Paper CCLV: Maximal CP Violation from the Cayley-Dickson Doubling Phase — δ_CP = −π/2 in the OOB PMNS Matrix

Derives the PMNS leptonic CP-violating phase δ_CP from framework primitives with zero free parameters. The Cayley-Dickson construction O = H × H (Paper L) introduces the new imaginary direction e₇ — identified as the brane-bulk separator under CXLIX — via a doubling phase that is exactly π/2 (the structural 'i' factor of the doubling step). The W boson, which lives in 5D effective phase space (Paper CCLIV) and mediates the (1,3) PMNS channel, carries this π/2 phase into the lepton mixing matrix. Combined with CCLII's negative G₂ tilt (which fixes the sign), the framework prediction is δ_CP = −π/2 = −90.00° = −1.5708 rad. This is maximal CP violation: |sin δ_CP| = 1, saturating the experimental upper bound on the Jarlskog invariant |J| ≤ 0.034 (predicted: |J| = 0.0333). The current T2K + NOvA combined best fit (NuFIT 6.x, 2024–2025) is δ_CP ≈ −1.50 ± 0.40 rad, placing the framework prediction at 0.18σ from the central value. CCLV closes the last open item of the OOB neutrino sector: with CCLII (Δm² ratio + PMNS angles), CCLIII (absolute scale), CCLIV (W-mediation unification), and CCLV (δ_CP magnitude), every PMNS observable follows from framework primitives at zero free parameters. Sharp falsification at DUNE + Hyper-K (~2030). Part of the One-Octonion Brane-Bulk Framework series. Anchor DOI: 10.5281/zenodo.19120873. Community: one-octonion-brane-bulk. Author: Bharathi Dasan Jagadeesan, M.D., University of Minnesota. ORCID: 0000-0002-1143-941X.