Dunno how it'll work with Claude Code, but I use the context7 MCP to feed up-to-date docs in copilot.

Sometimes that also doesn't work so I make a guiding document using whatever llms.txt the framework/language/platform offers or just wget the entire documentation, condense it into a single text file and use that while prompting.

Seems to work ok, especially for Svelte 5 where most LLMs except Gemini don't give me runes from the get-go.