Quark Flavour in Causal Quantum Spacetime Theory: Graded Generation Charges from the Isotropic Vector Matrix

We examine the quark sector of Causal Quantum Spacetime Theory (CQST), whose substrate, in the face-centred cubic realisation adopted here, is the isotropic vector matrix. Relative to the ternary stacking axis the bond space has four exact properties, and five routes to quark flavour are closed by exact no-go results. The central quantitative finding is an asymmetry: the lattice bond geometry generates PMNS-like mixing generically and CKM-like mixing almost never, the two regions of parameter space differing in measure by about three orders of magnitude. The difficulty of the quark sector is therefore not the magnitude of mixing but its grading. The CKM requires ordered generation charges a = (3,2,0) under a single expansion parameter lambda = 0.225, and the same parameter reproduces the four independent quark mass ratios, so that mixing and mass hierarchy are one problem. A causal Gauss law built from the unique traceless rank-two tensor of a link takes the exact values +1 on the polar and −1 on the equatorial bonds, vanishes on the vacuum and gaps same-class continuations; polar–equatorial alternation is thereby selected dynamically, and neutrality with ternary closure forces a six-tick cycle. The graded charges follow if and only if the resonance re-enters the physical sector on a layer-changing move. A single colour channel cannot fix this phase; two recoupled channels can, by interference, but by at most a factor 2.23, and the recoupling propagator is derived from the diquark Casimirs and the sixty-degree recoupling angle. The quark sector thus reduces to the relative sign of two colour–bond vertices, two of whose three possible values falsify the construction. All numerical statements are reproduced by a supplementary script.