Shell (Shift+H) — VMK's first Fusion-flavored op. Select faces in face mode, Shift+H, and they become the openings: the rest of the component hollows into a uniform wall. Drag for thickness or type an exact value in mm; LMB/Enter confirms, ESC cancels clean through the topology undo. The fun part: the hard math was already on the shelf. The even-thickness vertex normals the outline pass uses (angle-weighted face normals scaled by 1/avg_cos) are exactly the offset vectors a shell needs — move t along one and you land precisely t off every adjacent face plane. So a 2-unit wall on the cube pulls corners (2,2,2) and opening-rim verts (2,2,0), exact to the float. Inner skin winds reversed to front the cavity, boundary edges get rim quads, multi-face and multi-opening selections all work (two opposite faces → open tube). One-shot O(component) topology op: zero per-frame cost, nothing outside GLES2, Pi-safe by construction. REPL grew a matching `shell [thickness]` command and test_19 locks in counts, exact wall positions, undo round-trips, and the L-shaped shared-edge opening case. 15/15 green.