[ContentUnderstanding] RecordMergePatchUpdate leaks as public model name

[yungshinlintw]

Bug: RecordMergePatchUpdate leaks as public model name in Python SDK

Package

azure-ai-contentunderstanding

Description

The Python SDK exposes RecordMergePatchUpdate as a public model in azure.ai.contentunderstanding.models. This is a synthetic type generated by the TypeSpec Python emitter from MergePatchUpdate<ContentUnderstandingDefaults> — it has no meaningful semantics and should not be part of the public API.

Root Cause

The TypeSpec route definition uses:

updateDefaults is Foundations.Operation<
    MergePatchUpdate<ContentUnderstandingDefaults>,
    ContentUnderstandingDefaults,
    ServiceTraits
>;

ContentUnderstandingDefaults has a single field modelDeployments: Record<string>. The Python emitter generates a synthetic model RecordMergePatchUpdate for the merge-patch body type, which is effectively just Dict[str, str].

What the user sees

1. In models/__init__.py: RecordMergePatchUpdate is exported as a public type
2. In method signatures (generated _operations.py):

   def update_defaults(
       self,
       *,
       model_deployments: Optional[RecordMergePatchUpdate] = None,
       ...
   )

3. In docstrings: :paramtype model_deployments: ~azure.ai.contentunderstanding.models.RecordMergePatchUpdate
4. In _models.py: An empty class with no fields:

   class RecordMergePatchUpdate(_Model):
       """RecordMergePatchUpdate."""

Current Workaround

In models/_patch.py, we alias it to Dict[str, str]:

RecordMergePatchUpdate = Dict[str, str]

This makes it work at runtime, but the name still appears in IDE tooltips, documentation, and APIView.

Expected Behavior

The emitter should resolve MergePatchUpdate<T> where T has a single Record<string> field to Dict[str, str] directly, rather than generating a synthetic model class. At minimum, the generated method signatures should use Dict[str, str] instead of RecordMergePatchUpdate.

Affected Files (generated)

• azure/ai/contentunderstanding/_operations/_operations.py — sync method signatures and docstrings
• azure/ai/contentunderstanding/aio/_operations/_operations.py — async method signatures and docstrings
• azure/ai/contentunderstanding/models/_models.py — empty model class definition

Environment

• TypeSpec commit: 2b2d493e2e883fcf474b3554839d97d1b5be1604
• Repo: Azure/azure-sdk-for-python, branch cu_sdk/ga
• PR: Content Understanding GA SDK for Python #45092