A Conditional Structural Organization of the Light-Baryon Spectrum: Eighteen Channels and Nucleon Mass Ratios

Quantum chromodynamics (QCD) is the established dynamical account of light baryons. This paper asks whether their ground-state organization and dimensionless mass placement can also be represented by a finite reconstruction calculus. Given a three-grade rooted bilateral incidence complex, twenty-seven ordered routes reduce under the invariant side exchange to exactly eighteen classes. Complex linearization gives the standard representation identity Sym2(W)⊗W≅Sym3(W)⊕S(2,1)(W), with dimensions ten and eight. Identifying these sectors with the physical decuplet and octet is an explicit light-flavor correspondence postulate; the result is therefore a structural reorganization of known flavor combinatorics, not an independent derivation of the observed multiplets. A scale inherited from the published charged-lepton construction and finite operators then organize the masses. Data-informed closed-neutral and charged-boundary closures reproduce the neutron-electron and proton-electron ratios within 0.92 and 0.35 quoted experimental uncertainties. The leading seven-centroid comparison uses two common normalization integers and five effective discrete operator weights for seven values, so it is not an overdetermined prediction. Higher centroid and charge fibers were recognized with knowledge of the spectrum; their level-six agreements are consequently experimental-normalized reproducibility diagnostics, not statistical significances. A quadratic-local obstruction theorem excludes a simpler sector-blind charge selector, and the frozen carrier-lift complex gives a prospective Delta charge pattern. Published law-constant co-selection results motivate the common structural setting but do not prove the baryon-specific fibers. No continuously adjusted baryon-sector scale or measured fine-structure constant is inserted. The finite mathematics is exact within the declared complexes, while physical selection remains conditional; QCD and QED remain indispensable after read-out.