The viewer inherits `src: url('/fonts/Inter.woff2')` from the shared theme CSS. That is
correct for the app, which serves `static/fonts/` from the site root — but the keepsake is
opened from file:// off a USB stick or a Downloads folder, where `/fonts/...` resolves to
the root of the guest's DISK. Both requests 404, and `font-display: swap` makes it silent:
the viewer renders in a fallback system font with nothing server-side able to report it.
Found by opening a real released keepsake in a browser and watching `requestfailed` — no
other signal exists, which is the recurring lesson about this artifact.
Fixing it in the shared CSS would inline ~154 KB into every app page load for nothing, and
shipping a `fonts/` folder beside index.html gives the guest a directory they can break by
moving one file. So the substitution belongs in the build that knows its output has no
origin. The plugin errors the build if the theme ever stops referencing those URLs, rather
than silently shipping another keepsake in Times New Roman.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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