OpenAPI Generator duplicates models when using OAS 3.1 $ref with sibling annotations

When using OpenAPI 3.1 with JSON Schema 2020-12 and external $defs, OpenAPI Generator generates duplicate C# models (e.g. HeightCharacteristic and HeightCharacteristic1) and incorrect documentation.

This occurs when:

• Multiple schemas reference the same $defs alias
• The $ref usage sites include different sibling annotations (e.g. description)
• The generator is run on a sufficiently large schema graph (e.g. DATEX II)

Although the schemas are valid JSON Schema 2020-12, OpenAPI Generator:

1. Incorrectly merges $ref sibling annotations into the resolved target schema and caches it without context.
2. Treats later traversals of the same canonical schema (with different merged annotations) as distinct schema identities, leading to *1 suffixed duplicate models.
3. Copies XML documentation from the first encountered context into later models (documentation bleed).

This is deterministic with large schemas in DATEX and not user error, below a reproducable example.

Using 7.17.x for NET CORE

Steps to reproduce:

java -jar openapi-generator-cli.jar generate -i repro.json -g aspnetcore -o out --additional-properties=aspnetCoreVersion=6.0 --skip-operation-example

Schema files:

repro.json

DATEXII_3_MessageContainer.json

DATEXII_3_Common.json

Observed result:

• Duplicate models generated (HeightCharacteristic, HeightCharacteristic1)
• XML documentation copied from the first-encountered context

Possible fixes:

• Treat $ref sibling annotations as usage-site only, not part of the resolved schema cache.
• Deduplicate models based on canonical schema identity, not merged/annotated instances.

Start by running the supplied openapi-generator-cli command with repro.json, then compare the generated HeightCharacteristic and HeightCharacteristic1 models and their XML documentation. Trace how the external $defs references and sibling descriptions are resolved and cached during generation. Done means the same canonical schema produces one C# model and usage-site documentation does not bleed between contexts.