A Strong-Field Observability Rubric for Modified Gravity: From Formal Wave Solutions to Binary-Merger Predictions Case Study: Spin-1 Hamiltonian Composite Gravity

This manuscript proposes a strong-field observability rubric for modified and alternative theories of gravity. The rubric is designed to distinguish formal mathematical structures - such as wave equations, static metrics, or linear perturbations - from observationally closed binary-merger predictions. It complements weak-field frameworks such as the parametrized post-Newtonian formalism by specifying the additional source-native closure chain needed for gravitational-wave claims: matter coupling, detector response, native radiation flux, low-order radiation cancellation or bounds, inspiral phasing, ringdown spectra, causal propagation, and quantum closure when quantum stability is claimed. The paper calibrates the rubric against the classical general-relativistic binary-merger program and explicitly scopes the rubric as an inductive, source-native closure checklist rather than a theorem or replacement for weaker exploratory tools. Version 1. 2 strengthens the peer-review enforcement layer in response to red-team critique: it frames the Milestone-0 halt as a protective audit firewall, removes the former conditional tetrad-to-strain calculation as a usable appendix result, replaces it with a rejected-shortcut appendix, and adds an operational referee checklist translating the milestone rubric into concrete review actions. The triptych consists of: (1) classical general relativity as the benchmark where the classical chain closes through the ringdown milestone, (2) spin-1 Hamiltonian composite gravity as the primary case study that halts at Milestone 0 because the source theory does not derive matter coupling or test-mass response, and (3) scalar-Gauss-Bonnet / Einstein-dilaton-Gauss-Bonnet ringdown calculations as later-stage comparison cases that reach Milestone 5 but require coupled scalar-tensor perturbation systems, slow-rotation or small-coupling expansions, eikonal limits, and numerical validation rather than the clean GR master-potential closure for generic configurations. The audit finds that strict application of the rubric still halts at the matter-coupling milestone for the Hamiltonian composite-gravity case study: the source theory does not derive the matter action or test-mass response needed to convert field variables into detector motion. Downstream milestones remain open, including native compact-binary flux, low-order vector-radiation cancellation or bounds, inspiral phasing, ringdown quasi-normal modes, tetrad causality, and Ward-identity/quantum closure. The result is not a falsification claim. It is a closure classification: the case-study theory has not yet earned binary-merger observability under the proposed rubric. The revised Appendix A explicitly treats the tetrad-to-strain move as a rejected shortcut unless and until Milestone 0 is closed by a source-native matter-coupling derivation. Files Included: - mainᵥ120. pdf - Final compiled manuscript. - mainᵥ120. tex - REVTeX 4. 2 source file. - strongfieldᵣubricᵥ120ᵣelease. zip - Reproducibility bundle containing the compiled PDF, LaTeX source, compile report, SHA256 checksums, Zenodo metadata, X-post draft, and rendered PDF contact sheet.