A theme's <a:fontScheme> carries latin, ea (East Asian) and cs (complex
script) typefaces for each of the major and minor fonts. The model held
only the latin ones and the writer emitted <a:ea typeface=""/> and
<a:cs typeface=""/> unconditionally, so a Japanese workbook's theme fonts
(e.g. 游ゴシック, ＭＳ Ｐゴシック) were silently deleted on open + save.
Theme gains major_font_ea, minor_font_ea, major_font_cs and
minor_font_cs (#[serde(default)], so older GridCraft JSON still loads;
empty means the file did not set one). The XLSX reader and writer
round-trip them escaped, and a theme without them writes exactly the
empty attributes it wrote before.
Rendering and font resolution are unchanged: the UI does not consume ea
yet, and wiring it in is a follow-up.
Mouhand-Kaddo