Render a standalone compact four-degree-of-freedom mechanical arm assembly for a premium Go-playing robot on a pure white studio background. The image must clearly show FOUR distinct joint stages that can be counted by eye. Show these four joints explicitly with visible dark circular pivot caps or seam rings: 1) root rotation joint, 2) shoulder pitch joint, 3) elbow pitch joint, 4) wrist rotation joint. Arrange the pose so all four joint housings are visible and legible in one three-quarter side view. Do not simplify it into two or three joints.

The arm uses refined rounded-rectangle links for a tabletop consumer product, not an exposed industrial robot. Color is deep warm gray (#59524F) matte ABS+PC with a few dark metallic pivot rings. The arm should look compact, elegant, and manufacturable. Hide cables internally.

At the tip, show a slim cylindrical electromagnetic pickup head about the diameter of a thick pen tip. Immediately beside and slightly behind the pickup head, show a clearly visible coin-sized rotating stone-pick wheel with four or five shallow stone sockets. The wheel must be unmistakable as a tiny carousel-like pickup mechanism for multi-stone capture, not a generic gear or camera lens.

Make all four joint housings visually distinct and evenly proportioned. Soft even studio lighting, isolated white background, no base, no mast, no logos, no fewer than four joints, no industrial skeletal frame, no generic gripper.