feat(monospace): add xelatex fontspec header builder

tests/unit/main/monospace/PdfFontHeader.test.js

@@ -0,0 +1,64 @@
+const fs = require('fs');
+const path = require('path');
+const os = require('os');
+
+const { buildPdfFontHeader } = require('../../../../src/main/PdfFontHeader');
+
+describe('PdfFontHeader', () => {
+  let tmpDir;
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'mono-pdfhdr-'));
+  });
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  test('writes a fontspec header for JetBrains Mono Regular', () => {
+    const ttf = path.join(tmpDir, 'JetBrainsMono-Regular.ttf');
+    fs.writeFileSync(ttf, 'fake');
+    const out = buildPdfFontHeader(
+      { monospaceFont: 'jetbrains-mono', monospaceLigatures: false },
+      ttf,
+      'JetBrains Mono'
+    );
+    expect(typeof out.headerPath).toBe('string');
+    expect(fs.existsSync(out.headerPath)).toBe(true);
+    const content = fs.readFileSync(out.headerPath, 'utf-8');
+    expect(content).toContain('\\setmonofont');
+    expect(content).toContain('JetBrainsMono-Regular.ttf');
+    expect(out.familyName).toBe('JetBrains Mono');
+  });
+
+  test('writes header with ligatures when enabled', () => {
+    const ttf = path.join(tmpDir, 'FiraCode-Regular.ttf');
+    fs.writeFileSync(ttf, 'fake');
+    const out = buildPdfFontHeader(
+      { monospaceFont: 'fira-code', monospaceLigatures: true },
+      ttf,
+      'Fira Code'
+    );
+    const content = fs.readFileSync(out.headerPath, 'utf-8');
+    expect(content).toContain('Ligatures=TeX');
+  });
+
+  test('header is written under os.tmpdir', () => {
+    const ttf = path.join(tmpDir, 'JetBrainsMono-Regular.ttf');
+    fs.writeFileSync(ttf, 'fake');
+    const out = buildPdfFontHeader(
+      { monospaceFont: 'jetbrains-mono', monospaceLigatures: false },
+      ttf,
+      'JetBrains Mono'
+    );
+    expect(out.headerPath.startsWith(os.tmpdir())).toBe(true);
+  });
+
+  test('throws if ttfPath does not exist', () => {
+    expect(() =>
+      buildPdfFontHeader(
+        { monospaceFont: 'jetbrains-mono', monospaceLigatures: false },
+        '/nonexistent.ttf',
+        'JetBrains Mono'
+      )
+    ).toThrow(/TTF/);
+  });
+});