Given a documentation URL, crawl the docs and produce a fast-onboarding brief — mental model, the core 20% of the API, beginner gotchas, a runnable spike, and a cheat sheet. Use when the user pastes a docs link and wants to "get up to speed", "learn this fast", "onboard", "give me the 20%", or otherwise asks for a quick practical overview of a library, framework, API, or tool from its documentation.