In-body images size to the measure

A Markdown image asks for variants wider than it is drawn.

_markup/render-image.html:21 and _shortcodes/img.html:34 wrote the hint (min-width: 1024px) 100vw, 50vw, and both laddered from 320 to 1920 (render-image.html:19, img.html:2). The images they write sit inside the .prose block of page/content.html, capped at --prose-measure, the 65ch a page hero takes too (p2-is-hero-images-use-the-prose-measure), so the hint named a box about three times the one the browser draws and offered widths that measure can never select.

Measured before the change: 51 in-body bigImgDiv pictures, of which 7 offered a variant wider than 1280w, 5 at 1600w and 2 at 1920w. The two 1920w webp files weigh 136 KB and 97 KB, and are the widest a browser can pick for a picture 600 pixels wide.

In-body images size to the measure

• The Markdown render hook names the prose measure in its sizes hint and stops its ladder at 1280, as a hero does.
• The img shortcode sizes to the same box, and keeps the parameters it documents: holder, phn, rounds, hint, filter and simple.
• The hint and the ladder are stated once. images/boxes.html returns the boxes the theme draws an image in, prose and card, each a sizes hint and a widths ladder, and every path reads one: featured-image.html the hero’s, render-image.html and img.html the prose’s, card.html the card’s. The strings that were inline in those four callers are gone.
• image-variants.html takes a box as its caller’s contract: it asks for sizes and widths and calls errorf when one is missing, so a path that invents its own box fails the build instead of drifting. The 320-1920 fallback ladder it used to carry is deleted.

Acceptance Criteria

• No srcset in public/ offers a variant wider than 1280w: 0 of the 51 in-body pictures, whose widest entries are now 320w (2), 960w (42) and 1280w (7), and 0 of the 20 heroes.
• Every in-body picture names a box: 2 distinct sizes values across the site, the prose box and the card box, and no sizes of an image inside .prose reports a full viewport width.
• A card is unchanged: public/post/index.html keeps its grid hint and its ladder to 960.
• Hugo generates fewer variants: Processed images falls from 384 to 366.
• pnpm run test passes, html-validate included.

Notes

• The original third criterion asked after dashboard/raw/all-html-elements.html, the CSS test page. That page is not in content/, and there is no dashboard section, so the check is dropped; every image the site draws is in one of the three boxes boxes.html names, the prose, a card and a hero.
• No content calls the img shortcode, so that path is covered by the build only, not by a rendered page.
• The picture markup is still written three times, in image-variants.html, render-image.html and img.html, each with its own placeholder key: image-variants.html keys on md5 .RelPermalink and the other two on md5 .Name, which is why a card’s LQIP is missing (p2-is-card-lqip-placeholder-unused). Folding the three into one writer settles that card too; this card only stopped the widths drifting.