Spiral-Domain Coordinate Transformation as a Lossless State Substrate for Digital Twins of Articulated Systems

v2 update (2026-06-01): Reproducibility ZIP added back to the latest version alongside the manuscript files, so that downloading from the concept DOI gives all materials in one place rather than requiring navigation to v1. This revised deposit contains the Paper 2 manuscript (PDF and DOCX) along with the supplementary reproducibility archive. The manuscript files were added in this revised version of the deposit; the supplementary ZIP file remains unchanged from the original deposit. Manuscript targets a biomedical-engineering venue (under preparation). Coverage. 8 pre-registered studies (Studies 21-27, Phase IV-V of the spiral-domain encoder validation campaign). Per-study reports, deterministic Python runners under PYTHONHASHSEED=0, raw CSV outputs, summary JSONs, and encoder source code. Contents. Manuscript (PDF and DOCX of the paper itself); supplementary reproducibility archive (46 files, 408 KB) including pre-registrations, per-study verdict reports, deterministic runners, raw data outputs, and source code. Reproducibility. The supplementary archive is reproducible end-to-end under PYTHONHASHSEED=0 on a standard Python 3.9+ installation with NumPy 2.0+. Reference machine: Apple Silicon arm64 (M-series), macOS 14. See archive README.md for per-study run commands. Methodological discipline. Every hypothesis was pre-registered with externally anchored decision rules frozen prior to runner execution. Zero post-hoc threshold adjustments were applied. Honest bounded negatives are interpreted substantively rather than discarded. Related companion archives. Paper 1 (10.5281/zenodo.20129137), Paper 3 (10.5281/zenodo.20139171), and the corresponding Papers 4, 5, 6, 7, 8 archives in this same Zenodo collection (Paper 8 at 10.5281/zenodo.20466035).