Visual Studio VSIX Package Not Loading in Experimental Instance (`/rootsuffix Exp`)

Summary

A previously working VSIX extension no longer loads in the Visual Studio Experimental Instance.

• The .vsix package builds and installs successfully.
• InitializeAsync() on the AsyncPackage is never called.
• No ActivityLog.xml is generated.
• All package registration appears correct (.pkgdef, .vsixmanifest, GUID, etc.).
• No error in the Output window — only the generic “package did not load” warning.

Development Environment

• Visual Studio 2022 Community (v17.x, latest updates applied)
• Target Framework: .NET Framework 4.8
• VS SDK Packages:
  • Microsoft.VisualStudio.SDK version 17.0.32112.339
  • Microsoft.VSSDK.BuildTools version 17.13.2126
• Launch command:

devenv.exe /rootsuffix Exp /log

Project Structure

• Standard VSIX containing:
• AsyncPackage-derived class
• [ProvideAutoLoad], [ProvideMenuResource] attributes
• Proper source.extension.vsixmanifest, .pkgdef, .resx, .vsct, .bmp/.png assets
• All GUIDs and namespaces are aligned
• Output includes:
• FolderCsFileOpener.dll
• FolderCsFileOpener.pkgdef
• source.extension.vsixmanifest

Issue Description

Despite successful build and installation:

• FolderCsFileOpenerPackage.InitializeAsync() is never triggered
• ActivityLog.xml is not generated, even with /log
• Menu commands do not appear
• It appears that the extension is completely skipped during Visual Studio load

.pkgdef content sample:

[$RootKey$\Packages\{c9c3d4e5-384e-447a-9791-eb2d8649b7fe}]

@="FolderCsFileOpenerPackage"

"InprocServer32"="$WinDir$\SYSTEM32\MSCOREE.DLL"

"Class"="FolderCsFileOpener.FolderCsFileOpenerPackage"

"Assembly"="FolderCsFileOpener, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"

"AllowsBackgroundLoad"=dword:00000001

What Has Been Verified

GUIDs match between .pkgdef, .vsixmanifest, and AsyncPackage class

InitializeAsync() includes Debug.WriteLine logging, but they are never executed

.dll file contains correct class (confirmed via ILSpy)

AssemblyInfo.cs and metadata are aligned

All local caches were deleted (bin/, obj/, %LocalAppData%\Microsoft\VisualStudio\17.0_Exp)

Reinstalled and repaired Visual Studio — no improvement

Copied code to fresh project → same result

Suspected Root Causes

• Visual Studio skips loading the package at startup
• Exp instance registry or state corruption
• ProvideAutoLoad silently failing due to internal change or misregistration
• ActivityLog.xml fails to initialize due to deeper initialization error
• Possibly caused by a recent Visual Studio update
• GitHub source for reproducible issue: 🔗 https://github.com/srtdog64/FolderCsFileOpener/tree/master

Request for Help

Is there any way to force-load the extension or trace why it's being skipped silently?

Can Microsoft confirm if recent versions of Visual Studio introduced changes that affect VSIX auto-loading, ProvideAutoLoad, or experimental instance behavior?

Are there known cases where ActivityLog.xml is not generated even with /log, or the package system is partially disabled?