bug#81645: 32.0.50; Annotations break *Completions* navigation in vertical format

> Cc: Eli Zaretskii <[email protected]>, Sean Whitton <[email protected]>
> From: Stephen Berman <[email protected]>
> Date: Mon, 17 Aug 2026 16:06:06 +0200
> 
> 0. emacs -Q
> 1. (setopt completions-format 'vertical)
> 2. Sanity check: Typing `M-x auto- TAB' pops up the *Completions* buffer
>    and you can navigate up and down through each column by typing
>    `M-<DOWN>' and `M-<UP>' with wrapping from the last to the first
>    candidate and vice versa.
> 3. Now type `M-x abbrev- TAB', then repeatedly type `M-<DOWN>': after
>    the last candidate point wraps to the second instead of the first
>    candidate.
> 4. Now type `M-x dabbrev- TAB'.  Now typing `M-<DOWN>' once moves to
>    last candidate, but repeating `M-<DOWN>' does not move point (in
>    particular, no wrapping).  Now typing `M-<UP>' moves point back to
>    the first candidate, but typing `M-<UP>' again move point not to the
>    beginning of the last candidate but to the middle of the annotation
>    "(M-/)" affixed to the candidate.
> 
> The problems in 3 and 4 are due to the annotations in the *Completions*
> buffer.  The attached patch fixes these problems, so that navigation in
> 3 and 4 work as in 2 according to my testing.  I think this patch should
> be applied to the release branch because the type of navigation in
> vertical format illustrated by 2 was introduced in Emacs 31 by commit
> 77ca60b48d01, which, however, failed to take annotations into account.

I think this is fine to install on the emacs-31 release branch,
because the code it changes is specific to the 'vertical'
completions-format, which is new in Emacs 31.

Sean?