In-buffer completion of EBDB mail addresses with corfu

[Arash Esbati <arash@gnu.org>]

Hi all,

almost a year ago, I asked here about using corfu for in-buffer
completion of mail addresses in BBDB database.  I got that working
somehow, bug now I switched to EBDB (soley because it has a manual ;-)
and now I have the same problem: Does anybody has a working solution how
to get in-buffer completion working in Message mode?  In a *unsent mail*
buffer, I want:

  To: <Point-here-hit-TAB offers mail addresses with corfu>

It seems EBDB works in general; if I go to the "To: " header and do

  M-x edbd-complete-mail RET

I get a *Completions* buffer where I can choose from.

After this question[1], there was also a bug report #59314[2] that EUDC
has some issues with header completion, but it seems there was no real
solution?

This is with EBDB v0.8.18 installed from ELPA and Emacs 30 from master
(98748aa6e6) and zero customization for EBDB.  The value of
`completion-at-point-functions' is:

  completion-at-point-functions is a variable defined in ‘minibuffer.el’.

  Its value is (message-completion-function t)
  Local in buffer *unsent mail*; global value is 
  (tags-completion-at-point-function cape-file)

TIA.  Best, Arash

Footnotes:
[1]  Message-ID: <87r0y42vnh.fsf@a16n.net>

[2]  https://debbugs.gnu.org/cgi/bugreport.cgi?bug=59314