Add KDP cover PDF generator

scripts/cover.js computes the exact cover canvas dimensions from the
page count in book-meta.json (written by build.js), using the KDP
Premium Color spine formula (0.002347 in/page), and renders a
Nunjucks template to a single PDF containing back cover, spine, and
front cover with bleed (0.125 in) and safe-zone overlay guides.

- `pnpm cover`  — generate output/cover.pdf
- `pnpm all`    — build interior + both PDFs in one command
- Cover artwork slots: images/cover/front.png, images/cover/back.png

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/build.js

@@ -64,8 +64,14 @@ async function build() {
   const outPath = join(root, 'output', 'book.html');
   await writeFile(outPath, html, 'utf-8');
 
-  const pageCount = stories.reduce((acc, s) => acc + s.scenes.length * 2, 0) + 5;
-  console.log(`Built output/book.html — ${stories.length} stories, ~${pageCount} pages`);
+  // title page + copyright + TOC + (4 scenes × 2 pages per story) + finale
+  const pageCount = 3 + stories.reduce((acc, s) => acc + s.scenes.length * 2, 0) + 1;
+  await writeFile(
+    join(root, 'output', 'book-meta.json'),
+    JSON.stringify({ pageCount, storyCount: stories.length, builtAt: new Date().toISOString() }, null, 2),
+    'utf-8'
+  );
+  console.log(`Built output/book.html — ${stories.length} stories, ${pageCount} pages`);
 }
 
 build().catch(err => { console.error(err); process.exit(1); });

scripts/cover.js

@@ -0,0 +1,99 @@
+import puppeteer from 'puppeteer';
+import { readFile, writeFile, access } from 'fs/promises';
+import { resolve, dirname } from 'path';
+import { fileURLToPath } from 'url';
+import nunjucks from 'nunjucks';
+
+const __dir = dirname(fileURLToPath(import.meta.url));
+const root = resolve(__dir, '..');
+
+// KDP constants — Premium Color paper, 8.5×8.5 in trim
+const BLEED_IN        = 0.125;
+const TRIM_W_IN       = 8.5;
+const TRIM_H_IN       = 8.5;
+const SPINE_PER_PAGE  = 0.002347;   // inches per page, Premium Color
+const SAFE_IN         = 0.125;      // safe zone inset from trim edge (front/back)
+const SPINE_SAFE_IN   = 0.0625;     // safe zone inset from spine fold (each side)
+const MIN_SPINE_TEXT  = 79;         // KDP minimum pages for spine text
+
+async function fileExists(p) {
+  try { await access(p); return true; } catch { return false; }
+}
+
+async function generate() {
+  // Read page count produced by build.js
+  const metaPath = resolve(root, 'output', 'book-meta.json');
+  let pageCount = 100;
+
+  if (await fileExists(metaPath)) {
+    const meta = JSON.parse(await readFile(metaPath, 'utf-8'));
+    pageCount = meta.pageCount;
+    console.log(`Page count: ${pageCount}  (from output/book-meta.json)`);
+  } else {
+    console.warn(`book-meta.json not found — using default page count ${pageCount}`);
+    console.warn('Run `pnpm build` first for an accurate spine width.\n');
+  }
+
+  // Compute dimensions
+  const spineWidth  = pageCount * SPINE_PER_PAGE;
+  const totalWidth  = BLEED_IN + TRIM_W_IN + spineWidth + TRIM_W_IN + BLEED_IN;
+  const totalHeight = BLEED_IN + TRIM_H_IN + BLEED_IN;
+
+  console.log(`Spine width : ${spineWidth.toFixed(4)} in`);
+  console.log(`Cover canvas: ${totalWidth.toFixed(4)} × ${totalHeight.toFixed(4)} in\n`);
+
+  // Check for optional artwork files
+  const frontImage = await fileExists(resolve(root, 'images/cover/front.png'))
+    ? '../images/cover/front.png' : null;
+  const backImage  = await fileExists(resolve(root, 'images/cover/back.png'))
+    ? '../images/cover/back.png' : null;
+
+  // Render HTML from template
+  const env = nunjucks.configure(resolve(root, 'templates'), { autoescape: false });
+  const html = env.render('cover.html', {
+    pageCount,
+    spineWidth:   spineWidth.toFixed(4),
+    totalWidth:   totalWidth.toFixed(4),
+    totalHeight:  totalHeight.toFixed(4),
+    bleed:        BLEED_IN,
+    trimW:        TRIM_W_IN,
+    trimH:        TRIM_H_IN,
+    safe:         SAFE_IN,
+    spineSafe:    SPINE_SAFE_IN,
+    hasSpineText: pageCount >= MIN_SPINE_TEXT,
+    frontImage,
+    backImage,
+  });
+
+  const htmlOut = resolve(root, 'output', 'cover.html');
+  await writeFile(htmlOut, html, 'utf-8');
+
+  // Generate PDF
+  const systemChromium = '/usr/bin/chromium';
+  const useSystem = await fileExists(systemChromium);
+  console.log(`Launching Puppeteer (${useSystem ? 'system Chromium' : 'bundled Chrome'})…`);
+
+  const browser = await puppeteer.launch({
+    headless: true,
+    ...(useSystem ? { executablePath: systemChromium } : {}),
+  });
+
+  const page = await browser.newPage();
+  await page.goto(`file://${htmlOut}`, { waitUntil: 'networkidle0' });
+
+  const pdfOut = resolve(root, 'output', 'cover.pdf');
+  await page.pdf({
+    path: pdfOut,
+    width:  `${totalWidth}in`,
+    height: `${totalHeight}in`,
+    printBackground: true,
+    margin: { top: 0, bottom: 0, left: 0, right: 0 },
+  });
+
+  await browser.close();
+  console.log('Cover PDF written to output/cover.pdf');
+  console.log('\nNote: KDP recommends CMYK for covers. This PDF is RGB.');
+  console.log('Convert with Adobe Acrobat or Ghostscript before upload if needed.');
+}
+
+generate().catch(err => { console.error(err); process.exit(1); });