Adding a new optional property to the request/response body is considered backward incompatible.

Hi,
Why adding a new optional property (with default value) is considered to be an incompatible change?

• V1 client sends a request without a new field - then the default value will be used by the V2 server - [OK]
• V1 client receives the response from the V2 server with a new field - it will simply be ignored by the V1 client - [OK]

I really do not see why the diff tool reports it as an incompatible change?

首先，使用两个最小化的 OpenAPI 规范复现兼容性报告：一个包含原始请求/响应体，另一个添加一个带有默认值的可选属性。跟踪 diff 工具如何对该请求和响应变更进行分类，然后根据 issue 中描述的预期向后兼容行为确认结果。