Bell Factorization from Projective Phase Structure: Classical Recovery, CHSH Obstruction, No-Signaling, and Tsirelson Saturation

This paper proves a finite-dimensional structural recovery-and-obstruction theorem for Bell-local factorization inside projective phase structure. The primitive object is a completion-locked projective probability datum: a bipartite state, fixed local projective contexts, the Born–Haar reduction rule, and fixed normalization. A projective measurement context carries a compact relative phase torus, and Haar averaging over that torus gives the nonselective Born/Lüders projection channel. The Born probability table is therefore determined before any hidden-variable or Bell-local representation is tested. Bell-local factorization is determined as a derived classical recovery representation of the locked Born table. The paper proves canonical recovery regimes: pure product rays are exactly Segre-factorized projective phase classes, mixed separability yields Bell-local recovery, and one-sided commutative local readout pairs yield Bell-local recovery through a joint-outcome hidden variable. Conversely, a Clauser–Horne–Shimony–Holt (CHSH) value larger than 2 proves obstruction: no Bell-local representation exists for the chosen datum. No-signaling follows from the trace identities of the projective Born law, while Tsirelson’s bound 2√2 follows from the operator geometry of admissible binary projective observables. The theorem chain therefore determines the hierarchy: projective phase carrier → Born–Haar reduction → Segre/separable recovery or Bell-factorization obstruction → no-signaling and Tsirelson admissibility. This hierarchy also determines the intermediate cases: Bell–CHSH violation is a property of the complete projective measurement datum, not of entanglement alone. Product states, separable mixtures, commutative readouts, and nonoptimal settings can remain below the classical threshold even inside quantum theory. The constructive spin instantiation is derived explicitly. For the diagonal SU(2) action on ℂ² ⊗ ℂ², rotational invariance selects the unique spin-zero singlet line. The singlet is entangled by failure of Segre factorization, its Pauli spin correlations satisfy E(a,b) = −a·b, and optimal admissible spin readouts attain the exact Tsirelson value 2√2. In this derivation, 2√2 is not introduced by experiment-fitting; it is the Hilbert-space admissibility ceiling of the projective phase datum, realized exactly by the spin-zero SU(2) sector. License note: Distributed under CC BY-NC-ND 4.0.