`Never` inferred in complex situation with variadic callable protocol

Bug Report

Mypy is inferring a Never in a bit of a complicated setup involving TypeVarTuple, __call__ protocols and a regular TypeVar. If an annotated assignment is present it is able to check that they match. But when a bare call is done, it infers Never and always produces an error. This is a simplified version of Trio's Nursery.start() async spawn method, which I'm trying to type. (See src/trio/_core/_run.py.) I simplified it a little, removing an overload and making it synchronous.

To Reproduce

from typing import Generic, TypeVar, Protocol
from typing_extensions import TypeVarTuple, Unpack

PosArgT = TypeVarTuple("PosArgT")
StatusT = TypeVar("StatusT")
StatusT_co = TypeVar("StatusT_co", covariant=True)
StatusT_contra = TypeVar("StatusT_contra", contravariant=True)

class TaskStatus(Generic[StatusT_contra]):
    def started(self, value: StatusT_contra) -> None: ...

class NurseryStartFunc(Protocol[Unpack[PosArgT], StatusT_co]):
    def __call__(
        self,
        *args: Unpack[PosArgT],
        task_status: TaskStatus[StatusT_co],
    ) -> object: ...

def nursery_start(
    async_fn: NurseryStartFunc[Unpack[PosArgT], StatusT],
    *args: Unpack[PosArgT],
) -> StatusT:  ...

def task(a: int, b: str, *, task_status: TaskStatus[set[str]]) -> None: ...

def test() -> None:
    a_task: NurseryStartFunc[int, str, set[str]] = task  # task implements the protocol
    result: set[str] = nursery_start(task, 1, "b")  # If result is annotated this works.
    result = nursery_start(task, "a", 2)  # Detects invalid call correctly
    # Without assignment or if unnanotated, infers Never as return type?
    nursery_start(task, 1, "b")

https://mypy-play.net/?mypy=latest&python=3.11&gist=31be4208e294eb6c5cbc7390f4a836f4

Expected Behavior

Ideally Mypy would be able to propagate the typevar in TaskStatus to determine the return type, and verify that appropriate types were passed for *args.

Actual Behavior

(Last two statements)
main.py:39: error: Argument 1 to "nursery_start" has incompatible type "Callable[[int, str, NamedArg(TaskStatus[set[str]], 'task_status')], None]"; expected "NurseryStartFunc[str, int, set[str]]"  [arg-type]
main.py:41: error: Argument 1 to "nursery_start" has incompatible type "Callable[[int, str, NamedArg(TaskStatus[set[str]], 'task_status')], None]"; expected "NurseryStartFunc[int, str, Never]"  [arg-type]

The first error is correct, showing that Mypy can understand the types somewhat. But in the second case it's strangely producing Never, when it should really be effectively Any - the type is unused so it doesn't matter what it is.

Your Environment

• Mypy version used: 1.7.0, also tried master
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.8, 3.11

Ejecuta la reproducción de Python proporcionada con el ejemplo enlazado de mypy-play y compara los casos anotado y bare-call. Empieza rastreando la inferencia de tipos para TypeVarTuple, el protocolo Callable y TaskStatus en este ejemplo. La tarea estará terminada cuando la llamada bare call válida ya no informe de un Never inferido, mientras que el orden de argumentos no válido siga siendo rechazado.