Neutrinos as the fixed-point sector: why the lightest fermions mix the most, and why their mixing cannot be measured exactly

We argue, within a framework in which the matter spectrum descends from a single complexow (an unwinding spiral) whose modulus encodes scale and whose phase encodes structure,that the neutrino sector is distinguished by one fact from which the rest follows: it stops nearestthe end of the ow, where the running rate λ approaches zero. From this single placement weread o, without additional inputs, a chain of consequences that match observation: the tinyneutrino mass and the near-maximal neutrino mixing are the same fact (both say near the xedpoint); the neutrino is the one fermion forbidden a standard Dirac mass by the same structure(pointing to a Majorana nature); its mass scale coincides with the present position of the ow(the dark-energy scale); and its CP phase lives on an axis orthogonal to the mixing angles,predicting that CP violation is not xed by the mixing angles. The mixing angles themselvesare xed by the same structure that xes the charged-lepton masses (steps + angles + phase);they are determined. What is not accessible is their exact measured value: every measurementis made here, and reading here always carries the observer's variance x(1 − x) the samequantity that is quantum measurement uncertainty and cosmological tension elsewhere. Wetherefore predict an irreducible oset between the structural angle and the measured angle, oforder px(1 − x) aPl, that no experimental renement removes. The angles are not an openproblem; their exact measurability is the thing the theory forbids.