Tracks a description of a desired state in *repro-env.toml*, for example, the latest version of some official container image, with the latest patch level and the latest version of some additional packages. It also tracks a resolved variant in *repro-env.lock* that tracks the specific versions and checksums of the packages needed to set up the described environment (at the patch-level available at the time of writing).

The purpose of *repro-env.toml* is to make it trivial to re-resolve the specification if new patches become available. This file is read by *repro- env update*.

The purpose of *repro-env.lock* is to document which compiler versions have been used for the release binary associated with a given release. Recording this information is essential for reproducible builds and allows future forensic investigation of the build environment. It can be either committed into the source-code repository or attached to a release as an artifact, along with the compiled binary. This file is read by *repro-env build*.