feat(editor): migrate typst mermaid to native (#14499)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Native/WASM Mermaid and Typst SVG preview rendering on desktop and
mobile, plus cross-platform Preview plugin integrations.

* **Improvements**
* Centralized, sanitized rendering bridge with automatic Typst
font-directory handling and configurable native renderer selection.
* More consistent and robust error serialization and worker-backed
preview flows for improved stability and performance.

* **Tests**
* Extensive unit and integration tests for preview rendering, font
discovery, sanitization, and error serialization.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/apps/electron/test/helper/preview.spec.ts

@@ -0,0 +1,85 @@
+import path from 'node:path';
+
+import fs from 'fs-extra';
+import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
+
+const { native } = vi.hoisted(() => ({
+  native: {
+    renderMermaidSvg: vi.fn(),
+    renderTypstSvg: vi.fn(),
+  },
+}));
+
+vi.mock('@affine/native', () => native);
+
+const tmpDir = path.join(__dirname, 'tmp');
+const typstFontDirA = path.join(tmpDir, 'fonts-a');
+const typstFontDirB = path.join(tmpDir, 'fonts-b');
+
+async function loadPreviewHandlers() {
+  vi.resetModules();
+  const module = await import('../../src/helper/preview');
+  return module.previewHandlers;
+}
+
+describe('helper preview handlers', () => {
+  beforeEach(async () => {
+    await fs.ensureDir(typstFontDirA);
+    await fs.ensureDir(typstFontDirB);
+    process.env.AFFINE_TYPST_FONT_DIRS = [
+      typstFontDirA,
+      typstFontDirB,
+      path.join(tmpDir, 'missing'),
+    ].join(path.delimiter);
+    native.renderMermaidSvg.mockReset();
+    native.renderTypstSvg.mockReset();
+    native.renderMermaidSvg.mockReturnValue({
+      svg: '<svg><text>mermaid</text></svg>',
+    });
+    native.renderTypstSvg.mockReturnValue({
+      svg: '<svg><text>typst</text></svg>',
+    });
+  });
+
+  afterEach(async () => {
+    delete process.env.AFFINE_TYPST_FONT_DIRS;
+    await fs.remove(tmpDir);
+  });
+
+  test('passes mermaid request to native renderer', async () => {
+    const previewHandlers = await loadPreviewHandlers();
+    const request = { code: 'flowchart TD; A-->B' };
+
+    await previewHandlers.renderMermaidSvg(request);
+
+    expect(native.renderMermaidSvg).toHaveBeenCalledWith(request);
+  });
+
+  test('injects resolved fontDirs into typst requests', async () => {
+    const previewHandlers = await loadPreviewHandlers();
+
+    await previewHandlers.renderTypstSvg({ code: '= hello' });
+
+    const [request] = native.renderTypstSvg.mock.calls[0];
+    expect(request.options?.fontDirs).toEqual(
+      expect.arrayContaining([
+        path.resolve(typstFontDirA),
+        path.resolve(typstFontDirB),
+      ])
+    );
+  });
+
+  test('keeps explicit typst fontDirs', async () => {
+    const previewHandlers = await loadPreviewHandlers();
+    const request = {
+      code: '= hello',
+      options: {
+        fontDirs: ['/tmp/custom-fonts'],
+      },
+    };
+
+    await previewHandlers.renderTypstSvg(request);
+
+    expect(native.renderTypstSvg).toHaveBeenCalledWith(request);
+  });
+});