Narrowing dict to TypedDict

I want to narrow an unambiguously defined dict[...] type in a superclass to a specific TypedDict in an inheriting class but I cannot figure out a way to specify a dict-based supertype that the TypedDict can get assigned to. I'm using pylance (standard).

The following works fine:

from typing import TypedDict

Base_t = TypedDict('Base_t', {})

class Base[T: Base_t]:
    def get(self) -> T:
        ...

class Implementation_t(TypedDict):
    one: str
    two: int

class Implementation[U: Implementation_t](Base[U]):
    def get(self) -> U:
        ...

However, if I want to specify Base_t more narrowly (i.e. specify the types of the map), along the idea of:

type Base_t = dict[str, str|int]

the type checker fails assigning Implementation_t to Base_t. I need a way to define a supertype to the TypedDict Implementation_t that specifies key & value types but not any specific fields.

N.B.: Naturally, Implementation_t's key and value types are subsets of Base_t's, respectively.

Is there a nice way to connotate this?