Function dispatch 

pub fn dispatch(argv: &[String]) -> u8

Dispatch a single argv invocation. Takes the full argv including argv[0]. Returns the exit code the binary should pass to std::process::exit.

All I/O goes through stdout/stderr so integration tests either spawn the binary (full end-to-end) or drive this entry point directly (in-process, faster). We keep this function small and dispatch-only so the command modules remain easy to snapshot.