Model Composition with ‘allOf’ Is Missing Fields

Describe the bug
Using a composition model (https://spec.openapis.org/oas/v3.0.4.html#models-with-composition) does not generate the target type but only the underlying type. For a type A which consists of the fields of B and some additional fields, only B is generated. Furthermore, A is replaced by B.

The spec below generates the following function:

def sync_detailed(
    *,
    client: AuthenticatedClient | Client,
    body: Base,
) -> Response[Any]: ...

I would expect that the model Network is generated and used instead of Base. The Network model should include the field of Base and the field non_base_field.

OpenAPI Spec File

openapi: 3.0.0
info:
  title: Service
  version: 0.0.0
paths:
  /widgets:
    get:
      responses:
        "200":
          description: The request has succeeded.
          content:
            application/json:
              schema:
                nullable: true
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/Network"
components:
  schemas:
    Base:
      type: object
      required:
        - base_field
      properties:
        base_field:
          type: string
    Network:
      type: object
      required:
        - non_base_field
      properties:
        non_base_field:
          type: string
      allOf:
        - $ref: "#/components/schemas/Base"

Desktop (please complete the following information):

• OS: Linux
• Python Version: 3.13.11
• openapi-python-client version: 0.28.1

Additional context
Add any other context about the problem here.

Bắt đầu bằng cách chạy đặc tả OpenAPI được cung cấp và so sánh các model Network và Base được tạo ra cùng với signature của sync_detailed. Truy vết cách các schema allOf được xử lý trong quá trình tạo model và endpoint. Công việc được xem là hoàn tất khi Network được tạo với cả hai field, endpoint sử dụng Network thay vì Base và một regression test bao quát composition này.