Make bundled SDK feature package versions discoverable by Dependabot

Directory.Packages.props

@@ -12,6 +12,10 @@
     <CentralPackageTransitivePinningEnabled>false</CentralPackageTransitivePinningEnabled>
   </PropertyGroup>
   <PropertyGroup Label="Product dependencies">
+    <!-- AspireHostingTestingVersion is consumed by the build and baked into the shipped MSTest.Sdk
+         template. It MUST be kept in sync with the literal Aspire.Hosting.Testing PackageVersion
+         declared near the bottom of this file (the one Dependabot updates). The
+         _ValidateBundledSdkFeatureVersions target there fails the build if the two drift apart. -->
     <AspireHostingTestingVersion>13.2.1</AspireHostingTestingVersion>
     <MicrosoftBuildVersion>17.11.48</MicrosoftBuildVersion>
     <MicrosoftCodeAnalysisVersion>3.11.0</MicrosoftCodeAnalysisVersion>
@@ -27,6 +31,10 @@
     <MicrosoftNETCoreUniversalWindowsPlatformVersion>6.2.14</MicrosoftNETCoreUniversalWindowsPlatformVersion>
     <!-- Test Platform, .NET Test SDK and Object Model  -->
     <MicrosoftNETTestSdkVersion>18.4.0</MicrosoftNETTestSdkVersion>
+    <!-- MicrosoftPlaywrightVersion is consumed by the build and baked into the shipped MSTest.Sdk
+         template. It MUST be kept in sync with the literal Microsoft.Playwright.MSTest.v4
+         PackageVersion declared near the bottom of this file (the one Dependabot updates). The
+         _ValidateBundledSdkFeatureVersions target there fails the build if the two drift apart. -->
     <MicrosoftPlaywrightVersion>1.60.0</MicrosoftPlaywrightVersion>
     <MicrosoftTestingExtensionsFakesVersion>18.1.1</MicrosoftTestingExtensionsFakesVersion>
     <!-- Microsoft.Testing.Internal.Framework is an internal-only NuGet (consumed by tests that
@@ -122,10 +130,38 @@
     <PackageVersion Include="xunit.v3.mtp-v2" Version="3.2.2" />
   </ItemGroup>
   <!--
-    Declare below packages that we will be referenced through MSTest.Sdk but don't have direct reference.
-    This allows dependabot to suggest updates.
+    Declare below packages that are referenced through MSTest.Sdk but don't have a direct
+    PackageReference in this repo, so that Dependabot can discover and update them.
+
+    The version MUST be a literal here (not an MSBuild property such as
+    $(MicrosoftPlaywrightVersion)): Dependabot does not update a Central Package Management
+    PackageVersion whose Version is an MSBuild property interpolation when the package has no
+    direct PackageReference, so a property-based version silently stops receiving updates.
+    See dependabot/dependabot-core#5812 and dependabot/dependabot-core#7183.
+
+    Each literal version is duplicated as the matching *Version property (defined near the top of
+    this file) which is the value actually consumed by the build and baked into the MSTest.Sdk
+    template (see MSTest.Sdk.csproj). The two cannot be unified because the consuming property must
+    be a plain scalar (an item transform such as @(PackageVersion->...) stored in a property is not
+    expanded and breaks string concatenation, e.g. MSB4012), while Dependabot needs the literal on
+    the PackageVersion. The _ValidateBundledSdkFeatureVersions target below fails the build if the
+    property and the PackageVersion ever drift apart (e.g. after Dependabot bumps only the
+    PackageVersion), so the duplication can never ship out of sync.
     -->
   <ItemGroup Label="Declared by MSTest.Sdk but not used directly">
-    <PackageVersion Include="Microsoft.Playwright.MSTest.v4" Version="$(MicrosoftPlaywrightVersion)" />
+    <PackageVersion Include="Aspire.Hosting.Testing" Version="13.2.1" />
+    <PackageVersion Include="Microsoft.Playwright.MSTest.v4" Version="1.60.0" />
   </ItemGroup>
+  <Target Name="_ValidateBundledSdkFeatureVersions"
+          BeforeTargets="CollectPackageReferences;GenerateNuspec;Build;Pack"
+          Condition=" '$(MSBuildProjectName)' == 'MSTest.Sdk' ">
+    <PropertyGroup>
+      <_AspireHostingTestingPackageVersion>@(PackageVersion->WithMetadataValue('Identity', 'Aspire.Hosting.Testing')->'%(Version)')</_AspireHostingTestingPackageVersion>
+      <_MicrosoftPlaywrightPackageVersion>@(PackageVersion->WithMetadataValue('Identity', 'Microsoft.Playwright.MSTest.v4')->'%(Version)')</_MicrosoftPlaywrightPackageVersion>
+    </PropertyGroup>
+    <Error Condition=" '$(AspireHostingTestingVersion)' != '$(_AspireHostingTestingPackageVersion)' "
+           Text="AspireHostingTestingVersion ('$(AspireHostingTestingVersion)') is out of sync with the 'Aspire.Hosting.Testing' PackageVersion ('$(_AspireHostingTestingPackageVersion)') in Directory.Packages.props. Update the AspireHostingTestingVersion property to match (Dependabot only updates the PackageVersion)." />
+    <Error Condition=" '$(MicrosoftPlaywrightVersion)' != '$(_MicrosoftPlaywrightPackageVersion)' "
+           Text="MicrosoftPlaywrightVersion ('$(MicrosoftPlaywrightVersion)') is out of sync with the 'Microsoft.Playwright.MSTest.v4' PackageVersion ('$(_MicrosoftPlaywrightPackageVersion)') in Directory.Packages.props. Update the MicrosoftPlaywrightVersion property to match (Dependabot only updates the PackageVersion)." />
+  </Target>
 </Project>