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

src/main.js

@@ -9,6 +9,7 @@ const GitOperations = require('./main/GitOperations');
 const PdfFontHeader = require('./main/PdfFontHeader');
 const MonospaceFontConfig = require('./main/MonospaceFontConfig');
 const ExportCss = require('./main/ExportCss');
+const EpubFontEmbedder = require('./main/EpubFontEmbedder');
 
 // Add MiKTeX to PATH for LaTeX support
 if (process.platform === 'win32') {
@@ -2838,6 +2839,45 @@ function performExportWithOptions(format, options) {
       } else if (format === 'confluence' || format === 'jira') {
         pandocCmd = `${getPandocPath()} "${currentFile}" -t jira -o "${outputFile}"`;
         exportWithPandoc(pandocCmd, outputFile, format);
+      } else if (format === 'epub') {
+        // Embed the active monospace TTF into EPUB so code blocks render in
+        // JetBrains Mono / Fira Code regardless of the reader's installed fonts.
+        if (pandocSupportsEpubEmbedFont()) {
+          const familyKey = readSettingsJsonCached().monospaceFont || 'jetbrains-mono';
+          const regular = MonospaceFontConfig.getMonoFontTtfPath(familyKey, 400);
+          const bold = MonospaceFontConfig.getMonoFontTtfPath(familyKey, 700);
+          [regular, bold].filter(Boolean).forEach((p) => {
+            pandocCmd += ` --epub-embed-font="${p}"`;
+          });
+        }
+        runPandocCmd(pandocCmd, async (error) => {
+          if (error) {
+            dialog.showErrorBox(
+              'Export Error',
+              sanitizeErrorMessage(`Failed to export EPUB: ${error.message}`)
+            );
+            return;
+          }
+          // Patch the OPF manifest so readers can locate the embedded font.
+          // Skip silently if the file is missing or pandoc didn't embed.
+          try {
+            const familyKey = readSettingsJsonCached().monospaceFont || 'jetbrains-mono';
+            const regular = MonospaceFontConfig.getMonoFontTtfPath(familyKey, 400);
+            const fonts = [];
+            if (regular) fonts.push({ path: regular, family: familyKey === 'fira-code' ? 'Fira Code' : 'JetBrains Mono', weight: 400 });
+            if (fonts.length) {
+              const patched = await EpubFontEmbedder.patchManifest(outputFile, fonts);
+              try {
+                fs.renameSync(patched, outputFile);
+              } catch (renameErr) {
+                if (typeof console !== 'undefined') console.warn('[epub] could not overwrite with patched EPUB:', renameErr.message);
+              }
+            }
+          } catch (patchErr) {
+            if (typeof console !== 'undefined') console.warn('[epub] manifest patch failed:', patchErr.message);
+          }
+          showExportSuccess(outputFile);
+        });
       } else if (format === 'mobi') {
         // First export to EPUB, then try ebook-convert if available
         const epubFile = outputFile.replace(/\.mobi$/i, '.epub');

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 };