Mixins created from `obj.constructor` cannot have members

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### 🔎 Search Terms

mixin constructor property instance

### 🕗 Version & Regression Information

- This is the behavior in every version I tried, and I reviewed the FAQ for entries about mixins

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.3#code/C4TwDgpgBAwg9gOwM7AE4FcDGw6oDwAqAfFALxQIQDuAFAHQMCGqA5kgFxSMIgDaAugEoyJAgG4AUBMwAbRkiRQAYnDhQA3hKhQA9DqgB1XAGsuqOOgQATKAAtgwMBz0sAlsFvoARnUxwAtjr+rpjmSHAAZsA6BOAQAMqhrmDRrgroEEg6AMwAHAAsAIxaUFYQsszQvABEfshoWDio1fyc8PUY2Lh4HmlEkgC+UhGW2K6IUACyrgAergiFhFAQM8AQ1ortKJ1NeCpwREQ0SOiQqBUKnATCmtp6UADyANIlqBDA6KgIUBeKK2sbKAnM6-DQlbQRVQRGg3IbaAaDYajYDjb7TOYIABMS3+6ysin2RzgXgAVlcbiV7jA5AooAByGgAQQQiBA-gsil+gjpUHmflQb2wMhAy1WeMUXnk0FBdIIdLolP09KZLJ47PQnJpSG5vMU8iQrhYCEYXhk0BwUA80sQ20Y82AUEilri9LlABooF50A7ZTy-OgZDYvNB5ihuCjGGsbFR3LYuKVXBEIhA3ggHScvKBII6Ij8bWg7Wn6ft5a93p9vqDcYDiSTfPmdrgwdoIVCYRo4VAERIhkA

### 💻 Code

```ts
type Constructor = new(...args: any[]) => T;

class Foo {
// Work around https://github.com/microsoft/TypeScript/issues/3841
declare ["constructor"]: Constructor;
}

function Mixin1>(superclass: T) {
// OK
return class extends superclass {
foof() {}
};
}

function Mixin2(obj: T) {
// Class '(Anonymous class)' incorrectly extends base class 'T'.
// '(Anonymous class)' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'Foo'.
return class extends obj.constructor {
foof() {}
};
}
```

### 🙁 Actual behavior

`Mixin1` compiles fine, but `Mixin2` has an error:

```
Class '(Anonymous class)' incorrectly extends base class 'T'.
'(Anonymous class)' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'Foo'.
```

Removing the `foof` member causes it to compile without error.

### 🙂 Expected behavior

Both should compile fine because they are doing the same thing.

### Additional information about the issue

_No response_

Start by running the linked TypeScript Playground reproduction and compare Mixin1 with Mixin2, focusing on the class heritage expression using obj.constructor. The issue is done when Mixin2 can retain its foof member without the reported inheritance error while Mixin1 continues to compile.

Written by the indexing model from the issue text.