Type-narrowing based on instance type

Bug Report

I would like to do a form of type narrowing based on the instance type. Minimal example in the script below.

mypy tells me that my script is not a valid pattern though. Is this true, or is it a bug?

To Reproduce

from typing import overload, Protocol, Self

class HasOverride(Protocol):
    override: bool

class A():
       
    @overload
    def fake_method(self: HasOverride) -> "A":
        ...
    
    @overload
    def fake_method(self) -> Self:
        ...
        
    def fake_method(self) -> Self | "A":
        if hasattr(self, 'override'):
            return A()
        return self
    
class B(A):  # fake_method should return B
    pass

class C(A):  # fake_method should return A
    override = True

Expected Behavior

mypy 1.16.0 raises the following error:

error: Overloaded function implementation cannot satisfy signature 1 due to inconsistencies in how they use type variables [misc]

pyright 1.1.403 does not raise an error.

It seems reasonable to me to allow this pattern, which is why I am opening this as a bug report.

If this is in fact desired behaviour, I would be very grateful for an explanation and, if possible, a suggested alternative pattern (I'm a bit desperate!).

Actual Behavior

Your Environment

• Mypy version used: 1.16.0 (but have also repeated on 1.17.1)
• Mypy command-line flags: just mypy (from a clean environment I pip installed mypy and then ran `mypy on the script above)
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.11.13

Start with the minimal Python script in the report and run it with mypy 1.16.0 or 1.17.1 using the default command, then compare the result with pyright 1.1.403. Trace the overload implementation consistency check and determine whether the reported pattern should be accepted; done means a resolved behavior with coverage for this example.