Solutions and build configuration selection are broken when in mono-repository with multiple solutions

Describe the Issue

We have a mono-repository with a number of solutions located in subfolders. Right now there is no way to select solution and build configuration when opening from the repository root. Clicking on "C# Workspace Dev Mode" leads to the page instead of showing the list of solutions and configurations.

The commands ".Net: Select Configuration" and ".Net: Switch Solution" work and show available build configurations and solutions. But there is no way to do that via UI.

On top of that, selected Build configuration is not displayed anywhere in the bottom bar.

Reason that we don't want to put solutions in the root is that we have scoped agent rules, a plenty of projects, and we don't want to pollute the root repo folder. We also don't open specific app because we have an agentic harness and skills setup to account for the project structure.

Steps To Reproduce

1. Create the project with the following structure:

- repo root
    - apps
        - app A
            - proj1
            - proj2
            - proj3
            - appA.slnx
        - app B
            - appB.slnx

2. Open the project from repo root
3. No selector is available for solution:

Expected Behavior

Previous version was showing the available solutions even if they are located in subfolders as well as build configuration.

I expect that C# DevKit let's me choose the solution and debug configuration when I click on the button in the bottom bar.

DevKit console

2026-06-03 06:01:06.583 [info] Discovered Project System Host (PID 31718) for pshost.
2026-06-03 06:01:06.583 [info] Project System Host PID: 31718
2026-06-03 06:01:06.751 [info] Completed: collecting .csproj files in the workspace in C# Dev Kit server (23783ms)
2026-06-03 06:01:06.763 [info] Starting: Restoring NuGet packages
2026-06-03 06:01:06.763 [info] Selected configuration: <Default>, active configuration: Debug|Any CPU
2026-06-03 06:01:06.763 [info] Completed: Opening a solution (23795ms)

Environment Information

• Os: MacOs 26.5.1
• VS Code: 1.122.1
• DevKit: 3.20.199

Reproduce the issue with multiple .slnx files in subfolders opened from the repository root. Start by comparing the working ".Net: Select Configuration" and ".Net: Switch Solution" commands with the C# Dev Kit bottom-bar UI and the DevKit console output. Done means the UI lists available solutions and configurations and displays the selected build configuration.