Fetches immediately on connect and is the only timing that emits a <link rel="preload" as="fetch"> hint, which the runtime reuses so there is one server render.

Waits for requestIdleCallback before fetching. No preload hint.

Fetches when the media query matches. On any normal window this matches at once.

The greeting below is a deferred server island. During its render on the endpoint it reads your pg_name cookie (defaulting to voyager) — cookies flow because the fetch is same-origin. Set a name and reload: the island re-renders with it. No component JS ships for the greeting.

This hole does not fetch until it scrolls into view. The server does no work for content nobody reached. Scroll down past the spacer to trigger it.