Vendored truck-stepio (writer only): an intersection curve's second surface was written at the first one's id (duplicate ids for every boolean edge), and revolved surfaces lost their orientation (the modeling-surface sense was always true; inverted or mirrored revolutions came out inside out). Export now writes intersection edges as C1 cubic B-splines through exact points, so files carry plain 3D curves and no redundant surfaces. Vendored truck-meshalgo: hinted parameter searches that run off a B-spline's domain are rejected or clamped (meshing their grid never finished). STEP import: straight revolution profiles are bounded in the meridian plane and stop at the axis; loops on revolutions start away from the axis; face extents include edge end points. Edges between pieces of one split surface draw as seams. kernel::step_validate checks a STEP file (duplicate ids, dangling references, dense numbering); the oracle replay now exports every rebuilt part, validates it and re-imports it with no warnings and the same volume (all 32 rebuildable cases pass). Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL