build(desktop): install the pinned help into dev build output

Only the packaging scripts installed Help\, so F1 and the Help menu in a
dev build always said help was not installed. The build now downloads the
help.json release once into obj\ and copies it beside OpenNest.exe; CI and
publish output are unaffected.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest/OpenNest.csproj

@@ -62,4 +62,30 @@
       <LastGenOutput>Settings.Designer.cs</LastGenOutput>
     </None>
   </ItemGroup>
+
+  <!-- Dev builds get the help release pinned in scripts/help.json, downloaded once into obj/
+       and refreshed when the pin changes. Packaging scripts install help themselves; CI and
+       offline builds skip it (/p:InstallHelp=false), and a failed download only warns. -->
+  <PropertyGroup>
+    <InstallHelp Condition="'$(InstallHelp)' == '' and '$(CI)' == 'true'">false</InstallHelp>
+    <HelpPin>$(MSBuildProjectDirectory)\..\scripts\help.json</HelpPin>
+    <HelpCacheDir>$(MSBuildProjectDirectory)\$(BaseIntermediateOutputPath)help\</HelpCacheDir>
+    <HelpCacheStamp>$(MSBuildProjectDirectory)\$(BaseIntermediateOutputPath)help.stamp</HelpCacheStamp>
+  </PropertyGroup>
+
+  <Target Name="DownloadPinnedHelp" Condition="'$(InstallHelp)' != 'false' and '$(OS)' == 'Windows_NT'"
+          Inputs="$(HelpPin)" Outputs="$(HelpCacheStamp)">
+    <RemoveDir Directories="$(HelpCacheDir)" />
+    <Exec Command="powershell -NoProfile -ExecutionPolicy Bypass -File &quot;$(MSBuildProjectDirectory)\..\scripts\Install-Help.ps1&quot; -Destination &quot;$(HelpCacheDir.TrimEnd('\'))&quot;"
+          ContinueOnError="true" />
+    <Touch Files="$(HelpCacheStamp)" AlwaysCreate="true" Condition="Exists('$(HelpCacheDir)index.html')" />
+  </Target>
+
+  <Target Name="CopyPinnedHelp" AfterTargets="Build" DependsOnTargets="DownloadPinnedHelp"
+          Condition="'$(InstallHelp)' != 'false' and '$(OS)' == 'Windows_NT'">
+    <ItemGroup>
+      <HelpFile Include="$(HelpCacheDir)**\*" />
+    </ItemGroup>
+    <Copy SourceFiles="@(HelpFile)" DestinationFolder="$(OutDir)Help\%(RecursiveDir)" SkipUnchangedFiles="true" />
+  </Target>
 </Project>

docs/desktop-help.md

@@ -17,6 +17,10 @@ holds only the code that shows that HTML and the pin of which help release ships
 - The help folder is `Help\` beside `OpenNest.exe`. Set `OPENNEST_HELP_DIR` to a local
   opennest-help `site\` build to preview unreleased pages. Without either, the menu
   explains that help is not installed.
+- A Windows `dotnet build` of `OpenNest.csproj` downloads the pinned release once into
+  `obj\help\` (again when `scripts/help.json` changes) and copies it to the build output's
+  `Help\`. A failed download only warns. CI (`CI=true`) skips it; pass
+  `-p:InstallHelp=false` to skip it offline. It never reaches `dotnet publish` output.
 
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