[YeungKC]

Summary

After #2070, Latin text and shared punctuation (—, “ ”) on Linux use the Noto Sans CJK glyphs, so the dashes and quotes in Chinese text are full width.

Before #2070, the theme kept the Material fallbacks for Linux ('Ubuntu', 'Adwaita Sans', 'Cantarell', 'DejaVu Sans', …), and Latin text used the first installed one. #2070 replaced these fallbacks with the CJK and emoji families. 77b8484 restored 'Roboto' as the main family, but 'Roboto' is not installed, so the CJK family still draws Latin text.

 withFallbackFonts() on Linux
-  fontFamily: loadedFallbackFonts            // null → 'Roboto', not installed
+  fontFamily: loadedFallbackFonts ?? fc-match('Ubuntu,Adwaita Sans,Cantarell,…')
-  fontFamilyFallback: [CJK family, emoji family]
+  fontFamilyFallback: [emoji family, CJK family]

• The list comes from Typography.material2021(platform: TargetPlatform.linux), so it is not copied into the app.
• The main family is installed, so the first layout does not search for the missing 'Roboto'.
• _warmLinuxFonts warms the same main family.
• The emoji family is now before the CJK family. The CJK fonts have black and white glyphs for some emoji (for example 🅿 U+1F17F). With the CJK family first, these emoji lost their color after Keep desktop frames within the 120 Hz budget #2070. With this order, the emoji rows match the version before Keep desktop frames within the 120 Hz budget #2070. Only a few CJK symbols that also have an emoji glyph (㊗ ㊙ 〰 〽) change: before Keep desktop frames within the 120 Hz budget #2070 they were black and white, now they are in color. The theme still does not follow U+FE0F (VS16), so ❤️ stays black and white, as before Keep desktop frames within the 120 Hz budget #2070.

Evidence

Arch Linux, system language en_US. A small entry point renders fixed sample text (English, Chinese, mixed, emoji with and without U+FE0F, CJK symbols; weights 400, 500, 700; app locale zh_CN and en_US) with the app's loadFallbackFonts() and withFallbackFonts() from each version:

• Before: 594e4dd (Keep desktop frames within the 120 Hz budget #2070) and 77b8484: Latin text in Noto Sans CJK, full-width — and “ ”. The two are pixel-identical.
  After: text and punctuation are the same as the version before Keep desktop frames within the 120 Hz budget #2070 (594e4dd^). The emoji rows are also the same. Only ㊗ ㊙ 〰 〽 differ, as described above.
  Each image: app locale zh_CN (top) and en_US (bottom); bodyMedium 400, bodyMedium 500 and titleMedium 700.

Before #2070 (594e4dd^)	After #2070 (594e4dd)
main (77b8484)	This PR

• flutter analyze: no issues. flutter test: 327 passed.

Not tested on Ubuntu.

Merge Danger

Door: two-way

Blast Radius: Linux text

Only Linux changes. With a non-English system language, the theme still uses the font family that the app loads from fc-match.

[Copilot]

🟢 Approval recommended

The focused change preserves existing font precedence and platform behavior, with no blocking issues identified.

No open issues 🎉

What changed in this PR

Restores Linux’s Material fallback font as the theme’s main font, correcting Latin text and punctuation rendering while retaining CJK and emoji fallbacks.

Changes:

• Resolves an installed font from Material’s Linux fallback list.
• Uses the same main font for theme text and font warmup, preserving loaded-font precedence.

File	Description
lib/​utils/​system/​system_fonts.dart	Resolves and applies the Linux main font consistently.

_{Review effort: Balanced}