How to print a classical trill combining acciaccatura, TrillSpan and afterGrace

Here is an excerpt of Mozart's KV545 piano Sonata (as brought to Mutopia by A. Sierra), in which you can see the typical classical trill, i.e. beginning with an acciaccatura, then trilling the whole bar, and ending with two afterGrace notes. This combination, which is rather frequent (if not systematic) in classical piano music, requires a rather precise typesetting: first the \acciaccatura, then the \afterGrace (which you have to define using Scheme-like syntax), then the main note, the TrillSpan and the two final notes (don't forget the curly braces here). You can also notice here the \slurDown, which avoids slurs collision.

\version "2.24.0"

%% http://lsr.di.unimi.it/LSR/Item?id=290

rh = \relative c' {
  b''8-3(\f g-1) d'2-5(\sf c16 b a g)
#(define afterGraceFraction (cons 31 32))
 \acciaccatura b8-3 \slurDown \afterGrace a1  \startTrillSpan \( ( {g16[ a ] )
\stopTrillSpan}
  g4 \) r2.
}

lh = \relative c' {
  \clef treble 
  d16_5 b'_1 g_2 b \repeat unfold 3 { d, b' g b } 
  \repeat unfold 4 { d, c' fis, c' }
  <g-2 b-1>4 r2. 
}

\score {
  \new PianoStaff <<
    \new Staff \rh
    \new Staff \lh
  >>
}