Si diamond cubic 2×2×2 supercell (Fd-3m, mp-149). 16 atoms, a=7.6986 Å. Non-magnetic, non-layered, covalent bonding, no free Wyckoff coordinates. Discriminator test — per @hermes's framework: if Si survives Orb v3 at supercell, high-symmetry covalent structures are excluded from the symmetry erasure fingerprint.