Type not narrowed on `isinstance(obj, Callable)` check

I received this bug report from a pyright user: https://github.com/microsoft/pyright/issues/2274. Mypy exhibits the same behavior, so I'm wondering whether it's a bug or the intended behavior.

In this code sample, mypy (and pyright) do not currently narrow the type of obj based on the isinstance(obj, Callable) conditional check.

from typing import Callable, Union

def some_func(obj: Union[Callable, int]):
    if isinstance(obj, Callable):
        reveal_type(obj) # Type of "obj" is "(*args: Unknown, **kwargs: Unknown) -> Unknown | int"
    else:
        reveal_type(obj) # Type of "obj" is "(*args: Unknown, **kwargs: Unknown) -> Unknown | int"

I'm wondering if there's a reason why mypy does not perform type narrowing in this case. Is there a type safety reason? Is callable() the preferred way to check for callables?

I've searched the issue database, and it doesn't appear to be an issue that anyone has previously reported.

まず、Python の再現コードを mypy で実行し、両方の分岐について明らかになった型を確認します。関連するテストやドキュメントも含めて、既存の isinstance と Callable の narrowing 動作を追跡します。完了条件は、この動作が意図されたものかどうかを明らかにし、バグである場合は、テスト済みの narrowing 結果を定義することです。