`!= (None, None)` Narrowing only in else branch

Bug Report

!= (None, None) correctly narrows the else branch to tuple[None, None] but, doesn't narrow the union in the if branch.

To Reproduce

a: tuple[int, str] | tuple[None, None]

if a != (None, None):
    reveal_type(a)  #  Revealed type is "tuple[int, str] | tuple[None, None]"
else:
    reveal_type(a)  #  Revealed type is "tuple[None, None]"

Expected Behavior

The if branch should narrow to tuple[int, str]

Actual Behavior

The if branch is tuple[int, str] | tuple[None, None]

Your Environment

• Mypy version used: 2.1
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used:

Start by reproducing the issue's tuple-union example and inspect mypy's type-narrowing handling for inequality comparisons. Add or update a regression test for a != (None, None); done means the if branch reveals tuple[int, str] while the else branch remains tuple[None, None].