Error with TypeVar with constraints on field initialization

The following example fails to type-check with mypy and pyright, but succeeds with ty:

from dataclasses import dataclass
from typing import TypeVar, Generic

class X:
    pass

class Y(X):
    pass

T = TypeVar("T", X, Y)

@dataclass
class C(Generic[T]):
    v: T

def f(c: C[T]):
    # no error with mypy and ty
    # pyright reports an error on the argument
    c.v = Y()

    # no error with mypy and ty
    # pyright reports an error on the assignment
    d: C[T] = C(Y())

class M(Generic[T]):
    # no error with ty
    # mypy and pyright report an error on the assignment
    c: C[T] = C(Y())

The constraints on T effectively make Y a lower bound for T, meaning that C(Y()) should be considered a valid C[T] for any allowed T. This seems to be correctly understood by mypy for field assignment and constructor assignment within a function, but not for field initialization at the class level.

Start with the minimal Python example in the issue and compare mypy's handling of constrained TypeVar assignments during function bodies with class-level field initialization. Reproduce the differing results from mypy, pyright, and ty, then determine whether class-level initialization should accept C(Y()) for every allowed T and add coverage for the reported cases.