Trimbox and crop marks on cover page

I want to generate a press-ready PDF book with cover with the following but
I dont seem to get the cover correct.

- Trim size 320 × 240 mm
- MediaBox enlarged using \setuppapersize[cover][oversized]
- Crop marks (marking=color)
- Artwork extending into the bleed outside the TrimBox
- I am using LMTX v. 2026.04.27 on windows 11 Pro, 25H2

1. With the minimal example below, \startMPpage is clipped to Page so the
bleed area in the enlarged MediaBox remains white
2. Is this the intended behaviour of \startMPpage? If so, what is
recommended to create artwork that extends into the bleed while keeping the
TrimBox and crop marks?

\definepapersize[cover][width=320mm,height=240mm]
\definepapersize[book][width=160mm,height=240mm]
\setuppapersize[distance=38mm]
\setuplayout[backspace=18mm, width=129mm, height=223mm, marking=color]
\setuplayout[location=middle]

\starttext
\pagebreak
\setuppapersize[cover][oversized]
%\startoverlay{
\startMPpage
StartPage;
numeric w, h, m;
w := bbwidth(Page);
h := bbheight(Page);
m := 19mm;
path p;
p := unitsquare xyscaled (w-2m,h-2m) shifted (m,m);
fill p withcolor \MPcolor{yellow};
\stopMPpage
%}\stopoverlay
\pagebreak
\setuppapersize[book][oversized]
\dorecurse{5}{\input{tufte}}
\stoptext

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