Title: Type variable reported unbound when only a ParamSpec alias's return type uses it and its ParamSpec slot is not a ParamSpec

Bug Report

A function whose return type is a generic alias over a ParamSpec, with a parameter list ([int]) or ... in the
ParamSpec slot, gets Type variable "T" is unbound for a type variable that appears only in that return type. With the
type statement the same function gets Name "T" is not defined, although T is declared in its type parameter list.

The same signature is accepted when:

• the return type is written without the alias (Callable[[int], T]);
• the alias has no ParamSpec (Callable[[int], T] aliased);
• the ParamSpec slot holds a ParamSpec;
• T also appears in a parameter.

pyright, pyrefly and ty accept all of them.

To Reproduce

from collections.abc import Callable
from typing import ParamSpec, TypeAlias, TypeVar

P = ParamSpec("P")
T = TypeVar("T")

Alias: TypeAlias = Callable[P, T]
NoParamSpec: TypeAlias = Callable[[int], T]


def plain() -> Callable[[int], T]:  # accepted
    raise NotImplementedError


def no_paramspec_alias() -> NoParamSpec[T]:  # accepted
    raise NotImplementedError


def paramspec_alias() -> Alias[[int], T]:  # error: Type variable "T" is unbound
    raise NotImplementedError

With PEP 695 syntax:

from collections.abc import Callable

type Alias[**P, T] = Callable[P, T]


def paramspec_alias[T]() -> Alias[[int], T]:  # error: Name "T" is not defined
    raise NotImplementedError


def with_paramspec[**Q, T]() -> Alias[Q, T]:  # accepted
    raise NotImplementedError

typing_extensions.TypeAliasType("Alias", Callable[P, T], type_params=(P, T)) behaves as the TypeAlias form, and
Alias[..., T] as Alias[[int], T].

Expected Behavior

No errors: paramspec_alias() returns a generic callable def [T] (int) -> T, as plain() does.

Actual Behavior

main.py:19: error: Type variable "main.T" is unbound  [valid-type]
main.py:19: note: (Hint: Use "Generic[T]" or "Protocol[T]" base class to bind "T" inside a class)
main.py:19: note: (Hint: Use "T" in function signature to bind "T" inside a function)

and, for the PEP 695 example:

main.py:6: error: Name "T" is not defined  [name-defined]

Where it comes from

A decorator-factory alias over a chain type, Dec = Callable[[Chain[P, T]], Chain[P, T2]]. A factory that applies to
any chain and keeps the item type, def identity() -> Dec[..., T, T], hits this; it has to be written with a
ParamSpec of its own, def identity() -> Dec[P, T, T].

Your Environment

• Mypy version used: 2.4.1 (compiled)
• Mypy command-line flags: none (--strict gives the same errors)
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.13 (--python-version 3.13)
• For comparison: basedpyright 1.40.2 (pyright 1.1.414), pyrefly 1.4.1 and ty 0.0.99 report no error on either file.
• Not checked on master.