Tool detects hidden duplicate React copies that cause hook errors

A new command-line tool called onecopy helps developers identify duplicate React installations that cause 'Invalid hook call' errors. The tool addresses a scenario where npm ls reports only one version, but linked libraries or workspaces actually load separate copies from different directories. It works by tracing the actual file resolution path from each importing package's real location, grouping results by physical directory. The tool outputs which copies are being used, by whom, and the likely cause, and can be integrated into CI checks.