Upgrade Agent misses prerelease Visual Studio instances and falsely reports WebApplication tooling missing

Summary

Upgrade Agent reported that Visual Studio, the Web Application workload, .NET Framework targeting support, and Microsoft.WebApplication.targets were missing.

The machine had multiple complete prerelease Visual Studio installations with MSBuild and Microsoft.WebApplication.targets available.

Observed with: Upgrade Agent 1.1.404, GitHub Copilot App 1.1.10, Windows

Reproduction

1. Install a prerelease Visual Studio instance, such as Insiders or Preview, with ASP.NET/Web Application build support.
2. Run Upgrade Agent against a legacy ASP.NET Framework Web Application Project.
   • Example repo to use: ContosoUniversity source: https://github.com/Azure-Samples/dotnet-migration-copilot-samples/tree/main/ContosoUniversity
3. Ask it to assess baseline restore and build viability.

Actual result

Upgrade Agent:

• did not discover the prerelease Visual Studio instances
• used the .NET SDK’s bundled MSBuild
• failed with MSB4019 for missing Microsoft.WebApplication.targets
• classified the failure as an environment/setup blocker
• recommended installing tooling that was already present

Expected result

Upgrade Agent should:

1. Discover stable and prerelease Visual Studio instances.
2. Inspect each instance for MSBuild, required workloads, targeting packs, and target files.
3. Select the newest complete compatible installation.
4. Report missing tooling only after checking all eligible instances.

For example, vswhere requires -prerelease to include prerelease installations:

vswhere.exe -all -products * -prerelease