False-positive `unintentional comparison` error with closures

### 🔎 Search Terms

unintentinal, comparison, 2367, overlap

### 🕗 Version & Regression Information

- typescript: `v7.0.2`
- node: `v24.14.1`
- pnpm: `v12.3.4`

### ⏯ Playground Link

_No response_

### 💻 Code

```ts
let n: "a" | "b" = "a";

const updateN = () => {
n = "b";
};

// This comparison appears to be unintentional because the types '"a"' and '"b"' have no overlap. [2367]
if (n === "b") {}

updateN();

// This comparison appears to be unintentional because the types '"a"' and '"b"' have no overlap. [2367]
if (n === "b") {}

n = "b";

// No error
if (n === "b") {}
```

### 🙁 Actual behavior

If a variable of type `"a" | "b"` is changed in a function with closure, the LSP fails to catch the change, and assumes that it was never changed.

### 🙂 Expected behavior

No error warning, since code works as expected

### Additional information about the issue

_No response_

TypeScript v7.0.2 で issue の closure の例を再現し、diagnostic 2367 を出力する type-checker の経路を調査します。updateN をまたいで control-flow narrowing がどのように処理されるかを追跡し、両方の比較を対象とする回帰テストを追加します。closure 呼び出し後の比較で誤検知の警告が発生せず、同時に例が引き続き正しくチェックされれば完了です。

索引モデルが issue の本文から書いたものです。