Bug Report

Using isinstance(<Sequence[X]>, tuple) narrows the type of <Sequence[X]> to Tuple[Any, ...], not Tuple[X, ...] as one would expect.

To Reproduce

[mypy-play.net]
[pyright-play.net¹] (pyright handles this as expected)

from __future__ import annotations
from typing_extensions import (
        assert_type,
        Sequence,
        Tuple,
        )

value: Sequence[str]

if isinstance(value, tuple):
    assert_type(value, Tuple[str, ...])
            # expected: (this works)
            # actual: "Expression is of type 'tuple[Any, ...]',
            #          not 'tuple[str, ....]'"

Expected Behavior

if instance(value, ...) should only ever narrow the type of value

Actual Behavior

Mypy narrows the container type, but forgets the element type

Your Environment

• Mypy version used: 1.8.0; bug exists back to at least 1.0
• Mypy command-line flags: (none)
• Mypy configuration options from mypy.ini (and other config files): (none)
• Python version used: 3.8, 3.12

Existing issues

While it seems extremely unlikely that this issue hasn't been reported, I haven't been able to locate anything obviously related among the ~217 issues that mention both isinstance and tuple. Issue #2456 may be vaguely related.