Bug in 3.141592653-2.6-0.999995 (TeX Live 2023) with fontspec and tabularray?

[Karl Berry]

    ra> I've redone the change, including the BIDI_MIXED

Thanks Ross. I have to admit I'm not sure where to go from here, though.
We really need Jonathan.

    m7> LuaTeX mostly treats fonts like a traditional TeX engine, 

Thanks very much for all that, Max. It is good to have some kind of
basis of understanding :).

    When using "harf" mode, the font and glyph processing is completely
    different 

.. and XeTeX always uses harfbuzz. Can someone who wants to pursue this
see if the original example reproduces with luatex in harf mode? I
foolishly did not think of this. If luatex+harf and xetex behave the
same, it seems to me there is no bug to fix ...

One other tidbit: the relevant XeTeX function seems to be
  getGlyphPositions
in XeTeXLayoutInterface.cpp. Which is converting various things to
points (not scaled points, I guess? Can't find the definition easily):

  positions[i].x = -engine->font->unitsToPoints(x + hbPositions[i].y_offset);
                   /* negative is forwards */

Hmm. --best, karl.