[NTG-context] Cannot build plain format

[Henri Menke]

Dear list,

I'm trying to build the plain format but it fails with

    $ mtxrun --script plain --make
    [...]
    ! I can't find file `luatex-plain.tex'.

but mtxrun can find the file.

    $ mtxrun --find-file "luatex-plain.tex"
    /opt/context/tex/texmf-context/tex/generic/context/luatex/luatex-plain.tex

What am I doing wrong?

Also another question: Does LMTX come with a plain format?

Cheers, Henri