Exporting the map to an image throws 'canvas tainted'

• `Uncaught DOMException: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.`
• html2canvas produces a fully white basemap while page text and buttons render normally
• A test `Image` with `crossOrigin = 'anonymous'` fires `onerror` for the tile URL

1. Check the tile response for an `access-control-allow-origin` header
2. Look for an `Origin` request header to confirm the request was a CORS request
3. Load one tile into an `Image` with `crossOrigin='anonymous'` and watch `onload` versus `onerror`
4. Confirm the export region contains no third-party images such as external icons in popups
5. Decide between adding CORS headers and proxying same-origin

Set `crossOrigin: 'anonymous'` on the tile layer and add `Access-Control-Allow-Origin` for your site on the server, since both conditions are required; when the tile host cannot be changed, proxy it under your own domain and add the header there.

Uncaught DOMException: Failed to execute 'toDataURL' on 'HTMLCanvasElement':
Tainted canvases may not be exported.

const img = new Image();
img.crossOrigin = 'anonymous';
img.onload = () => console.log('可导出');
img.onerror = () => console.log('CORS 未通过，服务端缺少响应头');
img.src = 'https://tile.example.com/10/843/392.png';

• Setting `crossOrigin` without server-side CORS, so the tiles fail to load and the map becomes grey blocks
• Blaming the map canvas when a third-party logo image inside a popup is the actual tainting source