo>Assets\StoreLogo.png</Logo>
  </Properties>
  <Dependencies>
    <TargetDeviceFamily Name="Windows.Desktop" MinVersion="10.0.19041.0" MaxVersionTested="10.0.19041.0" />
  </Dependencies>
  <Resources>
    <Resource Language="x-generate"/>
  </Resources>
  <Applications>
    <Application Id="App" Executable="$targetnametoken$.exe" EntryPoint="Windows.FullTrustApplication">
      <uap:VisualElements DisplayName="XXXXXXXXXXXXX" Description="XXXXXXXXXXXXXXXXXXXX" BackgroundColor="transparent" Square150x150Logo="Assets\Square150x150Logo.png" Square44x44Logo="Assets\Square44x44Logo.png">
        <uap:DefaultTile Wide310x150Logo="Assets\Wide310x150Logo.png" Square71x71Logo="Assets\SmallTile.png" Square310x310Logo="Assets\LargeTile.png"/>
        <uap:SplashScreen Image="Assets\SplashScreen.png" />
        <uap:LockScreen BadgeLogo="Assets\BadgeLogo.png" Notification="badge"/>
      </uap:VisualElements>
      <Extensions>
        <uap:Extension Category="windows.appService" EntryPoint="WindowsAppService.AppService">
          <uap:AppService Name="XXXXXXXX.UWP.IPC" uap4:SupportsMultipleInstances="false" />
        </uap:Extension>
      </Extensions>
    </Application>
  </Applications>
  <!-- To host the BgTaskComponent, you must add this activatable class entry -->
  <Extensions>
    <Extension Category="windows.activatableClass.inProcessServer">
      <InProcessServer>
        <Path>WinRT.Host.dll</Path>
        <ActivatableClass ActivatableClassId="AppService-RuntimeComponent.AppService" ThreadingModel="both"/>
      </InProcessServer>
    </Extension>
  </Extensions>
  <Capabilities>
    <rescap:Capability Name="runFullTrust" />
    <Capability Name="internetClient" />
    <DeviceCapability Name="radios" />
    <DeviceCapability Name="bluetooth"/>
    <DeviceCapability Name="location"/>
    <DeviceCapability Name="serialcommunication">
      <Device Id="any">
        <Function Type="name:serialPort"/>
      </Device>
    </DeviceCapability>
  </Capabilities>
</Package>

补充排查信息 #

Edit 1：我制作了一个最小可复现的示例项目，里面的AppService在VS Release模式直接部署时能正常工作，但打包成MSIX安装后就会触发AppUnavailable。

Edit 2：我把调试器附加到backgroundTaskHost.exe上，当客户端调用AppServiceConnection.openAsync()时，抛出了如下异常：

Exception thrown at 0x00007FF984637F9A (KernelBase.dll) in backgroundTaskHost.exe: WinRT originate error - 0x80070002 : 'The system cannot find the file specified.'

有没有朋友能帮忙分析下，VS直接部署和MSIX安装后到底存在什么差异，导致AppService无法正常工作呢？

内容来源于stack exchange