[http-client-csharp] AddTypeToKeep stores stale FQN after visitor namespace changes, causing public models to be internalized

[haiyuazhang]

Bug Report

Description

AddTypeToKeep(TypeProvider) eagerly resolves type.Type.FullyQualifiedName to a string at call time. When a visitor (e.g. NamespaceVisitor) later changes the type's namespace, the stored FQN becomes stale. PostProcessor.ShouldKeepType() then fails to match the type, causing it to be internalized even though @@access(public) was set.

This was discovered during the ProviderHub management SDK migration, where models like ManifestLevelPropertyBag and ProviderFeaturesRule were silently internalized despite explicit @@access(Access.public) decorators.

Root Cause

In CodeModelGenerator.cs:

public void AddTypeToKeep(TypeProvider type, bool isRoot = true)
    => AddTypeToKeep(type.Type.FullyQualifiedName, isRoot);

This is called from ModelProvider constructor (for Access == "public") and TypeFactory (for public enums) — both run before visitors execute.

The pipeline order in CSharpGen.ExecuteAsync():

1. Build TypeProviders (constructors run → AddTypeToKeep stores pre-visitor FQN)
2. Run visitors (NamespaceVisitor changes namespace → FQN changes)
3. Write generated files
4. PostProcessAsync() → PostProcessor receives stale FQNs in typesToKeep

In PostProcessor.ShouldKeepType(), both checks fail:

• Simple name "MyModel" vs typesToKeep containing "OldNamespace.MyModel" → no match
• Roslyn FQN "NewNamespace.Models.MyModel" vs "OldNamespace.MyModel" → no match

Impact

Models with @@access(public) get silently internalized when model-namespace is true (the mgmt default). This affects management SDK migrations where models like ManifestLevelPropertyBag (ProviderHub service) become internal despite explicit public access decorators.

Reproduction

[Test]
public void PublicModelTypeToKeepUpdatesAfterNamespaceChange()
{
    var inputModel = InputFactory.Model(
        "MockInputModel",
        access: "public");

    MockHelpers.LoadMockGenerator(
        inputModelTypes: [inputModel]);

    var modelProvider = CodeModelGenerator.Instance.OutputLibrary.TypeProviders
        .SingleOrDefault(t => t.Name == "MockInputModel") as ModelProvider;
    Assert.IsNotNull(modelProvider);

    var originalFqn = modelProvider!.Type.FullyQualifiedName;
    Assert.AreEqual("Sample.Models.MockInputModel", originalFqn);

    // Simulate a visitor changing the namespace (e.g., NamespaceVisitor appending ".Models")
    modelProvider.Update(@namespace: "NewNamespace.Models");
    var newFqn = modelProvider.Type.FullyQualifiedName;
    Assert.AreEqual("NewNamespace.Models.MockInputModel", newFqn);

    // After namespace change, the resolved root types should contain the updated FQN
    // so that PostProcessor.ShouldKeepType can match it against the generated code.
    var rootTypes = CodeModelGenerator.Instance.AdditionalRootTypes;
    Assert.IsTrue(rootTypes.Contains(newFqn),
        $"AdditionalRootTypes should contain the post-visitor FQN '{newFqn}' "
        + $"but only contains: [{string.Join(", ", rootTypes)}]");
}

Proposed Fix

Store TypeProvider references instead of eagerly resolving FQNs. Resolve lazily when AdditionalRootTypes/NonRootTypes are accessed (after visitors have run).