The Causal Spine of Discrete Spacetime: Gravitational Wave Dispersion and LISA Falsifiability in Causal Dynamical Triangulations (GRU v2.4)

Version 2.4 of GRU (Geometría Radial Unitaria). Formal responses to three peer-review questions on propagation mechanism, crossing scale, and distinguishability. Central new result: GRU is the only quantum gravity theory predicting time-delay dominated gravitational wave dispersion in the LISA band. What's new in v2.4: §A.41 — Propagation mechanism: nGRU = 2·ds(spine)−2 = 0.0564 postulated and verified numerically at 0.31σ consistency with CDT data (not an ansatz). Formal derivation from Dittrich, Freidel & Speziale (2007) Regge Hessian framework in progress. §A.42 — Screening M1: λcorr=2.14±0.79 slices documented as phenomenological model. Suppression factor ~19 physically reasonable. Microscopic derivation deferred to CDT 4D collaboration (INFN Pisa). §7.4.8 — Time-delay dominated regime: GRU is the ONLY QG theory with n<1 + LISA window + quadrupolar j=2,m=0. Δt=277 ms at z=1 (detectable) vs Δφ=0.005 rad (negligible). 720σ separation from n=2; 349σ from n=1. Signature not covered by Gong 2023 (d=6) or SME d=5 (CPT-odd). Executive Summary table "GRU at a Glance" added — 9-row overview for new readers. §3.3 fitting window documented: proportional window [ILO=⌊0.2T⌋, IHI=min(2T,SIGMAMAX-5)], same as A.39. Convergence trend robust across both fixed and proportional protocols. 11 files in GRU_v2_4_scripts.zip including README.md with decision tree C1→C2 and full pipeline execution order for all versions (v2.2, v2.3, v2.4). v2.3 results confirmed: εA=4.1816%±0.0006% universal invariant, εA∝1/√N slope=−0.500, Dℓ=6.34 µK² (+0.67σ Planck). v2.2 results confirmed: λcorr=2.14±0.79 (21/32 CDT in LISA window), Afinal=1.46×10−16 ✅ This dataset and protocol are open for cross-validation on 4D CDT triangulation data. Collaboration inquiries welcome. Concept DOI (always latest): 10.5281/zenodo.20352929