A Reproducible Pre-SPH Validation Architecture for Impact-Triggered Lunar Angular-Momentum Reversal

Conservation-law screening can identify conditions under which a retrograde orbital reservoir would have sufficient angular momentum to overcome a terrestrial spin budget. It cannot establish that a collision produces such a reservoir. This paper specifies a reproducible validation architecture for that unresolved step in the Impact-Triggered Lunar Angular-Momentum Reversal (ITLAMR) programme. The architecture connects controlled contact-state construction, equation-of-state and particle preparation, hydrodynamic calculations, fragment reconstruction, early gravitational evolution, and a later tidal handoff. The central C45 reference uses a cold, nonrotating dunite target and impactor with mass ratio 1.25, impact speed 1.4 times mutual escape speed, and contact angle 45 degrees. Strength-bearing and strengthless configurations are retained as separate controls. Publication endpoints distinguish aggregate orbital angular momentum from fragment spin and diffuse debris. Physical and strong orbital screens, numerical rejection rules, a twelve-case core, and a conditional forty-case expansion are specified before production outcomes. A constants bridge preserves the distinct Paper I and Gate/production conventions: the same finite-mass circular-budget equation gives 243191.591460 and 243236.402398 km, respectively. The companion package includes prepared inputs, an EOS-geometry three-body reference, a corrected full-vector particle partition, and twenty-two passing synthetic CPU checks. These establish input identity and tested computational behaviour. No production GPU relaxation, physical hydrodynamic collision, early N-body survival result, or demonstrated Earth-spin reversal is reported.