notmuch-emacs inline image display broken in emacs-29

[Alex Murray <alex.murray@canonical.com>]

Hi folks,

I have noticed that inline image display doesn't work anymore in
emacs-29 / git master and have tracked it down to a change to the way
mm-inline-image inserts an image into the buffer.

In
https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=d2186160a9e978960c0f96bc3b4fc65b5affc170
mm-inline-image was changed to use insert-image instead of
put-image. This inserts the image into the buffer using a single space
as the string contents with a display property set as the image contents
so that the single space is not shown itself but instead the image is
shown in its place.

I had thought the culprit then was the use of
notmuch-wash-elide-blank-lines within the default value of
notmuch-show-insert-text/plain-hook - assuming that since the line
containing the image is now just a single space, it then gets deleted
from the buffer and the image is never shown. However, even after
setting notmuch-show-insert-text/plain-hook to nil, images are still not
shown inline by notmuch.

However, if I locally redefine mm-inline-image to use say a period "."
as the string argument to insert-image then the image appears as
expected.

Any thoughts on what may be happening here and how best to resolve this?

Thanks,
Alex