Llistats de codi i tecles sense blocs de codi

// ═══ Postext Cookbook · Nº 048 · Code listings and keycaps without code blocks ═══
// https://postext.dev/en/cookbook/code-listings-and-keycaps
// Code: MIT · Text: original (CC BY 4.0) · Pictures: none
// Fonts: Charis SIL, Sora, JetBrains Mono (SIL OFL 1.1) · Needs postext ≥ 1.4.1
import { buildDocument, renderPageToCanvas, clearMeasurementCache } from 'https://esm.sh/postext';

const LANG = 'es'; // @lang: the language of the sample document ('en' | 'es')
const RECIPE = 'code-listings-and-keycaps';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
const palette = { ink: '#1b1f24', muted: '#5c636b', ember: '#9a5410', // text, heads, accent
  night: '#0e1116', code: '#d3d9df', amber: '#f2b134', phosphor: '#3ddc84', // the listings
  slate: '#8a939d' }; // comments in a listing, the outline of a key (code is its face)
// Design elements read the hex, not the palette id (gotcha: palette-skips-designs).
const col = (id) => ({ hex: palette[id], model: 'hex', paletteId: id });
// The engine's defaults link to 'main-color': point it at the accent, so nothing prints blue.
const colorPalette = Object.entries({ ...palette, 'main-color': palette.ember })
  .map(([id, hex]) => ({ id, name: id, value: { hex, model: 'hex' } }));
const [TEXT, DISPLAY, MONO] = ['Charis SIL', 'Sora', 'JetBrains Mono'];
const LEAD = 14.5; // pt: the body leading, the page's baseline grid
const [NBSP, ZERO] = ['\u00a0', pt(0)];

// #region answer: a fenced block becomes a dark box with one escaped paragraph per line
// Postext sets no fenced code, so the Markdown is rewritten before the build:
// ```bash backup.sh … ``` → :::callout{type="listing" label="backup.sh"} … :::
// Characters Markdown would read as emphasis, a superscript or subscript, code or maths get
// a backslash (gotcha: dollar-math). The parser drops a backslash only before those, so any
// other backslash in the code prints as typed. ']\u2060(' keeps '[a](b)' from becoming a link.
const escape = (text) => text.replace(/[*_^~`$]/g, '\\$&').replace(/\]\(/g, ']\u2060(');
function codeLine(line, lang) {
  // A word joiner (U+2060) opens every line, so a leading '#', '-', '1.' or '>' stays text
  // (gotcha: digit-period-list). Parsing trims leading spaces, no-break ones included;
  // the word joiner in front keeps them.
  const indent = line.match(/^ */)[0].length; // indent listings with spaces, not tabs
  const body = (lang === 'console' ? session : paint)(line.slice(indent));
  const runs = body.replace(/ {2,}/g, (run) => NBSP.repeat(run.length)); // output columns
  return `\u2060${NBSP.repeat(indent)}${runs}`;
}
// The label stops at a double quote, which would close the attribute.
const listings = (markdown) => markdown.replace(/^```(\w*) *([^"\n]*).*\n([\s\S]*?)^```$/gm,
  (_, lang, label, code) => [`:::callout{type="listing" label="${label || lang}"}`,
    // One paragraph per line; a blank line keeps the word joiner alone.
    ...code.replace(/\n$/, '').split('\n').map((line) => codeLine(line, lang)), ':::',
  ].join('\n\n'));
// The text after a listing goes in :::paragraphs{style="resume"}: flush, as after a heading.
const resume = { id: 'resume', firstLineIndent: ZERO };
const listing = {
  id: 'listing', background: col('night'), span: 'page', // across the text and the margin
  padding: { top: mm(4), right: mm(5), bottom: mm(4), left: mm(5) },
  marginTop: mm(6), marginBottom: mm(2.5),
  label: { fontFamily: MONO, fontSize: pt(7), fontWeight: 700, color: col('phosphor'),
    background: col('night'), height: mm(5), offset: mm(5), paddingX: mm(3), // the tab
    position: 'top-left' },
  body: { fontFamily: MONO, fontSize: pt(8.6), lineHeight: pt(12.4), textAlign: 'left',
    color: col('code'), boldColor: col('amber'), italicColor: col('phosphor'), // paint()
    // One paragraph per line of code: no space between them, even if bodyText adds some.
    paragraphSpacing: false, firstLineIndent: ZERO },
};
// #endregion

// #region paint: keywords bold, strings italic, comments a chip with no box
const KEYWORDS = 'if|then|else|elif|fi|for|in|do|done|while|until|case|esac' // reserved words
  + '|set|echo|cd|export|local|read'; // builtins; programs such as mkdir and rsync stay plain
const TOKEN = new RegExp(`("(?:\\\\.|[^"\\\\])*"|'[^']*')` // a quoted string
  + `|((?:^|(?<=\\s))#.*$)|\\b(${KEYWORDS})\\b`, 'g'); // a comment, a keyword
function paint(line) {
  let out = '';
  let last = 0;
  for (const { 0: token, 1: string, 2: comment, index } of line.matchAll(TOKEN)) {
    out += escape(line.slice(last, index));
    if (string) out += `*${escape(string)}*`;
    else if (comment) out += `:chip[${chipText(comment)}]{style="rem"}`;
    else out += `**${token}**`;
    last = index + token.length;
  }
  return out + escape(line.slice(last));
}
// In a session, what you type after the prompt is bold; the shell's answer stays plain.
const session = (line) => line.startsWith('$ ') ? `\\$ **${escape(line.slice(2))}**` : escape(line);
// #endregion

// #region keycaps: keys, and inline code in the mono face, are chips
// Chips never break or stretch, so a line with keys puts all its slack in its word spaces;
// the breaker tries other breaks before a space passes 140 % (default 200 %). Inside a chip
// maths stays literal, so '$' needs no backslash there, but ']' does.
const spacing = { maxWordSpacing: 1.4 }; // spread into bodyText
const chipText = (text) => text.replace(/[*_^~`]/g, '\\$&').replace(/]/g, '\\]');
const inlineCode = (markdown) => markdown.replace(/(?<!\\)`([^`\n]+)`/g,
  (_, code) => `:chip[${chipText(code)}]{style="code"}`);
const bare = { backgroundEnabled: false, borderWidth: ZERO, paddingX: ZERO, gap: ZERO };
const chipStyles = [
  { id: 'key', fontFamily: MONO, fontSize: pt(7.8), bold: true, color: col('ink'),
    background: col('code'), borderColor: col('slate'), borderWidth: pt(0.6),
    borderRadius: pt(1.6), paddingX: em(0.45), paddingY: em(0.14), gap: em(0.3) },
  { id: 'code', fontFamily: MONO, fontSize: em(0.88), ...bare }, // `grep` in running text
  { id: 'rem', fontFamily: MONO, color: col('slate'), ...bare }, // a comment in a listing
];
// #endregion

// #region sheet: a two-column cheat sheet floated to the foot of its page
const sheet = { ...listing, id: 'sheet', label: undefined, placement: 'bottom',
  columnGap: mm(8), padding: { top: mm(5), right: mm(6), bottom: mm(5.5), left: mm(6) },
  titleStyle: { fontFamily: MONO, fontSize: pt(7.5), fontWeight: 700, gap: mm(3.5),
    color: col('phosphor'), textTransform: 'uppercase', letterSpacing: pt(1.5) },
  body: { ...listing.body, fontFamily: DISPLAY, fontSize: pt(8.4), lineHeight: pt(13) } };
// #endregion

const aside = { id: 'aside', span: 'side', backgroundEnabled: false, // notes in the margin
  stripe: { enabled: true, side: 'top', width: pt(2.5), color: col('ember') },
  padding: { top: mm(2.2), right: ZERO, bottom: ZERO, left: ZERO },
  titleStyle: { fontFamily: MONO, fontSize: pt(7.5), fontWeight: 700, color: col('ember'),
    textTransform: 'uppercase', letterSpacing: pt(1.2), gap: mm(1.2) },
  body: { fontFamily: TEXT, fontSize: pt(8.6), lineHeight: pt(12.5), textAlign: 'left',
    firstLineIndent: ZERO } };
const colophon = { ...aside, id: 'colophon', stripe: { enabled: false }, body: { ...aside.body,
  fontFamily: MONO, fontSize: pt(7.5), lineHeight: pt(10.5), color: col('muted'),
  italicColor: col('muted') } };

// #region steps: numbered steps on the grid, a prompt sign for a separator
const orderedLists = { fontFamily: DISPLAY, fontWeight: 800, color: col('ember'),
  gap: em(0.7), separator: '›', separatorGap: em(0.25), separatorFontFamily: MONO,
  separatorFontWeight: 700, separatorColor: col('muted'),
  marginTop: ZERO, marginBottom: ZERO }; // the default 1.5 em opens 5.3 mm above and below
// #endregion

const OUTER = 15; // mm: the outer margin; the running heads align to it
const text = (id, content, family, size, look, placement) => ({ kind: 'text', id, content,
  fontFamily: family, fontSize: pt(size), color: col('ink'), placement, ...look,
  align: 'left', overflow: 'wrap' }); // design text is centred and cut with '…' by default
const below = (id, y, width) => ({ anchor: { to: `#${id}`, edge: 'below' },
  offset: { x: ZERO, y: mm(y) }, size: { width } });
const opener = { enabled: true, slot: { elements: [
  text('kicker', '{attr.kicker}', MONO, 8, { fontWeight: 700, letterSpacing: pt(1.6),
    textTransform: 'uppercase', color: col('ember') },
  { anchor: { to: 'container', edge: 'top-left' }, offset: { x: ZERO, y: mm(4) } }),
  // Design lineHeights are multiples (gotcha: design-lineheight-multiple).
  text('title', '{titleText}', DISPLAY, 33, { fontWeight: 800, lineHeight: 1.04 },
    below('kicker', 3.5, mm(118))),
  text('lead', '{attr.lead}', TEXT, 12, { italic: true, lineHeight: 1.36 },
    below('title', 5, 'fill')),
] } };
const head = (id, content, parity, edge, x, extra = {}) => ({
  kind: 'text', id, content, parity, pages: 'body', fontFamily: MONO, fontSize: pt(7.5),
  letterSpacing: pt(1.1), textTransform: 'uppercase', color: col('muted'),
  placement: { anchor: { to: 'page', edge }, offset: { x: mm(x), y: mm(12) } }, ...extra,
});
const folio = { fontWeight: 700, color: col('ember') };

const config = () => ({ // a factory: the engine caches resolved configs per object
  locale: t({ en: 'en-us', es: 'es' }), // exact codes (gotcha: hyphenation-locales)
  colorPalette, chipStyles, orderedLists, paragraphStyles: [resume],
  calloutStyles: [listing, sheet, aside, colophon],
  // #region page: a text column and a margin column that only listings and notes enter
  page: { sizePreset: 'custom', width: mm(178), height: mm(229), margins: {
    top: mm(22), bottom: mm(21), left: mm(20), right: mm(OUTER), mirror: true } },
  layout: { layoutType: 'oneAndHalf', sideColumnPercent: 26, gutterWidth: mm(6),
    sideColumnRole: 'floats', sideColumnSide: 'outer' },
  // #endregion
  bodyText: { ...spacing, // keycaps
    fontFamily: TEXT, fontSize: pt(10), lineHeight: pt(LEAD), color: col('ink'),
    boldColor: col('ink'), italicColor: col('ink'), referenceColor: col('ink'),
    firstLineIndent: mm(4.5), indentAfterHeading: false,
    maxRuntTracking: 0, // tracking it cannot paint (gotcha: runt-tracking-unpainted)
  },
  headings: { fontFamily: DISPLAY, color: col('ink'), fontWeight: 800, levels: [
    // Restated: any headings object drops the H1 break (gotcha: headings-drop-h1-break).
    { level: 1, breakBefore: { enabled: true, parity: 'odd' }, advancedDesign: opener },
    { level: 2, fontSize: pt(13), lineHeight: pt(LEAD), marginTop: pt(LEAD), marginBottom: ZERO },
  ] },
  header: { elements: [
    head('verso-folio', '{pageNumber}', 'even', 'top-left', OUTER, folio),
    head('verso-title', '{title}', 'even', 'top-left', OUTER + 8),
    head('recto-title', '{chapterTitle}', 'odd', 'top-right', -(OUTER + 8)),
    head('recto-folio', '{pageNumber}', 'odd', 'top-right', -OUTER, folio),
  ] },
  footer: { elements: [head('drop-folio', '{pageNumber}', 'all', 'top', 0, {
    ...folio, pages: 'opener', // the opener has no running head: its folio drops to the foot
    placement: { anchor: { to: 'container', edge: 'top' }, offset: { x: ZERO, y: mm(9) } } })] },
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = `---
Mostra en Markdown · 118 línies · content.es.md
title: "La terminal, con calma"
subtitle: "Guía de bolsillo de la línea de comandos"
author: "Tove Ahlberg"
---

# Piezas que encajan {kicker="Capítulo 4" lead="Cómo la tubería encadena programas sencillos para hacerle preguntas a una carpeta."}

Cada programa de este capítulo hace una sola cosa. \`ls\` muestra los nombres de una carpeta, \`grep\` se queda con las líneas que coinciden con un patrón, \`sort\` las ordena y \`du\` dice cuánto ocupa un archivo en el disco. La tubería, el carácter \`|\`, pasa lo que imprime un programa al siguiente, de modo que puedes encadenarlos en una sola línea y leer la respuesta al final.

:::callout{type="aside" title="El indicador"}
En un Mac, zsh muestra \`%\` en vez de \`$\`.
:::

Pruébalo en una carpeta de fotos. En los listados, las líneas que empiezan por el signo del dólar son las que escribes tú, sin el dólar, y ejecutas con :chip[Intro]{style="key"}. Ese signo es el indicador, que el intérprete de órdenes (la *shell*) muestra cuando te espera. Las de debajo son su respuesta.

\`\`\`console Terminal
$ cd ~/fotos/2025
$ ls | grep -c 'JPG$'
268
$ ls | grep -v 'JPG$'
IMG_0413.MOV
IMG_0977.MOV
IMG_1502.PNG
$ du -sh *.MOV | sort -rh
812M    IMG_0977.MOV
455M    IMG_0413.MOV
\`\`\`

:::paragraphs{style="resume"}
\`grep -c\` cuenta las líneas que coinciden sin imprimirlas, y \`-v\` se queda con las demás. Las comillas simples entregan el patrón a \`grep\` tal cual; en él, \`$\` marca el final de la línea. El asterisco de la última orden lo expande el intérprete: antes de que \`du\` arranque, \`*.MOV\` ya se ha convertido en la lista de los archivos \`.MOV\`.
:::

:::callout{type="aside" title="En un Mac"}
:chip[Ctrl]{style="key"} es :chip[control]{style="key"}

:chip[Intro]{style="key"} es :chip[retorno]{style="key"}

Los atajos usan :chip[control]{style="key"}, no :chip[comando]{style="key"}.
:::

## Cuando una orden no termina

Tarde o temprano lanzarás una orden que no acaba. Si escribes \`grep JPG\` sin ningún archivo detrás, \`grep\` se queda esperando a que teclees las líneas en las que debe buscar. Para detenerla, mantén :chip[Ctrl]{style="key"} y pulsa :chip[C]{style="key"}; vuelve el indicador y no ha cambiado nada. Para cerrar la entrada como es debido, pulsa :chip[Ctrl]{style="key"} :chip[D]{style="key"} al principio de una línea vacía; \`grep\` lo entiende como el final de la entrada. :chip[Ctrl]{style="key"} :chip[C]{style="key"} también detiene un \`ping\`, que, si no, escribiría una línea por segundo hasta que cerraras la ventana.

El intérprete también te ahorra teclear. Pulsa :chip[Tab]{style="key"} después de las primeras letras del nombre de un archivo o una carpeta y el intérprete completa el resto; si encajan varios nombres, te los enseña (bash espera a un segundo :chip[Tab]{style="key"}). :chip[↑]{style="key"} recupera la última orden, y cada pulsación retrocede una más, así que una tubería con una errata se corrige en vez de volver a escribirse.

1. Escribe \`cd ~/fo\` y pulsa :chip[Tab]{style="key"} para completar el nombre de la carpeta, \`fotos/\`; luego añade \`2025\` y pulsa :chip[Intro]{style="key"}.
2. Pulsa :chip[↑]{style="key"} hasta que vuelva a la línea \`ls | grep -v 'JPG$'\`.
3. Mantén :chip[Ctrl]{style="key"} y pulsa :chip[A]{style="key"} para saltar al principio de la línea; luego :chip[Ctrl]{style="key"} :chip[E]{style="key"} te devuelve al final.
4. Añade \`| sort -r\` y pulsa :chip[Intro]{style="key"}. Los mismos nombres salen en orden inverso.

:::callout{type="sheet" title="Chuleta · bash y zsh"}
:::columns{count=2 breaks="8"}
**En la línea**

:chip[Ctrl]{style="key"} :chip[A]{style="key"} al principio de la línea

:chip[Ctrl]{style="key"} :chip[E]{style="key"} al final de la línea

:chip[Ctrl]{style="key"} :chip[W]{style="key"} corta la palabra anterior

:chip[Ctrl]{style="key"} :chip[K]{style="key"} corta hasta el final

:chip[Ctrl]{style="key"} :chip[Y]{style="key"} pega lo que cortaste

:chip[Ctrl]{style="key"} :chip[T]{style="key"} cambia dos letras de sitio

**Órdenes e historial**

:chip[Ctrl]{style="key"} :chip[R]{style="key"} busca en órdenes anteriores

:chip[Ctrl]{style="key"} :chip[P]{style="key"} la orden anterior

:chip[Ctrl]{style="key"} :chip[C]{style="key"} detiene la orden en curso

:chip[Ctrl]{style="key"} :chip[Z]{style="key"} la suspende; \`fg\` la reanuda

:chip[Ctrl]{style="key"} :chip[L]{style="key"} limpia la pantalla

:chip[Ctrl]{style="key"} :chip[D]{style="key"} cierra la sesión (línea vacía)
:::
:::

## Un guion para guardar

Las órdenes que escribes cada semana merecen un archivo. Este copia cada carpeta de \`~/trabajo\` en un disco externo, dentro de una carpeta nueva con la fecha del día. Guárdalo como \`copia.sh\` en tu carpeta personal.

\`\`\`bash copia.sh
#!/usr/bin/env bash
# Copia cada carpeta de ~/trabajo en el disco, bajo la fecha de hoy.
set -euo pipefail

src="$HOME/trabajo"
dest="/Volumes/Copias/$(date +%F)"

mkdir -p "$dest"
for dir in "$src"/*/; do
  name=$(basename "$dir")
  rsync -a "$dir" "$dest/$name/"
  echo "copiada: $name"
done
\`\`\`

:::callout{type="aside" title="Modo archivo"}
\`rsync -a\` copia también las subcarpetas y conserva las fechas y los permisos de cada archivo.
:::

:::paragraphs{style="resume"}
La primera línea, el *shebang*, indica con qué programa se ejecuta el archivo. \`set -euo pipefail\` detiene el guion en la primera orden que falla, así que nunca sigue adelante con media copia. \`$(date +%F)\` ejecuta \`date\` y coloca lo que imprime, por ejemplo 2026-09-26, dentro de la ruta. Las comillas alrededor de cada variable mantienen entera una carpeta llamada Declaración de la renta; sin ellas, el intérprete partiría el nombre por los espacios y \`rsync\` buscaría cuatro carpetas que no existen.
:::

Haz el archivo ejecutable con \`chmod +x copia.sh\`, una sola vez, y lánzalo con \`./copia.sh\`. En Linux, un disco externo suele aparecer dentro de \`/media\`, en una carpeta con tu nombre de usuario, así que cambia la línea de \`dest\` para que coincida.

:::callout{type="colophon"}
*La terminal, con calma* es un libro inventado para el Recetario de Postext. Compuesto en Charis SIL, Sora y JetBrains Mono (SIL OFL). Texto: original, CC BY 4.0.
:::

El capítulo 5 lleva \`grep\` a \`/var/log\`, la carpeta de los registros del sistema, donde una tubería de tres órdenes cuenta cuántos errores se anotaron cada día de la última semana.
`; // content.<lang>.md, inlined by the Cookbook
const source = inlineCode(listings(markdown)); // fences first: their backticks are escaped
const continuation = { pageIndexOffset: 48, pageNumbering: { startAt: 49 } }; // p. 49, a recto

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
const FONTS = { 'Charis SIL': ['400', '400i'], Sora: ['400', '700', '800'],
  'JetBrains Mono': ['400', '400i', '700'] };

// ─── 4 · Build & show ───────────────────────────────────────────────────────
await loadFonts(FONTS, markdown);
const build = () => buildDocument({ markdown: source, continuation }, config());
const doc = await buildWithFonts(build, markdown);
showPages(doc, { title: t({ en: 'The Shell, Gently', es: 'La terminal, con calma' }) });

Kit · core, fonts, viewer: igual a totes les receptes · 235 línies
// ─── Kit ── helpers shared by every Cookbook recipe · postext.dev/cookbook ─────

// ─── Kit · core v1 ── the same in every recipe · postext.dev/cookbook ─────────
function mm(value) { return { value, unit: 'mm' }; }
function pt(value) { return { value, unit: 'pt' }; }
function em(value) { return { value, unit: 'em' }; }
/** The sample language's string: t({ en: 'Figure', es: 'Figura' }). */
function t(strings) { return strings[LANG] ?? Object.values(strings)[0]; }
/** A file in this recipe's assets folder, served from the Postext repo by jsDelivr. */
function asset(file) { return `https://cdn.jsdelivr.net/gh/drnachio/postext@main/cookbook/${RECIPE}/assets/${file}`; }

// ─── Kit · fonts v1 ── the same in every recipe · postext.dev/cookbook ────────
// Postext measures text with the faces the browser has loaded, and caches the
// widths, so every face must be ready before the first build. Faces come from
// Fontsource: the same static files the PDF embeds, so screen and PDF agree.

/** faces = { 'Family Name': ['400', '400i', '700'] }. `text` is the sample:
 *  letters beyond Latin-1 (č, ł, ő…) also load the latin-ext files. With
 *  `optional`, a face Fontsource does not ship is skipped instead of failing.
 *  Resolves to the number of faces added. */
async function loadFonts(faces, text = '', { optional = false } = {}) {
  kitStatus('Loading fonts…');
  const ranges = {
    latin: 'U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,'
      + 'U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD',
    'latin-ext': 'U+0100-02BA,U+02BD-02C5,U+02C7-02CC,U+02CE-02D7,U+02DD-02FF,U+0304,U+0308,U+0329,'
      + 'U+1D00-1DBF,U+1E00-1E9F,U+1EF2-1EFF,U+2020,U+20A0-20AB,U+20AD-20C0,U+2113,U+2C60-2C7F,U+A720-A7FF',
  };
  const subsets = /[Ā-˿Ḁ-ỿ]/.test(text) ? ['latin', 'latin-ext'] : ['latin'];
  const jobs = [];
  let added = 0;
  for (const [family, specs] of Object.entries(faces)) {
    const id = fontsourceId(family);
    const meta = optional ? await fontsourceMeta(family) : null;
    for (const spec of new Set(specs)) {
      const weight = parseInt(spec, 10);
      const style = spec.endsWith('i') ? 'italic' : 'normal';
      if (hasFace(family, weight, style)) continue;
      if (optional && !(meta?.weights.includes(weight) && meta.styles.includes(style))) continue;
      for (const subset of subsets) {
        const url = `https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-${subset}-${weight}-${style}.woff2`;
        const face = new FontFace(family, `url(${url}) format('woff2')`,
          { weight: String(weight), style, unicodeRange: ranges[subset] });
        jobs.push(face.load().then((ready) => { document.fonts.add(ready); added++; }, () => {
          if (subset === 'latin' && !optional) throw new Error(`Fontsource has no ${family} ${weight} ${style}`);
        }));
      }
    }
  }
  await Promise.all(jobs).catch((error) => { kitFail(error); throw error; });
  return added;
}

/** Runs `build` (a buildDocument or buildBundle call) and checks the faces
 *  the pages use. A regular face missing from FONTS is loaded with a warning;
 *  bold and italic variants are loaded when the family ships them. Then the
 *  measurement caches are cleared and the build runs again. */
async function buildWithFonts(build, text = '') {
  const tried = new Set();
  for (let round = 0; round < 3; round++) {
    kitStatus('Laying out…');
    await new Promise(requestAnimationFrame);          // let the status paint first
    const result = await Promise.resolve().then(build).catch((error) => { kitFail(error); throw error; });
    const wanted = { base: {}, variants: {} };
    for (const { font, base } of [result].flat().flatMap(fontStringsOf)) {
      const { family, weight, style } = parseFont(font);
      const key = `${family}|${weight}|${style}`;
      if (tried.has(key) || hasFace(family, weight, style)) continue;
      tried.add(key);
      (wanted[base ? 'base' : 'variants'][family] ??= []).push(`${weight}${style === 'italic' ? 'i' : ''}`);
    }
    if (Object.keys(wanted.base).length) {
      console.warn(`[cookbook] FONTS does not list ${JSON.stringify(wanted.base)}: loading them.`);
    }
    const added = await loadFonts(wanted.base, text) + await loadFonts(wanted.variants, text, { optional: true });
    if (added === 0) return result;
    clearMeasurementCache();
  }
  throw new Error('The fonts did not settle after three builds.');
}

/** Every font string of the layout. `base` marks a block's own face; its
 *  bold, italic and bold-italic variants are listed whether or not used. */
function fontStringsOf(doc) {
  const found = new Map();
  const walk = (node) => {
    if (!node || typeof node !== 'object') return;
    if (Array.isArray(node)) { node.forEach(walk); return; }
    for (const [key, value] of Object.entries(node)) {
      if (typeof value === 'string' && /fontString$/i.test(key)) {
        found.set(value, found.get(value) || key === 'fontString');
      } else if (value && typeof value === 'object') walk(value);
    }
  };
  walk(doc.pages);
  walk(doc.blocks);
  return [...found].map(([font, base]) => ({ font, base }));
}

/** '700 37.5px Open Sans' / 'italic 400 13px "Source Serif 4"' → { family, weight, style }.
 *  A string with no weight ('95.8px Young Serif', from a design text) is 400. */
function parseFont(font) {
  const m = /^(?:(italic|oblique)\s+)?(?:small-caps\s+)?(?:(\d+|bold|normal)\s+)?[\d.]+px\s+(.+)$/.exec(font.trim());
  if (!m) throw new Error(`Unexpected font string: ${font}`);
  const weight = m[2] === 'bold' ? 700 : !m[2] || m[2] === 'normal' ? 400 : Number(m[2]);
  return { family: m[3].replace(/^["']|["']$/g, ''), weight, style: m[1] ? 'italic' : 'normal' };
}

/** True when a loaded FontFace covers exactly this family, weight and style
 *  (document.fonts.check() is also true for families nobody declared). */
function hasFace(family, weight, style) {
  for (const face of document.fonts) {
    if (face.status !== 'loaded' || face.style !== style) continue;
    if (face.family.replace(/^["']|["']$/g, '') !== family) continue;
    const [low, high = low] = face.weight.split(' ').map(Number);
    if (weight >= low && weight <= high) return true;
  }
  return false;
}

/** Fontsource's id for a family: 'Source Serif 4' → 'source-serif-4'. */
function fontsourceId(family) { return family.toLowerCase().replace(/\s+/g, '-'); }

/** The weights and styles a family ships ({ weights: [400, 700], styles: ['normal', 'italic'] }), or null. */
function fontsourceMeta(family) {
  fontsourceMeta.cache ??= new Map();
  const id = fontsourceId(family);
  if (!fontsourceMeta.cache.has(id)) {
    fontsourceMeta.cache.set(id, fetch(`https://api.fontsource.org/v1/fonts/${id}`)
      .then((res) => (res.ok ? res.json() : null), () => null));
  }
  return fontsourceMeta.cache.get(id);
}

// ─── Kit · viewer v1 ── the same in every recipe · postext.dev/cookbook ───────
/** Shows the pages as facing spreads on a dark desk: the first page is a
 *  recto on its own, then verso | recto pairs, as in a bound book. Pages
 *  are painted when they scroll near the screen. */
function showPages(docs, { title, width = 460 } = {}) {
  const root = viewer(title);
  const pages = [docs].flat().flatMap((doc) =>
    doc.pages.map((page) => ({ doc, page, n: (doc.pageIndexOffset ?? 0) + page.index })));
  const spreads = [];
  let verso = null;
  for (const p of pages) {
    if (p.n % 2 === 1) { if (verso) spreads.push([verso, null]); verso = p; }
    else { spreads.push([verso, p]); verso = null; }
  }
  if (verso) spreads.push([verso, null]);
  const density = Math.min(window.devicePixelRatio || 1, 2);
  showPages.painter?.disconnect();
  const painter = new IntersectionObserver((entries) => {
    for (const { isIntersecting, target } of entries) {
      if (!isIntersecting) continue;
      painter.unobserve(target);
      const { doc, page } = target.postext;
      renderPageToCanvas(page, doc, target, { scale: (width * density) / page.width });
    }
  }, { rootMargin: '800px' });
  showPages.painter = painter;
  root.replaceChildren(...spreads.map((pair) => {
    const spread = document.createElement('div');
    spread.className = 'pt-spread';
    for (const p of pair) {
      const figure = document.createElement('figure');
      if (p) {
        const label = p.page.pageLabel || String(p.n + 1);
        const canvas = document.createElement('canvas');
        canvas.postext = p;
        canvas.style.aspectRatio = `${p.page.width} / ${p.page.height}`;
        canvas.setAttribute('role', 'img');
        canvas.setAttribute('aria-label', `Page ${label}`);
        const folio = document.createElement('figcaption');
        folio.textContent = label;
        figure.append(canvas, folio);
        painter.observe(canvas);
      } else figure.className = 'pt-blank';
      spread.append(figure);
    }
    return spread;
  }));
  kitStatus(`${pages.length} ${pages.length === 1 ? 'page' : 'pages'}`);
  document.documentElement.dataset.postext = 'ready';
  return pages.length;
}

/** The desk, the bar and the error reporting, created once. */
function viewer(title) {
  if (!document.getElementById('pt-kit')) {
    document.head.insertAdjacentHTML('beforeend', `<style id="pt-kit">
      :root { color-scheme: dark; }
      body { margin: 0; background: #0e1014; color: #b9bcc4; font: 13px/1.45 system-ui, sans-serif; }
      #pt-bar { position: sticky; top: 0; z-index: 1; display: flex; flex-wrap: wrap; align-items: center;
        gap: 6px 16px; padding: 10px 16px; background: rgb(14 16 20 / .92); backdrop-filter: blur(6px);
        border-bottom: 1px solid #23262d; }
      #pt-bar strong { color: #f4f1ea; font-weight: 600; }
      #pt-actions { display: flex; gap: 12px; margin-left: auto; }
      #pt-actions a, #pt-actions button { color: #d8a21a; font: inherit; background: none; border: 0; padding: 0; cursor: pointer; }
      #pages { display: grid; justify-items: center; gap: 48px; padding: 32px 16px 72px; }
      .pt-spread { display: flex; }
      .pt-spread figure { margin: 0; width: min(460px, 44vw); }
      .pt-spread canvas { display: block; width: 100%; background: #fff;
        box-shadow: 0 1px 2px rgb(0 0 0 / .5), 0 22px 44px -16px rgb(0 0 0 / .8); }
      .pt-spread figure:first-child canvas { box-shadow: inset -14px 0 14px -14px rgb(0 0 0 / .18), 0 1px 2px rgb(0 0 0 / .5), 0 22px 44px -16px rgb(0 0 0 / .8); }
      .pt-spread figcaption { margin-top: 10px; text-align: center; font: 600 10px/1 system-ui, sans-serif;
        letter-spacing: .18em; text-transform: uppercase; color: #6c7079; }
      .pt-blank { visibility: hidden; }
      @media (max-width: 760px) {
        .pt-spread { flex-direction: column; gap: 32px; }
        .pt-spread figure { width: min(460px, 92vw); }
        .pt-blank { display: none; }
      }
    </style>`);
    document.body.insertAdjacentHTML('afterbegin',
      '<header id="pt-bar"><strong id="pt-title"></strong><span id="pt-status" role="status"></span><span id="pt-actions"></span></header>');
    document.getElementById('pt-title').textContent = document.title || 'Postext';
    addEventListener('error', (event) => kitFail(event.error ?? event.message));
    addEventListener('unhandledrejection', (event) => kitFail(event.reason));
  }
  if (title) document.getElementById('pt-title').textContent = title;
  return document.getElementById('pages')
    ?? document.body.appendChild(Object.assign(document.createElement('main'), { id: 'pages' }));
}

function kitStatus(text) {
  viewer();
  document.getElementById('pt-status').textContent = text;
}

function kitFail(error) {
  document.documentElement.dataset.postext = 'error';
  kitStatus(`Error: ${error?.message ?? error}`);
}

// ─── /Kit ───────────────────────────────────────────────────────────────────────