Robust URL-to-Markdown extraction for OpenClaw workflows. Use when the user wants to extract, summarize, or convert a webpage to Markdown (especially WeChat mp.weixin.qq.com) and web_fetch/browser is blocked or messy. Employs a cost-effective probe via web_fetch initially, then falls back to the official MinerU API (via the local mineru-extract skill), returning a traceable result contract with source links.