[main] Source-build legs fail with CS8032 loading ASP.NET Core analyzers #5674

Source-build legs in run 20261020.4 fail while building src/sdk/src/Dotnet.Watch/Watch/Microsoft.DotNet.HotReload.Watch.csproj.

The compiler reports CS8032 when loading analyzers from Microsoft.AspNetCore.App.Ref/12.0.0-alpha.1.26520.104:

CSC : error CS8032: An instance of analyzer
Microsoft.AspNetCore.Analyzers.Kestrel.ListenOnIPv6AnyAnalyzer
cannot be created from .../analyzers/dotnet/cs/Microsoft.AspNetCore.App.Analyzers.dll :
System.IO.FileNotFoundException: Could not load file or assembly
'System.Collections.Immutable, Version=12.0.0.0, Culture=neutral,
PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.

Similar errors are reported for other analyzers in Microsoft.AspNetCore.App.Analyzers.dll and Microsoft.Extensions.Validation.ValidationsGenerator.dll.

All nine source-build legs fail with this symptom, including online and offline builds and builds using either the Microsoft SDK or the previously source-built SDK.

Example failing step

The same error also appears in run 20261019.28, with Microsoft.AspNetCore.App.Ref/12.0.0-alpha.1.26519.128.