Fonts missing from Chromium MHTML saves (known Chromium bug)

Problem

When saving pages as MHTML using Chromium (including via Playwright or CDP's Page.captureSnapshot), web fonts are frequently missing from the archive. The @font-face declarations in CSS reference font files by URL path, but the actual font binaries are not included as MIME parts.

Root cause

This is a known, long-standing Chromium bug: chromium issue 40219015

Chromium's FrameSerializer has code to embed fonts (AddFontToResources()), but it checks font.IsLoaded() and font.ResourceBuffer() at save time. If a font was lazily loaded or has been evicted from the resource cache, it is silently skipped. There is no Chrome flag or setting to control this behavior.

Workarounds

• Ensuring all fonts are fully loaded before saving (e.g., using document.fonts.ready in Playwright) may improve results, but is not guaranteed.
• SingleFile (browser extension) actively fetches and embeds all resources including fonts, but is not usable in headless/Playwright workflows.

References

• Chromium Issue 40219015: MHTML serialized page misses non-data: @font-face resources
• MHTML in Chromium — textslashplain.com

The issue names no repository file, test, or entry point. Start by reviewing Chromium issue 40219015 and reproducing an MHTML save with a web font; done would require a confirmed project-level workaround or an upstream Chromium fix.