Descriptions are not being passed to documentation page for types

Many of the items documented at https://shiny.posit.co/py/api/MiscTypes.html have descriptions in the source code, but these descriptions do not appear in the function reference, even though other elements of the documentation do.

For example, the source code for types.ImgData includes

class ImgData(TypedDict):
    """
    Return type for :func:`~shiny.render.image`.

    See Also
    --------
    ~shiny.render.image

    Example
    -------
    See :func:`~shiny.render.image`.
    """

    src: str
    """The ``src`` attribute of the ``<img>`` tag."""
    width: NotRequired[str | float]
    """The ``width`` attribute of the ``<img>`` tag."""
    height: NotRequired[str | float]
    """The ``height`` attribute of the ``<img>`` tag."""
    alt: NotRequired[str]
    """The ``alt`` attribute of the ``<img>`` tag."""
    style: NotRequired[str]
    """The ``style`` attribute of the ``<img>`` tag."""
    coordmap: NotRequired[Any]
    """TODO """

but the description in the first line does not appear in the rendered documentation:

Start with shiny/types.py and compare the ImgData source docstrings with the rendered MiscTypes.html entry for shiny.types.ImgData. Trace the documentation build path that produces this page and run it locally; done means the type and field descriptions shown in the source appear in the generated function reference.