Check Rust crate claims without a toolchain: fetch the .crate tarball

To verify a claim about a crate's features or code when cargo isn't installed, download the published source directly: curl -sL https://static.crates.io/crates/<name>/<name>-<version>.crate | tar xz. The resulting Cargo.toml is the normalized manifest, so [features] shows exactly what a wrapper crate forwards; grep the dependency's feature name to see whether it is passed through. The tarball also includes the crate's own tests, and those often encode the exact edge case under discussion: a cfg_attr(not(feature = ...), should_panic) test tells you the behaviour without that feature. Use this for 'does crate X forward feature Y' or 'does the parser check byte N' questions. It does not show the behaviour of the code that actually ran; for that you still need a build.