With a new syntax generic function, `T` cannot be used to set a default value to a parameter with `cast()` while `T` can be used for a parameter and return type

*Memo:
mypy --strict test.py
mypy 1.19.0
Python 3.14.0
Windows 11

With a new syntax generic function, T cannot be used to set a default value to a parameter with cast() while T can be used for a parameter and return type as shown below:

from typing import cast

                      # ↓ Error
def func[T](x: T = cast(T, 100)) -> T:
    return x # ↑ No error         # ↑ No error

error: Name "T" is not defined

If I don't use T with cast(), other error occurs as shown below:

                 # ↓↓↓ Error
def func[T](x: T = 100) -> T:
    return x

error: Incompatible default for argument "x" (default has type "int", argument has type "T")

Start with the test.py reproducer and run it with mypy --strict using the reported mypy 1.19.0 and Python 3.14.0 versions. Trace how the new generic-function syntax handles T in the default expression passed to cast(). Done means the example accepts the cast-based default while preserving the existing parameter and return type behavior.