silent crash with generic bound to itself

```py
from typing import TypeVar

Int = TypeVar("Int", bound=Int)

def f(i: Int): ...
```

Reproduce the issue with the provided Python snippet and determine how basedmypy handles a TypeVar whose bound refers to itself. Trace the checker behavior from that input and identify the expected non-silent outcome. Done means the snippet is handled without a silent crash and the behavior is covered by a regression test.

Written by the indexing model from the issue text.