Worked on stabilizing the core raycasting logic in the mrdoob/three.js repository by addressing a specific edge case in the Ray.intersectSphere method. Applied JavaScript and mathematics skills to introduce a guard clause that correctly handles spheres with negative radii, preventing false intersections and reducing rendering glitches in geometry processing. Enhanced reliability by adding a targeted unit test to ensure that the method does not intersect with invalid spheres and that the target vector remains unchanged. This focused bug fix improved test coverage for edge-case geometry, supporting developers who rely on accurate ray-sphere intersection in complex three.js scenes and applications.