perf(web): fix Lighthouse Speed Index — replace spinner with SVG PE-grid skeleton#15
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The landing page skeleton was an empty spinner, causing Lighthouse Speed Index to score 0 (7.8 s) while WASM downloaded. Replaced it with a static SVG that mirrors the exact PEGrid layout (4×4 cells at the same CELL/GAP/offsets and CSS color vars) so the page is visually complete at FCP (~0.8 s). Also added opt-in preloadWasm prop to Layout.astro to emit <link rel="preload" as="fetch"> for tiny_tpu.wasm on WASM-using pages, starting the binary download earlier during HTML parse. Affected: LandingEmbed.tsx, Layout.astro, index.astro, app.astro
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Summary
LandingEmbedwith a static SVG that mirrors the exactPEGridlayout (4×4 cells, sameCELL/GAP/offset constants, same CSS color vars) — page is visually complete at FCP (~0.8 s) instead of after WASM loads (~7–8 s)preloadWasmprop toLayout.astrothat emits<link rel="preload" as="fetch" href="/tiny_tpu.wasm">to start the binary download during HTML parse rather than after React hydrationweb/.gitignoreto exclude the.vercellocal-link directoryWhy
Lighthouse Speed Index scored 0 (7.8 s) on the first deploy because the skeleton left the hero section visually empty while WASM downloaded. All other metrics (FCP, LCP, TBT, CLS, TTI) were already excellent. This change makes the page appear complete immediately at FCP, targeting Speed Index ≤ 1.5 s and overall Performance ≥ 90.
Test plan
/— Performance ≥ 90, Speed Index ≤ 2 spnpm lint && pnpm typecheck && pnpm build— all clean