school_compare/nextjs-app/components/Illustration.tsx

/**
 * The landing hero artwork.
 *
 * This is the supplied illustration, not a drawing of one — see
 * assets/hero-source.png and scripts/build-hero-images.js, which produces
 * everything under public/brand/hero-*. Regenerate rather than hand-editing.
 *
 * Server-safe by construction: no 'use client', no hooks, no handlers, so it
 * renders in the RSC pass and never reaches the client bundle.
 *
 * TWO CROPS, ONE <picture>
 * ------------------------
 * The slot is two different shapes. On desktop the artwork sits behind the
 * whole panel at roughly 2.1:1 → 2.7:1, with the headline over the empty cream
 * area the illustration reserves on its left. Below the one-column breakpoint
 * it becomes a band between 2.6:1 and 4.9:1, under the search rather than
 * behind it.
 *
 * A single file under `object-fit: cover` centre-crops, and at the band's
 * extreme that slices a strip through the middle of the scene and loses the
 * schoolhouse — exactly how the previous SVG hero failed on phones. So the
 * <source media> switches crop, not just resolution: `band` is pre-cropped
 * around the school and is already near 2.6:1, so the narrow band barely
 * crops it further.
 *
 * `object-position` is set in CSS per breakpoint and is load-bearing — see
 * .heroArt in HomeView.module.css.
 *
 * The artwork is decorative: the proposition beside it carries the meaning, so
 * alt is empty and it is hidden from assistive tech rather than described.
 */

/*
 * The panel is not the viewport. `.main` is capped at 1400px with 1.5rem of
 * padding (1rem under 768px), so the artwork's box is that minus the padding —
 * describing it as 100vw over-requests by ~48px worth of candidate at every
 * width, which on a slow connection is a larger file than needed for the LCP
 * element.
 */
const SIZES = '(min-width: 1400px) 1352px, (min-width: 769px) calc(100vw - 3rem), calc(100vw - 2rem)';

/** Intrinsic size of the wide crop — the aspect hint that prevents reflow. */
const WIDE_W = 1672;
const WIDE_H = 941;

export function HeroIllustration() {
  return (
    <picture>
      {/* Band crop first: <source> is first-match-wins, so the narrow-viewport
          rules have to precede the unconstrained desktop ones. */}
      <source
        media="(max-width: 860px)"
        type="image/avif"
        srcSet="/brand/hero-band-500.avif 500w, /brand/hero-band-700.avif 700w, /brand/hero-band-972.avif 972w"
        sizes={SIZES}
      />
      <source
        media="(max-width: 860px)"
        type="image/webp"
        srcSet="/brand/hero-band-500.webp 500w, /brand/hero-band-700.webp 700w, /brand/hero-band-972.webp 972w"
        sizes={SIZES}
      />
      {/*
        The band's JPEG, and the reason it exists.

        <img src> cannot vary by viewport, so it is always the wide crop. A
        browser that takes neither AVIF nor WebP would therefore fall through
        to the desktop frame on a phone and lose the schoolhouse — the exact
        failure this whole component is arranged to prevent, surviving in the
        one path nobody looks at. No `type` here, so it matches anywhere the
        media query does, and it sits after the modern formats so they still
        win where supported.
      */}
      <source media="(max-width: 860px)" srcSet="/brand/hero-band-700.jpg" />
      <source
        type="image/avif"
        srcSet="/brand/hero-wide-900.avif 900w, /brand/hero-wide-1200.avif 1200w, /brand/hero-wide-1672.avif 1672w"
        sizes={SIZES}
      />
      <source
        type="image/webp"
        srcSet="/brand/hero-wide-900.webp 900w, /brand/hero-wide-1200.webp 1200w, /brand/hero-wide-1672.webp 1672w"
        sizes={SIZES}
      />
      {/*
        The hero is the largest thing above the fold, so it is almost certainly
        the LCP element: fetchPriority high, and never lazy. eslint's
        no-img-element wants next/image, which cannot art-direct between two
        different crops — that is the whole point of the <picture> above.
      */}
      {/* eslint-disable-next-line @next/next/no-img-element */}
      <img
        src="/brand/hero-wide-1200.jpg"
        alt=""
        aria-hidden="true"
        width={WIDE_W}
        height={WIDE_H}
        decoding="async"
        fetchPriority="high"
      />
    </picture>
  );
}