Opaque type for io.TextIOWrapper seek and tell?

The following prints 18446744073709551620 (as I discovered in https://github.com/python/cpython/issues/93077):

import io
stream = io.TextIOWrapper(io.BytesIO(b'"")\r\nx\r\n'))
stream.read(1)
stream.read(1)
stream.read(1)
print('-----> tell:', stream.tell())

This is not a bug. The documentation says that .tell() returns "an opaque number" that "does not usually represent a number of bytes in the underlying binary storage".

In fact, calling .seek() with anything else than 0 or a return value of .tell() "produces undefined behaviour". I just relied on that today, without knowing it. I wrote this code:

def _upgrade_high_scores_file(file: IO[str], old_version: int) -> None:
    ...
    file.seek(len(b"catris high scores file v"))
    ...

This shouldn't pass the type check IMO.

Start by reviewing the io.TextIOWrapper seek() and tell() annotations in typeshed alongside the Python documentation quoted in the issue. A complete change would represent tell() results as opaque values and prevent seek() from accepting arbitrary offsets while still allowing 0 and a value returned by tell().