uutils/coreutils ? reverse-engineered prompt

Build me a cross platform Rust version of the GNU core utilities that works like the real thing as closely as possible.

I want one command line tool, or a set of utilities, that covers the usual core commands people expect from GNU coreutils, with the same outputs and exit codes wherever you can match them. If there are small differences from GNU, treat them like bugs and keep improving them. It should work on Linux, macOS, BSD, Windows, and ideally WASI too, so scripts can move between systems more easily.

Please include a fast build and install flow, support for a BusyBox style multicall binary, and the option to build individual utilities too. Make sure the project has good tests, clear error messages, and basic docs for building and using it. If you need current details on any command behavior or platform quirks, look up the latest docs online and follow the upstream GNU behavior as much as possible.