Find a Solution to Handling External Metadata References

[jorgerangel-msft]

In libraries like Storage and Communication, some custom ctors reference types from external libraries that are not added as metadata references in the generator which leads to types like global::.StorageSharedKeyCredential credential. We should explore a good way of handling this possibly via a new central plugin?

[jorgerangel-msft]

One possible avenue is using a new clientOption via tsp:

@clientOption("additionalMetadataReference", "Azure.Storage.Common")

Then in the generator we try adding the reference by looking at nuget cache

[JoshLove-msft]

The custom code Roslyn workspace is created with only framework assemblies. When user code references types from
external NuGet packages (e.g., Azure.Storage.Common.StorageSharedKeyCredential), those assemblies aren't available
as metadata references.

Most Natural Solution: Parse .csproj PackageReferences

The generator already has all the pieces — they just need to be connected:

1. .csproj parsing — GeneratedCodeWorkspace.LoadBaselineContract() already opens the .csproj via
   ProjectRootElement.Open() but only reads one property. Extend it to also extract PackageReference items.
2. NuGet resolution — NugetPackageDownloader already implements full NuGet package download/cache logic but is only
   used for baseline contracts.
3. Adding references — CodeModelGenerator.AddMetadataReference() exists as the public API.

The flow would be:

Generator startup
→ Read .csproj PackageReference items
→ For each, resolve assemblies from NuGet global cache (~/.nuget/packages/)
→ Add as metadata references via AddMetadataReference()
→ Custom code workspace now compiles correctly

This requires no TypeSpec decorator changes — it works automatically for any project that already has the right
PackageReference entries in its .csproj (which Storage and Communication already do).