Offline VSIX omits Roslyn Copilot and VSWebAssemblyBridge dependencies

[ghbugfinder]

Environment data

dotnet --info output:
.NET SDK:
Version: 10.0.400
Commit: 14fbf8d527
Workload version: 10.0.400-manifests.330ea142
MSBuild version: 18.9.6+14fbf8d52

Laufzeitumgebung:
OS Name: Windows
OS Version: 10.0.19045
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\10.0.400\

Installierte .NET-Workloads:
Es sind keine installierten Workloads zum Anzeigen vorhanden.
Für die Verwendung von workload sets bei der Installation neuer Manifeste konfiguriert.
Es sind keine Workloadsätze installiert. Führen Sie „dotnet workload restore“ aus, um einen Workloadsatz zu installieren.

Host:
Version: 10.0.11
Architecture: x64
Commit: e2f47b0110

.NET SDKs installed:
10.0.400 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 10.0.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 10.0.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 10.0.11 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
None

Environment variables:
Not set

global.json file:
Not found

Learn more:
https://aka.ms/dotnet/info

Download .NET:
https://aka.ms/dotnet/download
VS Code version: Tested with 1.134 win32-x64 zip version
C# Extension version: ms-dotnettools.csharp-2.140.9-win32-x64.vsix

C# logs

C# output window contents:

2026-08-21 21:11:09.376 [info] Installing C# dependencies...
2026-08-21 21:11:09.376 [info]

2026-08-21 21:11:09.376 [info] Platform: win32, x86_64

2026-08-21 21:11:09.376 [info]

2026-08-21 21:11:09.376 [info] Downloading package 'Language server for Roslyn Copilot integration'
2026-08-21 21:11:09.838 [info] Failed at stage: downloadPackage

2026-08-21 21:11:09.839 [info] Error: getaddrinfo ENOTFOUND roslyn.blob.core.windows.net

2026-08-21 21:11:09.839 [info]

2026-08-21 21:11:09.895 [info] Downloading package 'VSWebAssemblyBridge (Platform Agnostic)'
2026-08-21 21:11:09.942 [info] Failed at stage: downloadPackage

2026-08-21 21:11:09.942 [info] Error: getaddrinfo ENOTFOUND vsdebugger.blob.core.windows.net

2026-08-21 21:11:09.942 [info]

2026-08-21 21:11:09.960 [info] C# Extension activated in limited mode due to workspace trust not being granted.

Steps to reproduce

Follow https://github.com/dotnet/vscode-csharp/tree/main/docs/Installing-without-Internet-connectivity.md commit f76cda2 (exception: newest dotnet-sdk 10 used)

0. You'll have the same issue with the Mac and probably with the Linux version (being dependend on other platform agnostic downloads), but following I only documented the issue with the Windows x64 VSIX, so you would have to use other download links.
1. Use a "clean" Windows system (no dotnet core, VS Code ever installed and no roaming profiles) - you probably simply could download the VSIX, uninstall vscode-csharp, disconnect network, restart VS Code and try to reinstall, but these are the steps done with a clean Windows system
2. Install dotnet sdk 10.0.400 https://builds.dotnet.microsoft.com/dotnet/Sdk/10.0.400/dotnet-sdk-10.0.400-win-x64.exe
3. Download VSCode-win32-x64-1.134.0 in the zip version https://vscode.download.prss.microsoft.com/dbazure/download/stable/110a328ea54b42367b803ec53ee0bf52ef26b419/VSCode-win32-x64-1.134.0.zip
4. Unpack it and search in the extension window for C#, C# Dev Kit and .NET Install Tool and use the right mouse click to download the VSIX for Windows 64 bit
5. You should now have ms-dotnettools.csharp-2.140.9-win32-x64.vsix, ms-dotnettools.csdevkit-3.20.199-win32-x64.vsix, ms-dotnettools.vscode-dotnet-runtime-3.1.0.vsix.
6. Disconnect network and restart VSCode
7. Drag the downloaded VSIX one after the other (.NET Install Tool, C#, C# Dev Kit) into the extension window to install them and let the install procedure finish before moving ahead to the next VSIX.
8. Try to create a new .Net Project (template: Console app) still without internet connection.
9. As .vscode\extensions\ms-dotnettools.csharp-2.140.9 has an empty .roslynCopilot and .vswebassemblybridge folder it won't work, because the dependencies are missing.

Expected behavior

The VSIX should contain the obviously necessary runtime dependencies for "Language Server for Roslyn Copilot integration" in .roslynCopilot and "VSWebAssemblyBridge (Platform Agnostic)" in .vswebassemblybridge out of the box (or depend on another pre-downloadable VSIX for them) to be able to install without internet connectivity or it should be documented how to precache the downloaded zip files, so that the VSIX can find them locally and install them without internet connectivity.

Actual behavior

.roslynCopilot and .vswebassemblybridge are empty and according to package.json the packages seems to depend on internet connectivity for the download of https://roslyn.blob.core.windows.net/releases/Microsoft.VisualStudio.Copilot.Roslyn.LanguageServer-18.3.72-alpha.zip
and
https://vsdebugger.blob.core.windows.net/vswebassemblybridge-9-0-705702/vswebassemblybridge.zip