Generic method in generic class impacting type signature of unrelated method

Bug Report

MyPy's type resolution appears to get impacted by an unrelated generic method when evaluating a method.

To Reproduce

"""Mypy bug: method-level type parameter breaks unrelated method's self type.

mypy --strict mypy-bug-repro.py
mypy 1.19.1, Python 3.13.9
"""

from typing import Protocol, Self


class Read(Protocol):
    def read(self: Self) -> None: ...


class Write(Protocol):
    def write(self: Self) -> None: ...


class CopyFrom(Protocol):
    def copy_from(self: CopyFrom, src: CopyFrom) -> None: ...


class ReadWrite(Read, Write, Protocol):
    pass


class Store[B: Read | Write | CopyFrom]:
    def read(self: Store[Read]) -> None: ...
    def copy_from[T: CopyFrom](self: Store[T], src: Store[T]) -> None: ...


def test(store: Store[ReadWrite]) -> None:
    store.read()  # Error: Invalid self argument

Expected Behavior

Expected mypy to be happy

Actual Behavior

mypy --strict --warn-unreachable --extra-checks returns;

error: Invalid self argument "Store[ReadWrite]" to attribute function "read" with type "Callable[[Store[Read]], None]"  [misc]

Removing Store.copy_from fixes this.
Replacing test def with def test(store: Store[Read]) -> None: fixes this
Replacing Store.copy_from with the following fixes it as well;

type T = CopyFrom
class Store[B: Read | Write | CopyFrom]:
    def read(self: Store[Read]) -> None: ...
    def copy_from(self: Store[T], src: Store[T]) -> None: ...

Your Environment

• Mypy version used: mypy 1.19.1 (compiled: yes)
• Mypy command-line flags: --strict --warn-unreachable --extra-checks
• Mypy configuration options from mypy.ini (and other config files):

[tool.mypy]
plugins = ["pydantic.mypy"]
exclude = ["build-resources"]

• Python version used: Python 3.13.9

Start by running the provided Store[ReadWrite] reproduction with mypy 1.19.1 and the listed strictness flags, then trace how the generic Store.copy_from method affects the self type of Store.read. Done means the reproduction no longer reports an invalid self argument while the generic behavior remains correct, with regression coverage for this case.