is possible to tell mypy that this function guaranty this other condition?

I have some classes that more or less can be reduced to this example

from typing import Protocol, Callable, Any, runtime_checkable

@runtime_checkable
class Loader(Protocol):
    def load(self,*a,**k) -> Any:...

class Foo:
    def __init__(self, path:str, loader:Loader|None) -> None:
        self.path = path
        self.loader = loader 
    
    @property    
    def loader(self) -> Loader | None:
        return self._loader
    @loader.setter
    def loader(self, value:Loader|None) -> None:
        if value and not isinstance(value,Loader):
            raise ValueError
        self._loader = value

class Baz(Foo):
    
    def prepare(self) -> Callable[...,Any] | None:
        if not hasattr(self.loader,"load"):
            return None
        ...#prepare
        return lambda x:x #for example purposes
    
    def do_stuff(self) -> Any:
        if (pre:=self.prepare()):
            a = pre()
            #assert self.loader is not None
            return self.loader.load(a)
        ...#do stuff without the loader

when tested with mypy give me

test9.py:33: error: Item "None" of "Optional[Loader]" has no attribute "load"
Found 1 error in 1 file (checked 1 source file)   

is there a way to tell mypy that if the prepare method return something also means that self.loader is non-None?

(other than uncommenting that assert or type ignore or something else that result in some useless runtime piece of code that does nothing such as cast)