DeepSeek Harness Web Search Plugin: Source-Traceable Brave / Tavily Search and Extraction

The DeepSeek Harness web search plugin packages the real-time search and URL extraction capabilities of Brave and Tavily into a native plugin. It provides a transparent and traceable search experience, with tools such as `web_search`, `web_extract`, `provider_status`, and `health_check`. At installation, API keys must be configured via environment variables. The plugin reads keys only from the environment and does not write them to configuration files, aiming to provide stable tool contracts and source traces for research workflows.