STL repair

Repair common STL file issues without over-promising the result.

Run a mesh check first, apply safe repairs only where they are supported, and keep complex geometry visible in the repair report.

Safe repair candidates include degenerate faces, duplicate faces, and basic normal direction mismatches after fixture validation.

Complex non-manifold geometry, self-intersections, and thin walls are reported clearly instead of being forced into risky automatic edits.

Paid repaired STL downloads are designed to be generated and authorized server-side, not hidden behind a front-end button only.

Every V1 repair action must pass the repair feasibility gate before it becomes a normal export path.