  * fail early if a rust-*-dev package does not match contained crates
    * each contained crate must match a provided virtual fullname package
    * each virtual fullname package names must match a contained crate
  * resolve ${Cargo:Provides}
    * features
    * secondary crates
      resolved from comma-separated entries i X-Cargo-Crates: field
  * Optionally force use of wrapper
    * affects helvum
