`fetchFeed` cannot start until main.js has downloaded, parsed and mounted React,
so the one request this page exists to make was the last one to leave. Nothing
about the URL depends on the bundle, so the preload scanner can have it in flight
in the first few milliseconds instead.
Measured on a 4G/4x-CPU profile with a cold cache and gzip on: the events reach
the screen at ~470ms instead of ~570ms, and the loading state stops being
something a reader can see rather than merely being brief. First contentful paint
is unchanged within noise — the win is that the feed is off the critical path
entirely, arriving at 216ms while the bundle is still downloading.
`crossorigin` on that link is not decoration. `as="fetch"` has to match the
credentials mode of the `fetch()` that follows, and a mismatch is not a no-op:
the browser throws the preload away and downloads the feed twice, which is worse
than not preloading at all. Verified by counting requests in a real browser,
because no test here can see it.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
