feat(monospace): EPUB export embeds TTF via --epub-embed-font + manifest patch

src/main/EpubFontEmbedder.js

@@ -0,0 +1,44 @@
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+const JSZip = require('jszip');
+
+// Patches an EPUB produced by pandoc so it embeds the supplied TTF font files
+// inside the OEBPS and registers them in the OPF manifest. Used after
+// `pandoc --epub-embed-font=...` runs (which embeds the font data) but does
+// not always add the manifest item we need for readers to discover the font.
+//
+// Writes a new file at `${epubPath}.patched.epub` and returns the patched path.
+// Caller should overwrite the original after a successful export.
+async function patchManifest(epubPath, fonts) {
+  const zip = await JSZip.loadAsync(fs.readFileSync(epubPath));
+  const opfPath = Object.keys(zip.files).find((f) => f.endsWith('content.opf'));
+  if (!opfPath) throw new Error('EPUB has no content.opf');
+  let opf = await zip.file(opfPath).async('string');
+
+  for (const { path: fontPath, family, weight } of fonts) {
+    const filename = path.basename(fontPath);
+    const inFontDir = `OEBPS/fonts/${filename}`;
+    zip.file(inFontDir, fs.readFileSync(fontPath));
+    if (!opf.includes(filename)) {
+      const safeFamily = String(family || 'Font').replace(/\s+/g, '-');
+      const item = `<item id="font-${safeFamily}-${weight}" href="${inFontDir}" media-type="application/x-font-ttf"/>`;
+      if (opf.includes('</manifest>')) {
+        opf = opf.replace('</manifest>', `${item}</manifest>`);
+      } else {
+        // OPF without a manifest element (unusual but tolerated): inject one
+        // just before </package> so the font item is still discoverable.
+        opf = opf.replace('</package>', `<manifest>${item}</manifest></package>`);
+      }
+    }
+  }
+
+  zip.file(opfPath, opf);
+  const buf = await zip.generateAsync({ type: 'nodebuffer' });
+  const tmp = `${epubPath}.patched.epub`;
+  fs.writeFileSync(tmp, buf);
+  return tmp;
+}
+
+module.exports = { patchManifest };