1. A computer-aided design (CAD) system, comprising: a computing device comprising a processor configured to execute: a parametric geometry engine configured for creating a historic instruction list of feature-based geometry of a CAD object such that modification of an earlier-created feature in the instruction list causes the parametric geometry engine to recalculate later-created geometric features to carry through the effects of the change to the earlier-created feature; a parametric modeling user interface configured for creating a history-dependent parametric feature constraint of the CAD object corresponding to the historic instruction list; and a direct modeling user interface for modifying the CAD object based on added geometry features agnostic of all associative geometric relationships within the CAD object, wherein the parametric geometry engine is configured to enforce the feature constraint in the direct modeling user interface, responsive to an attempt to modify the geometry via the direct modeling user interface, wherein the parametric geometry engine is configured to prevent or reject the attempt to modify the CAD object, responsive to the attempt to modify the geometry, and wherein the parametric geometry engine is configured to allow the user to override or modify the feature constraint in the direct modeling user interface.