When USER_GOOGLE_EMAIL environment variable is set, include it in the MCP server instructions so that AI clients know which email to use for Google Workspace tools without asking the user. This improves the experience for desktop apps that handle OAuth externally and pass credentials via GOOGLE_MCP_CREDENTIALS_DIR + USER_GOOGLE_EMAIL. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>