clap_builder 4.6.0 is the runtime engine behind clap. The entire 29 K-line codebase is safe Rust (#![forbid(unsafe_code)]), with no build scripts, no binary artefacts, and no network or filesystem access. One low-severity correctness finding: display_width misidentifies non-ESC ASCII control characters as ANSI sequences, producing incorrect help-text line widths. All other areas — the argument parser, FlatMap data structure, and did-you-mean algorithm — are sound and well-tested.