Keys and values could be narrower for closed TypedDicts

I was very excited to try out mypy 2.2 with the initial support for the TypedDict closed keyword.
But in our code base, where we often iterate over TypedDicts, it did not help much because the keys and values are still inferred as str and object, respectively.

from typing_extensions import TypedDict, reveal_type


class Closed(TypedDict, closed=True, total=False):
    a: int
    b: str

c = Closed(a=1, b='a')
reveal_type(c.items())

for key, val in c.items():
    c[key]

$ mypy --pretty test.py
test.py:9: note: Revealed type is "_collections_abc.dict_items[str, object]"
test.py:12: error: TypedDict key must be a string literal; expected one of ("a", "b")  [literal-required]
        c[key]
          ^~~
Found 1 error in 1 file (checked 1 source file)

ty narrows both keys and values here

$ ty check test.py
ty check test.py 
info[revealed-type]: Revealed type
 --> test.py:9:13
  |
9 | reveal_type(c.items())
  |             ^^^^^^^^^^ `dict_items[Literal["a", "b"], int | str]`
  |

Found 1 diagnostic

Start by reproducing the issue's test.py example with mypy --pretty, focusing on TypedDict.items() and the subsequent c[key] access. Trace the TypedDict type-checking path responsible for these inferred types; done means closed TypedDict iteration reveals a literal union of keys and corresponding value types, and indexing with the iterated key is accepted.