Why Charge Comes in One Size: A Census of Quantization Mechanisms, and the Pair-Unity Entry

Electric charge comes in one size: every electron carries exactly -e, every proton exactly +e, and neutrality-of-matter experiments bound any mismatch at |q_p + q_e|/e at roughly 10^-21. This paper censuses the mechanism classes the literature offers for charge quantization, stating precisely what each derives, what each assumes, and what observation would kill it. Dirac monopole quantization derives quantization conditionally on an unobserved monopole. Grand-unified embedding derives quantization and the proton-electron equality conditionally on a simple unified group whose signature prediction, proton decay, is bounded at >10^34 years and unobserved. Anomaly cancellation CONSTRAINS charge ratios within a generation given the fermion content; it does not explain the quantum's size. Kaluza-Klein compactification derives quantization from momentum on a circle whose compact dimension is unobserved. Compact-U(1) and lattice arguments ASSUME quantization in the choice of a compact gauge group, while correctly locating where quantization lives. The sixth entry is the pair-unity derivation of Paper 29 (DOI 10.5281/zenodo.23768419): charge universality DERIVED from the one-field postulate, the exact equality |q_p| = |q_e| DERIVED conditionally on pair-unity, the pair's zero-sum, and charge conservation, with a falsifiable prediction of exactly zero residue at the neutrality-of-matter bound. No class in the census derives the value of e (NOT DERIVED, every shelf), and the pair-unity entry does not derive the mass ratio m_p/m_e (NOT DERIVED, Paper 29). The census's terminal position: charge quantization has no unconditional derivation in the literature; every deriving class is conditional on an unobserved premise.