Hu's Cosmic Spacetime Origin Theory (HCSOT): A Unified Modified Gravity Framework for Dark Matter, Dark Energy, and the Hubble Tension — V8.7 with Pre-Registered Euclid DR1 Weak-Lensing Prediction of +5.5% to +8.0% Enhancement at k=0.1 h/Mpc (First Archived: 10 April 2026; Finalised: 30 May 2026)

Hu's Cosmic Spacetime Origin Theory (HCSOT) is a minimal scalar-tensor modified gravity framework in which the energy density of a single universal scalar field governs gravitational dynamics. Dark matter and dark energy phenomenology are unified through density-dependent effective gravity. The theory fundamentally rejects the existence of dark matter and dark energy as independent physical particles. Pre-registered prediction for Euclid DR1 (October 2026): +5. 5% to +8. 0% enhancement in the weak-lensing matter power spectrum at k = 0. 1 h/Mpc relative to ΛCDM. Prediction timeline (fully timestamped on Zenodo): · 10 April 2026: Initial prediction publicly archived (8% ± 3%, range 5. 0%–11. 0%) · 30 May 2026: Final prediction locked and pre-registered (+5. 5% to +8. 0%, fiducial +6. 4%) · October 2026: Euclid DR1 data release — the decisive test Key features of V8. 7: · Complete linear perturbation equations with explicit anisotropic stress σ_φ · Nonlinear saturation model honestly disclosed as empirical parametrisation; rigorous nonlinear solution remains an open problem · Observational evidence hierarchically classified: core prediction / consistency checks / auxiliary cross-checks · Five explicit falsification criteria, including direct detection of dark matter particles as falsification · Three fundamental physical bounds (no singularities, no heat death, no unbounded gravitational binding) · α = 0. 087 independently constrained by local H₀ (SH0ES + H0DN) and Big Bang nucleosynthesis (BBN: α ≥ 0. 069) · Independent CAMB validation: CMB acoustic peaks preserved to <0. 01%; P (k) enhancement confirmed · Solar System constraints satisfied via natural nonlinear saturation (Gₑff deviation < 10⁻¹⁵) · 14 companion papers; 20 analysis scripts archived in separate code repository (DOI: 10. 5281/zenodo. 20104919) Version history: The original theoretical framework was first publicly archived as Version 1 on 10 April 2026. V8. 7 (01 June 2026) corrects the logical structure of the falsification criteria, restores the core position on dark matter particles, and adds independent CAMB validation. All theoretical predictions, parameter values, and core equations remain unchanged from the initial 10 April 2026 version through to the final pre-registered version of 30 May 2026 and this V8. 7. Licence: CC BY 4. 0