Spreading record on derived models doesn't validate compatibility with parent model

Considering we have spread overriding in model inheritance, I'd like to confirm how to interpret the additional property information for model `B` here:
- A: Does that mean union of `string | int32` ? Model B could accept both additional properties.
- B: Does that mean `int32` to override `string`? Model B could only accept int32 properties.

[playground](https://cadlplayground.z22.web.core.windows.net/?c=bW9kZWwgQSB7DQogIC4uLlJlY29yZDxzdHJpbmc%2BOw0KfQ0KDQrGJkIgZXh0ZW5kc9IwaW50MzLHLw%3D%3D&e=%40typespec%2Fopenapi3&options=%7B%7D)

```ts
model A {
...Record;
}

model B extends A {
...Record;
}
```