Spin-torsion source in unpolarized fermionic matter: net-number scaling and the vanishing of the Hehl-Datta term in pair-symmetric plasma

The Einstein-Cartan-Sciama-Kibble (ECSK) theory replaces the singularity of gravitational collapse with a bounce sourced by a spin-squared correction, but every standard estimate uses the Weyssenhoff spin fluid rather than the Dirac field the matter actually is. We evaluate the Hehl-Datta axial-axial four-fermion correction to the comoving energy density in the physically relevant unpolarized states, by canonical mode-sum Wick contraction, and verify the operator algebra against an exact 256-dimensional Fock-space computation that uses no Wick theorem. The correction is a perfect square in the net fermion distribution: it vanishes exactly in the chiral limit in pair-symmetric plasma and equals −3α(n−n̄)², with α = κ(ℏc)²/32, in degenerate matter at leading order — repulsive, three times the Weyssenhoff value. Torsion-bounce sourcing must therefore use net conserved fermion number, removing the torsion source from high-entropy early-universe cosmology while preserving it in low-entropy stellar collapse, and resolving Kerlick's 1975 sign question: attraction requires spin polarization. Acknowledgements: The derivations and numerical computations in this work were developed with AI assistance (Claude, Anthropic). All results were verified against exact finite-mode computations and independently executable scripts, archived as supplementary material.