Microsoft.VisualStudio.Composition.PartDiscoveryException: Failure while scanning type "Microsoft.VisualStudio.Copilot.Roslyn.Completion.AbstractBlueprintProvider....

Describe the issue

1.Medium Priority.
2.Regression issue: not repro in the Pre-release builds: C# Dev Kit Extension v3.29.214 & C# Extension v2.149.33 with the same environment.

It shows multiple exceptions in the C# Output when loading the project.

2026-09-16 09:04:55.601 [info] fail: Microsoft.CodeAnalysis.Remote.ExportProviderBuilder[0]
2026-09-16 09:04:55.601 [info] Encountered exception in the MEF composition
2026-09-16 09:04:55.602 [info] Microsoft.VisualStudio.Composition.PartDiscoveryException: Failure while scanning type "Microsoft.VisualStudio.Copilot.Roslyn.Completion.AbstractBlueprintProvider`1+DocumentCacheEntry".
2026-09-16 09:04:55.602 [info] ---> System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.CodeAnalysis.ExternalAccess.Copilot, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. The system cannot find the file specified.
2026-09-16 09:04:55.602 [info] File name: 'Microsoft.CodeAnalysis.ExternalAccess.Copilot, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'

Collect logs

csdevkit-logs-2026-09-16T01-31-30.zip

Steps to reproduce

1.Create a C# Console App and obeserve the C# Output .

Expected behavior

No error messages when loading the project.

Environment information

.NET Install Tool: 3.1.0
C# Dev Kit Extension: Release v3.40.202
C# Extension: main v2.152.19
.NET SDKs: 11.0.100-rc.1.26425.128
VSCode Stable: 1.138.0
Platform: Windows X64