abstract type guard does not narrow when keyed with a unique symbol

### 🔎 Search Terms

abstract type guard symbol

### 🕗 Version & Regression Information

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

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250810&ssl=28&ssc=2&pln=1&pc=1#code/FAYw9gdgzgLgBASygIQIYCc4F44GUCeAtgEZgA2AFAERJrpUCUA3MMKsbOqiPCGalChwAYmDBwA3sDgy47Tt3i0MFBgC44MABZJEQui1lyOMLjzgBtZegC6qjdt26DrI4QCm2sABN7cAG5gCN6S0kayCABmcBSOUFYoGHYMDKHh6XAA9JlwACo6QlBaYACuZCEQYPDE7nIQcO7o6GDoYRmycQB0xBgAsp7Fvsxt4QC+DWRQtVExXdaqqVLtRl096P1eQ4YZoyO7u6D8gnB0DQAeMO4Q3kKi4kuyYP6N6MHTieh+cXonGGkZ6E8JXQ9VMJXc2xkByMTxeb0s1mSDgKP1OD3SgJgwNB6HBkLg0Nkaw2gz8gWCkn2QA

### 💻 Code

```ts
const isBar = Symbol("isBar");

abstract class Foo {
abstract isBar(): this is Bar;
abstract [isBar](): this is Bar;

method(): void {
if (this[isBar]()) {
// This should not be an error, it should work the same as .isBar()
this.barMethod();
} else if (this.isBar()) {
this.barMethod();
}
}
}

class Bar extends Foo {
override isBar(): this is Bar {
return true;
}

override [isBar](): this is Bar {
return true;
}

barMethod(): void {}
}
```

### 🙁 Actual behavior

TS reports an error:

> `Property 'barMethod' does not exist on type 'Foo'. Did you mean 'method'?(2551)`

### 🙂 Expected behavior

No error should happen here, the type guard should work the same as the non-symbol version of the method.

### Additional information about the issue

_No response_

Commencez par le TypeScript Playground lié et reproduisez la différence entre l’appel unique-symbol et l’appel nommé isBar() dans Foo.method(). Suivez le comportement du rétrécissement de type pour les deux gardes de type abstraits, puis vérifiez que l’appel utilisant une clé symbolique réduit this à Bar et ne signale plus l’erreur barMethod.

Rédigé par le modèle d'indexation à partir du texte de l'issue.