MIsCORE–RIUD: Paper VIII Horizon Formation, Relaxation, and the GR-Side Mechanism

Paper VIII is the integrative physical-mechanism paper of the MIsCORE–RIUD research program. It asks whether the merger-local higher-order organization first identified in gravitational-wave residual data survives successive changes of representation from residuals to unsubtracted detector strain, source-native numerical relativity, dynamical-horizon geometry, outgoing radiation, and a forward detector projection. The analysis preserves an important negative result: a blind event-specific RAW/source landmark search did not produce stable independent population-wide recovery. Instead, conditioning only on the previously frozen RIUD structural GAP reveals a multiplicity-controlled RAW transition neighborhood in a 95-event complete join. Source-native SXS simulations then place the corresponding detector-like response on the pre-common-horizon side, near a frozen location of approximately AhC−25M. The location identified in an exploratory SXS10 cohort reproduces without retuning in five additional simulations, while the combined SXS15 population shows coherent acceleration of waveform growth, frequency growth, binary separation decrease, and plunge/infall progression. After common-horizon formation, an Einstein Toolkit dynamical-horizon calculation closes the known Ashtekar–Krishnan balance at approximately the percent level under the frozen numerical contract, with shear and the 2ζ2\\zeta contribution accounting for the measured horizon growth and same-run Ψ4\\Psi_4 providing the outgoing-radiation branch. A final posterior-conditioned GW150914 analogue, evaluated through the recovered historical R0 operator, gives synthetic-versus-observed landmark offsets of 16, 4, and 1 ms at 5, 10, and 20 ms widths, respectively. This final branch is classified as partial forward positional support, not exact end-to-end historical parity. The central result is therefore not an algebraic identity between residual, RAW, source, horizon, and detector-forward variables. Rather, Paper VIII supports a higher-order cross-representation physical organization whose scientific ordering survives while the lower-order representation changes: Residual higher-order object → RAW transition/persistence → pre-AhC plunge/infall → apparent common horizon → shear + 2ζ2\\zeta horizon growth → Ψ4\\Psi_4/radiation → partial forward detector support. Paper VIII is intended to be read as the integrative culmination of the sequential MIsCORE–RIUD program and assumes the observational objects, population dynamics, internal-time framework, structural GAP, and representation boundaries established in Papers I–VII. Related integrated volume https://zenodo.org/records/22254049 Standalone Papers MIsCORE–RIUD: Paper IDefining and Falsifying Recurrent Merger-Local Morphology in Gravitational-Wave Post-Model Data https://zenodo.org/records/22319453 MIsCORE–RIUD: Paper IIConnected Multiscale Paths in Gravitational-Wave Post-Model Data https://zenodo.org/records/22278310 MIsCORE–RIUD: Paper IIIPartially Shared Dynamics in Recurrent Gravitational-Wave Undiscovered Paths https://zenodo.org/records/22282910 MIsCORE–RIUD: Paper IVPopulation Dynamics and a Frozen Physical Clock https://zenodo.org/records/22313433 MIsCORE–RIUD: Paper VCross-Representation Regimes and Physical Sectors in Black-Hole Merger Dynamics https://zenodo.org/records/22332074 MIsCORE–RIUD: Paper VIFrequency, Timing, Geometry, and the Mechanism Boundary https://zenodo.org/records/22409081 MIsCORE–RIUD: Paper VIIDetector Representation, Minimum Common Support, and the Observation Boundary https://zenodo.org/records/22651472 MIsCORE–RIUD: Paper VIIIHorizon Formation, Relaxation, and the GR-Side Mechanism https://zenodo.org/records/22761577