Problem inferring type variables with a default in `Protocol`

[cmp0xff]

Describe the bug

pyright does not infer the type variable with a default properly when it comes to a Protocol.

Code or Screenshots

ttest.py:

from typing import Any, Generic, Protocol
from typing_extensions import Self, reveal_type, TypeVar

T_co = TypeVar("T_co", covariant=True)
S1 = TypeVar("S1", default=Any)


class SupportRou(Protocol[T_co]):
    def __rou__(self) -> T_co: ...


def rou(obj: SupportRou[T_co]) -> T_co:
    return obj.__rou__()


class Series(Generic[S1]):
    def __rou__(self) -> Self:
        return self


reveal_type(rou(Series()))  # pyright gives Series[Unknown], mypy gives Series[Any]

reveal_type(rou(Series[int]()))  # pyright and mypy both give Series[int]

VS Code extension or command-line

poetry run pyright ttest.py

I have pyright 1.1.407, python 3.10.11 or 3.14.2