Fetches, harmonizes, and analyses data from the Spanish National Forest Inventory for reproducible, design-aware forest inventory workflows. Computes tree- and stand-level metrics, applies sampling-based expansion factors, estimates volume, and supports extensible processing for external inventory designs with custom sampling schemes and volume equations. Spatial extensions can attach plot geometries, preserve geometry sidecars through metric workflows, and return georeferenced sf outputs for mapping and remote-sensing integration.