CDN-261 — The Formal Derivation (GCFT Art Edition)

Tests three candidate Lagrangians (Yukawa, Chameleon, acceleration-coupled) for deriving the CDN-258 coherence coupling κ(a). All fail: standard scalar fields couple to density (∇²Φ), but empirical κ(a) requires coupling to acceleration (|∇Φ|), demanding a disformal Lagrangian. Resolves D10: the apparent γ discrepancy between inter-system (1.10) and intra-system (~0.5) is a log-log curvature effect of the same functional form. Non-locality test negative: field-averaged κ worsens fit by +12.3 km/s RMS. Opens D11: derive S(a) from coherence microphysics.