Nucleon Packing into the Lattice: A p-n Bag-to-Shell Correspondence Preserving the Magic-Number Skeleton

We extend the neutral 24-cell (D4/R4) fill scaffold with a label-only p/n species layer that preserves the upstream rigidity skeleton (Bones) as the carrier of magic-number structure while allowing net charge to be represented separately. Each occupied 24-cell in the canonical neutral fill CA receives a species label ℓ : CA → {p, n} and four placeholder property labels (rp, rn, rx, c1). On composition, (rp, rn, rx) migrate holonomically inward (rigidity-to-core) and c1 migrates holonomically outward (charge-to-surface, repulsion-minimizing boundary condition). We define a deterministic relaxation operator T (executable given upstream tie-breaks) that maps arbitrary initial labelings to a canonical “bag-to-shell” fixed point. We then specify minimal fusion (attachment) and fission (cut/scission) accounting requirements for these labels, and define spectral-gap observables (f1, f2) as low/high bounds around a rigidity lock, avoiding mass-based proxies. We publish obligations to construct (rp, rn, rx, c1) geometrically within a single 24-cell and to define the spectral operator on CA, and we publish falsifiers that can kill the brick if the interface cannot reproduce empirical shell-gap signatures or scattering radii calibration targets.