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.

Beginne damit, die bereitgestellte OpenAPI-Spezifikation auszuführen und die generierten Network- und Base-Modelle sowie die Signatur von sync_detailed zu vergleichen. Verfolge, wie allOf-Schemas während der Generierung von Modellen und Endpunkten behandelt werden. Als abgeschlossen gilt die Aufgabe, wenn Network mit beiden Feldern generiert wird, der Endpunkt Network anstelle von Base verwendet und ein Regressionstest diese Komposition abdeckt.