How to catch post-events inside chords in an event listener?

[Lukas-Fabian Moser]

Folks,

probably I'm being stupid:

\version "2.22"

#(define (test_engraver ctx)
   (make-engraver
    (listeners
     ((tie-event engraver event)
      (format #t "Tie encountered at ~a.\n" (ly:context-current-moment 
ctx))))))

\layout {
  \context {
    \Voice
    \consists #test_engraver
  }
}

{
  a4~
  <a~ g'> % this one is not seen by the engraver
  a~
  a
}

What do I have to do to make my custom engraver also see post-events 
(here, a tie, but in my context it's a custom event type) used inside 
chords?

Lukas