from contextlib import contextmanager
from typing import Iterator


@contextmanager
def add_source_channel[T](source: list[T]) -> Iterator[list[T]]: ...

t: list[int] = [1]
m = add_source_channel(t) # not working  ->  _GeneratorContextManager[list[Unknown], None, None] 
# should be _GeneratorContextManager[list[int], None, None] 


def add_source_channel2[T](source: list[T]) -> Iterator[list[T]]: ...

m = add_source_channel2(t) # working just fine