SIGMA R15 / P14: bounded Maxwell audit and AI-provenance receipt proposal

Additive English technical note connecting two existing SIGMA branches without merging their identities. R15: finite-fixture arithmetic independently recomputed from the local R8 receipt for the sufficient penalty margin, the κh mesh sequence and a spectral cluster whose error increases. The R8 solver was not rerun; the historical β = 4 failure remains, and neither continuum nor physical validation is claimed. P14: proposed fields for an auditable AI on/off execution-path receipt; this schema is not yet implemented or tested. External research is cited without incorporating third-party code, figures or substantial text. The attached PDF and editable text contain no software. CC BY 4.0 applies only to the original explanatory documentation, not to cited works or earlier SIGMA source archives. Riccardo Giudici is an independent systems orchestrator; computational and AI assistance is disclosed, with no institutional endorsement implied. Related published P14 version: https://doi.org/10.5281/zenodo.23023504. This bounded technical note is not a claim of scientific certification.