The Causal Spine of Discrete Spacetime: Gravitational Wave Dispersion and LISA Falsifiability in Causal Dynamical Triangulations (GRU v2.3)

Version 2. 3 of GRU (Geometría Radial Unitaria). New central results: εA = 4. 1816% ± 0. 0006% — universal invariant, verified across 5 independent seeds and scaling law εA ∝ 1/√N confirmed with slope = −0. 500 exact. CMB quadrupole bug corrected. What's new in v2. 3: εA = 4. 1816% ± 0. 0006% — Universal Invariant: Measured by gravitational wave injection experiment on GRU causal mesh (N=20 shells, 2560 nodes). CV = 0. 015% across 5 seeds. Zero frequency dependence → purely geometric effect. Scaling law εA ∝ 1/√N verified: slope log-log = −0. 500 exact (N=10→5. 91%, N=20→4. 18%, N=50→2. 65%, N=100→1. 87%, N=200→1. 32%). Confirms analytic Mewes formula. CMB bug corrected: v2. 2 used spurious denominator 1+ (κ/2. 5) ² with no physical derivation, giving Dℓ=3. 78 µK² (34% tension). v2. 3 canonical formula R2 (κ) = (1−e−√6·κ/2) ² gives Dℓ=6. 34 µK² (+0. 67σ from Planck 5. 77±0. 85 µK²) ✅ Fisher updated: σn=0. 0027 (1. 13× improvement), N=1 SMBHB event for 5σ unchanged. 12 new files in GRUᵥ2₃ₛcripts. zip: 3 scripts (MESHBUILDER, WAVEINJECTOR, EPSILONA) + 9 results. 3 new references: Ambjørn & Loll 2026 (arXiv: 2604. 05641), Gong et al. 2023 (PRD 107, 124015), Wang et al. 2025 (PRD 111, 084064). v2. 2 results confirmed: λcorr=2. 14±0. 79 (21/32 CDT in LISA window), Afinal=1. 46×10−16 ✅, nGRU=0. 0564, factiva=1. 0, ηint=0. 169±0. 038. Concept DOI (always latest): 10. 5281/zenodo. 20352929