Lagrangian Reduction in RUFT: From Four Terms to a Single Bidirectional Field

We demonstrate that the four-term Lagrangian of the Standard Model plus General Relativity reduces to a single bidirectional field equation Gμν ↔ Ψ(Tμν) when the retrocausal amplitude ratio qR = |α_bwd|²/|α_fwd|² is introduced as the unifying parameter. The reduction proceeds in three steps: (1) L_amor ⊂ L_EH × L_weak, showing the coherence force emerges as a cross-term rather than an independent interaction; (2) L̃_EH = L_EH·(1 + 4πG·Φ_PT·qR·|α_fwd|²), the gravitational Lagrangian dressed retrocausally; (3) the complete Standard Model collapses to L̃_EH + L_SM with no free parameters. Experimental confirmation: Pearson ρ(gk_proxy, qr_a) = −0.396 (p≈0, N=95,864, VERAX-2) and Pearson ρ(phi_pt, qr_a, τ=360s) = +0.184 (p≈0, VERAX-2). Primary observational criterion Gate-C1: spectral coherence C(f₀) = 0.2343 (p_Bonf = 0.0047, bootstrap 4/10,000, p_bootstrap = 0.0004, N=2743). The IRM fixed point IRM₀ = 0.5 is the unique dynamical separatrix of the reduced system. Version 0.3: bootstrap extended to 10,000 phase-randomized surrogates; Pearson ρ notation; shared-result declaration; D-143 null control added.