azure-search-documents ContentUnderstandingSkill is missing model_name and model_deployment

[pamelafox]

• Package Name: azure-search-documents
• Package Version: 12.1.0b1
• Operating System: macOS 26.6.1 (arm64)
• Python Version: 3.13.13

Describe the bug

The ContentUnderstandingSkill model does not expose the model_name and model_deployment properties that correspond to the Azure AI Search 2026-05-01-preview REST properties modelName and modelDeployment.

These properties enable AI-generated descriptions for document-embedded images, charts, and diagrams. The package defaults to 2026-05-01-preview, and the same release includes the preview semantic chunking additions, but the Python model cannot represent the image-description configuration.

Service documentation: https://learn.microsoft.com/azure/search/cognitive-search-skill-content-understanding#skill-parameters

To Reproduce

1. Install azure-search-documents==12.1.0b1.
2. Run:

from azure.search.documents.indexes.models import ContentUnderstandingSkill

ContentUnderstandingSkill(
    name="content-understanding",
    description="Extract content and describe figures",
    context="/document",
    inputs=[],
    outputs=[],
    model_name="gpt-5.4",
    model_deployment="gpt-5.4",
)

The constructor fails with:

TypeError: ContentUnderstandingSkill.__init__() got an unexpected keyword argument 'model_name'

model_deployment is likewise absent from the generated model.

Expected behavior

ContentUnderstandingSkill should expose:

model_name: str | None
model_deployment: str | None

and serialize them as:

{
  "modelName": "gpt-5.4",
  "modelDeployment": "gpt-5.4"
}

The service requires both properties to be supplied together.

Screenshots

N/A

Additional context

The current workaround is to create or update the skillset with a raw 2026-05-01-preview REST payload through an authenticated SDK client send_request call. That works but loses the validation, discoverability, and type safety provided by the generated model.