Verifies that an array covers every t-way interaction, the certificate check for covering arrays, using compiled C code with optional 'OpenMP' threading. Supports uniform and mixed-level (per-column symbol counts) arrays. Missing values mark flexible ("don't care") entries, which contribute nothing to coverage, so a verified array remains covering however they are filled. Designed to be easy to embed in other packages: a single C file with a registered .Call entry point and one R wrapper.