Tell the user to run the official Grok Build sign-in in their own terminal:
"$HOME/.local/share/multi-cli/bin/multi" login grok
This hands off to grok login, which opens the browser flow, or
grok login --device-auth on a headless host. Check /multi-usage first: it
reports whether a renewable login is already present, in which case no sign-in is
needed. Tell the user that they must relaunch Claude afterward to load the Grok
rows. Never accept, request, read, or print credentials in chat; native
credentials remain owned by grok.