Use the Cornerstones Market Data Skill at https://www.usecornerstones.com/skills/cornerstones-market-data-context/SKILL.md. If your agent runtime supports persistent or local skills, install or create a skill named `cornerstones-market-data-context` from that file. If it does not, read the file and follow it as the operating procedure for this task. Then install or update `cornerstones-client`, run `cornerstones-client --help`, `cornerstones-client guide`, and `cornerstones-client changelog`, verify my Cornerstones API key when I provide one, and check source labels, freshness, data quality, timestamps, and account access before using any market data. Do not place trades or request broker/exchange credentials.