What this demonstrates
The fourth return combines the retained belt geometry and its mode signs with the spinor projection procedure. Frame normalization preserves both input components. The matrix bridge to the electron construction is checked independently.
This establishes one comparison square. It does not establish all relationships of a meta-tetrahedron: the original proton and belt returns each select one complex mode, while these two returns retain two components. No particle name, charge or mass is assigned to the fourth.
The 312-transfer core has L:24, G:144, N:144. The separate 12×8 bridge is not included in that core count. Guide lines are not coefficient arrows.