[v5] PublishVSExtension fails when VS 2026 Enterprise is installed on the agent

[tomasherceg]

Additional context
I run the PublishVSExtension task on my own Windows agent, and since I installed the RTM version of Visual Studio 2026 on the agent, the task fails with this exception:

2025-11-17T10:00:40.8195931Z ##[section]Starting: Publish Visual Studio Extension
2025-11-17T10:00:40.8422015Z ==============================================================================
2025-11-17T10:00:40.8422347Z Task         : Publish Visual Studio Extension
2025-11-17T10:00:40.8422535Z Description  : Publish Visual Studio extension to the Visual Studio Marketplace
2025-11-17T10:00:40.8422789Z Version      : 5.0.541
2025-11-17T10:00:40.8422938Z Author       : Microsoft Corporation
2025-11-17T10:00:40.8423746Z Help         : [More Information](https://marketplace.visualstudio.com/items?itemName=ms-devlabs.vsts-developer-tools-build-tasks)
2025-11-17T10:00:40.8424136Z ==============================================================================
2025-11-17T10:00:41.3857369Z Logging in as 'xxxxx'
2025-11-17T10:00:41.5502870Z [command]"C:\Program Files\Microsoft Visual Studio\18\Enterprise\VSSDK\VisualStudioIntegration\Tools\Bin\VsixPublisher.exe" login -personalAccessToken *** -publisherName xxxxx
2025-11-17T10:00:43.3369073Z VSSDK: error VsixPub0031 : An error occurred while attempting to authenticate: Could not load file or assembly 'Microsoft.Identity.Client, Version=4.72.1.0, Culture=neutral, PublicKeyToken=0a613f4dd989e8ae' or one of its dependencies. The system cannot find the file specified.
2025-11-17T10:00:43.3396751Z ##[error]Login failed.
2025-11-17T10:00:43.3404342Z ##[error]Login failed.
2025-11-17T10:00:43.3406853Z Logging out publisher 'xxxxx'
2025-11-17T10:00:43.3407209Z Logout successful.
2025-11-17T10:00:43.3407485Z All done
2025-11-17T10:00:43.3532830Z ##[section]Finishing: Publish Visual Studio Extension

I am unsure if this is a problem with the Azure DevOps task or if there is an issue with VsixPublisher.exe, which is distributed with the latest version of Visual Studio.

[jessehouwing]

I suspect that it's a Visual Studio bug.

This can generally be fixed by adding/editing a VsixPublisher.exe.config and adding the correct probing paths or assembly binding redirects to allow it to load the assembly from a different path or from a different version.

I just repo'ed this locally on the CLI:

.\VsixPublisher.exe login -personalAccessToken *** -publisherName xxxxx
VSSDK: error VsixPub0031 : An error occurred while attempting to authenticate: Could not load file or assembly 'Microsoft.Identity.Client, Version=4.72.1.0, Culture=neutral, PublicKeyToken=0a613f4dd989e8ae' or one of its dependencies. The system cannot find the file specified.

haven't found the right probing path yet, but this is clearly a bug on the visual studio side.