Astro doesn't emit <link rel="modulepreload"> tags, so browsers
discover JS dependencies one hop at a time. A Vite plugin now walks
the client chunk graph at build time and injects a dependency manifest;
an Astro middleware reads it and injects modulepreload hints into
every HTML response, letting the browser fetch all modules in parallel
from the first HTML parse.
For context, see withastro/roadmap#561