Rock salt PbTe (Fm-3m), 8-atom conventional cell, a = 6.462 A at 300 K. Drag-free known-answer control structure for the Thermoelectrics API Seebeck route (phonon drag in PbTe is confined to low temperature, so measured S is the diffusive value BoltzTraP2 computes). Validation record (pymatgen + ASE, 2026-09-23): formula PbTe, 8 sites, density 8.2413 g/cm3 vs 8.164 handbook (the ~1% difference is the usual X-ray vs pycnometric density spread), space group Fm-3m recovered at symprec 0.01 and 0.1, min pair distance 3.231 A (a/2), full occupancies, round-trips through pymatgen and ASE. Written as P1 with explicit sites, same format as the corrected TiNiSn control.