\section*{Declaration of generative AI and AI-assisted technologies in the manuscript preparation process}

Claude Code (Anthropic) assisted the original preparation. OpenAI Codex assisted this revision with proof auditing, the explicit helicity-span argument, the null-current lemma, scope corrections and editing. The numerical programs are supplementary checks; they do not certify the general field-theoretic statements. Responsibility for reviewing and approving the final mathematical content rests with the author.