diff --git a/Directory.Build.targets b/Directory.Build.targets
index b692ee649bce..6713b61f0524 100644
--- a/Directory.Build.targets
+++ b/Directory.Build.targets
@@ -3,7 +3,10 @@
   <Import Project="Sdk.targets" Sdk="Microsoft.DotNet.Arcade.Sdk" />
 
   <PropertyGroup>
-    <IsPackable Condition="$(TargetFramework.Contains('netstandard'))">false</IsPackable>
+    <!-- Don't ship .NET Standard packages by default, EXCEPT when a project explicitly opts in via
+         <IsPackable>true</IsPackable> (e.g. the workload manifest and SDK packs, which are netstandard-only
+         but must ship). The '$(IsPackable)' == '' guard preserves that explicit opt-in. -->
+    <IsPackable Condition="$(TargetFramework.Contains('netstandard')) and '$(IsPackable)' == ''">false</IsPackable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Workload/workloads.csproj b/src/Workload/workloads.csproj
index 5070c94398a3..5f4e8d4e9ed9 100644
--- a/src/Workload/workloads.csproj
+++ b/src/Workload/workloads.csproj
@@ -27,7 +27,14 @@
     <SwixTargetsPath>$(PkgMicroBuild_Plugins_SwixBuild_Dotnet)\build\MicroBuild.Plugins.SwixBuild.targets</SwixTargetsPath>
   </PropertyGroup>
 
-  <Import Project="$(WorkloadMsiGenProps)" />
+  <!--
+    vs-workload.props is generated by _GenerateVSWorkloadProps in Microsoft.NET.Sdk.Maui.Manifest.csproj
+    (AfterTargets="Build") during the manifest pack. The import is conditional on Exists(...) so that a
+    missing file does NOT fail at evaluation time with a cryptic MSB4019 that points at this line; instead
+    _EnsureWorkloadMsiGenProps (a dependency of the MSI-generation target below) fails fast at the point the
+    file is actually consumed, with an actionable message naming the root cause. When the file exists, this
+    import behaves exactly as before. -->
+  <Import Project="$(WorkloadMsiGenProps)" Condition="Exists('$(WorkloadMsiGenProps)')" />
 
     <!-- Provide default values for properties that can be set in vs-workload.props -->
   <PropertyGroup>
@@ -109,8 +116,20 @@
     <Message Text="Generated MSI version: %(WorkloadPackages.Filename) - %(WorkloadPackages.MsiVersion)" Importance="High" />
   </Target>
 
+  <!--
+    Fail fast (with an actionable, self-routing message) if vs-workload.props was not generated by the time
+    the workload MSIs are actually built. This is wired as a dependency of _GenerateAndSignMsis - the target
+    that consumes @(WorkloadPackages) from the props - so it only runs on the build/MSI path. Restore,
+    design-time builds, and unrelated target invocations never reach this target, so it does not break those.
+    A full Build of this project does require the props (that is by design - you cannot generate the MSIs
+    without it), so in that case the error is the intended, accurate failure rather than the cryptic MSB4019. -->
+  <Target Name="_EnsureWorkloadMsiGenProps">
+    <Error Condition="!Exists('$(WorkloadMsiGenProps)')"
+        Text="vs-workload.props was not generated ('$(WorkloadMsiGenProps)'). This usually means the workload manifest pack ran with IsPackable=false (the official 'Pack, Sign' step runs -pack without -build, so _GenerateVSWorkloadProps (AfterTargets=Build) in Microsoft.NET.Sdk.Maui.Manifest.csproj never ran). Ensure the netstandard IsPackable guard in Directory.Build.targets preserves the manifest pack's explicit &lt;IsPackable&gt;true&lt;/IsPackable&gt;. See PR #36089 / #36088." />
+  </Target>
+
   <Target Name="_GenerateAndSignMsis"
-      DependsOnTargets="_SetMsiVersionFromNuGetVersion;_CreateManifestMsiVersionsWithDateTime"
+      DependsOnTargets="_EnsureWorkloadMsiGenProps;_SetMsiVersionFromNuGetVersion;_CreateManifestMsiVersionsWithDateTime"
       BeforeTargets="SignFiles" >
     <CreateVisualStudioWorkload
         AllowMissingPacks="true"