Rebuild the guest "keepsake" (offline HTML gallery) so it renders when the
extracted index.html is opened over file://. Browsers block external ES-module
scripts and fetch() at origin null, so a normal multi-file SvelteKit build shows
a blank window. Build the viewer as one self-contained index.html (inlined
JS/CSS via vite-plugin-singlefile, standalone non-SvelteKit entry) and inject
the data as window.__EXPORT_DATA__; the backend embeds the built viewer via
include_dir! and writes the data global into index.html when zipping.
Also surface the guest-facing download: a feed banner and the BottomNav Export
tab, both shown once the host releases the export.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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