Add Ghostscript post-processing to cover.js (CMYK + font embed + metadata)

Puppeteer writes cover-raw.pdf, Ghostscript converts RGB→CMYK via
-sColorConversionStrategy=CMYK -dProcessColorModel=/DeviceCMYK,
fully embeds fonts (-dPDFSETTINGS=/prepress), and injects title/author
metadata via UTF-16BE pdfmarks. Temp files are cleaned up on success.
Mirrors the same GS pipeline already used in pdf.js for the interior.

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

scripts/cover.js

@@ -1,10 +1,13 @@
 import puppeteer from 'puppeteer';
-import { readFile, writeFile, access } from 'fs/promises';
+import { readFile, writeFile, stat, rename, unlink, access } from 'fs/promises';
 import { resolve, dirname } from 'path';
 import { fileURLToPath } from 'url';
+import { execFile } from 'child_process';
+import { promisify } from 'util';
 import nunjucks from 'nunjucks';
 import matter from 'gray-matter';
 
+const execFileAsync = promisify(execFile);
 const __dir = dirname(fileURLToPath(import.meta.url));
 const root = resolve(__dir, '..');
 
@@ -21,6 +24,58 @@ async function fileExists(p) {
   try { await access(p); return true; } catch { return false; }
 }
 
+// Encode a JS string as UTF-16BE hex for PostScript pdfmarks (handles umlauts etc.)
+function toUtf16BeHex(str) {
+  const hex = [];
+  for (let i = 0; i < str.length; i++) {
+    const cp = str.charCodeAt(i);
+    hex.push(((cp >> 8) & 0xff).toString(16).padStart(2, '0'));
+    hex.push((cp & 0xff).toString(16).padStart(2, '0'));
+  }
+  return 'FEFF' + hex.join('').toUpperCase();
+}
+
+function buildPdfmarks({ title, author }) {
+  return [
+    '[ /Title <' + toUtf16BeHex(title)  + '>',
+    '  /Author <' + toUtf16BeHex(author) + '>',
+    '  /Creator (Puppeteer + Ghostscript)',
+    '  /DOCINFO pdfmark',
+  ].join('\n');
+}
+
+async function runGhostscript({ rawPath, outputPath, marksPath, title, author, totalWidth, totalHeight }) {
+  await writeFile(marksPath, buildPdfmarks({ title, author }), 'utf-8');
+
+  const args = [
+    '-dBATCH', '-dNOPAUSE', '-dQUIET',
+    '-sDEVICE=pdfwrite',
+    '-dCompatibilityLevel=1.4',
+    '-dPDFSETTINGS=/prepress',
+    '-dEmbedAllFonts=true',
+    '-dSubsetFonts=false',
+    '-dDownsampleColorImages=false',
+    '-dDownsampleGrayImages=false',
+    '-dDownsampleMonoImages=false',
+    // RGB → CMYK conversion
+    '-sColorConversionStrategy=CMYK',
+    '-dProcessColorModel=/DeviceCMYK',
+    `-sOutputFile=${outputPath}`,
+    marksPath,
+    rawPath,
+  ];
+
+  try {
+    await execFileAsync('gs', args);
+  } catch (err) {
+    console.error('Ghostscript failed:', err.message);
+    await rename(rawPath, outputPath);
+    console.warn('Falling back to raw Puppeteer PDF (RGB, no GS post-processing).');
+    return false;
+  }
+  return true;
+}
+
 async function generate() {
   // Read page count produced by build.js
   const metaPath = resolve(root, 'output', 'book-meta.json');
@@ -52,6 +107,8 @@ async function generate() {
   // Load author / title from front matter
   const fmRaw = await readFile(resolve(root, 'content', '00-front-matter.md'), 'utf-8');
   const { data: fm } = matter(fmRaw);
+  const title  = fm.title  || 'Das Kaleidoskop der Schlummerwelten';
+  const author = fm.author || '';
 
   // Render HTML from template
   const env = nunjucks.configure(resolve(root, 'templates'), { autoescape: false });
@@ -68,15 +125,19 @@ async function generate() {
     hasSpineText: pageCount >= MIN_SPINE_TEXT,
     frontImage,
     backImage,
-    author:   fm.author   || '',
-    title:    fm.title    || 'Das Kaleidoskop der Schlummerwelten',
+    author,
+    title,
     subtitle: fm.subtitle || '',
   });
 
   const htmlOut  = resolve(root, 'output', 'cover.html');
+  const rawPath  = resolve(root, 'output', 'cover-raw.pdf');
+  const marksPath = resolve(root, 'output', 'cover-pdfmarks.ps');
+  const pdfOut   = resolve(root, 'output', 'cover.pdf');
+
   await writeFile(htmlOut, html, 'utf-8');
 
-  // Generate PDF
+  // Generate raw PDF with Puppeteer
   const systemChromium = '/usr/bin/chromium';
   const useSystem = await fileExists(systemChromium);
   console.log(`Launching Puppeteer (${useSystem ? 'system Chromium' : 'bundled Chrome'})…`);
@@ -89,9 +150,8 @@ async function generate() {
   const page = await browser.newPage();
   await page.goto(`file://${htmlOut}`, { waitUntil: 'networkidle0' });
 
-  const pdfOut = resolve(root, 'output', 'cover.pdf');
   await page.pdf({
-    path: pdfOut,
+    path: rawPath,
     width:  `${totalWidth}in`,
     height: `${totalHeight}in`,
     printBackground: true,
@@ -99,9 +159,20 @@ async function generate() {
   });
 
   await browser.close();
+
+  const rawSize = (await stat(rawPath)).size;
+  console.log(`Raw PDF: ${(rawSize / 1_048_576).toFixed(1)} MB`);
+
+  console.log('Running Ghostscript (CMYK conversion + font embedding + metadata)…');
+  const gsOk = await runGhostscript({ rawPath, outputPath: pdfOut, marksPath, title, author, totalWidth, totalHeight });
+
+  if (gsOk) {
+    const finalSize = (await stat(pdfOut)).size;
+    console.log(`Final PDF: ${(finalSize / 1_048_576).toFixed(1)} MB  (CMYK)`);
+    await unlink(rawPath).catch(() => {});
+    await unlink(marksPath).catch(() => {});
     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); });