[BUG] OpenAPI Normalizer - Unnecessary allOf wrapping for oneOf/anyOf items with discriminator labels

[lucy66hw]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

The OpenAPINormalizer wraps oneOf and anyOf items into allOf compositions when they have discriminator labels (e.g., title field).

openapi-generator version

OpenAPI declaration file content or url

Pet:
  oneOf:
    - title: dog  
      description: "A dog pet"
      $ref: '#/components/schemas/Dog'
    - title: cat  
      description: "A cat pet"
      $ref: '#/components/schemas/Cat'
    - title: bird  
      description: "A bird pet"
      $ref: '#/components/schemas/Bird'

Actual:

Pet:
  oneOf:
    - allOf:  
        - $ref: '#/components/schemas/Dog'
      title: dog
      description: "A dog pet"
    - allOf:  
        - $ref: '#/components/schemas/Cat'
      title: cat
      description: "A cat pet"
    - allOf:  
        - $ref: '#/components/schemas/Bird'
      title: bird
      description: "A bird pet"
  discriminator:
    propertyName: petType

expected. For oneOf/anyOf discriminator labels, we should leave them unchanged.

Pet:
  oneOf:
    - title: dog 
      description: "A dog pet"
      $ref: '#/components/schemas/Dog'
    - title: cat  
      description: "A cat pet"
      $ref: '#/components/schemas/Cat'
    - title: bird  
      description: "A bird pet"
      $ref: '#/components/schemas/Bird'
  discriminator:
    propertyName: petType

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

Implement context-aware normalization. skip normalization for oneOf/anyOf items, but keep normalizing regular properties.