Deriving Generalised Quantum, Gauge, and Gravitational Structures from Reference Frame Self-Consistency on Nonlinear State Manifolds

The companion paper (Tang, 2026) showed that the Self-Consistent Reference Frame Principle (RCC), applied to local Hilbert-space fibres, yields the Born rule, the Yang--Mills action, and the Einstein--Hilbert action as consequences of reference-frame self-consistency and causality. (In that derivation, "quantum foundations" refers to the Born rule and the emergence of Hilbert-space structure; unitary dynamics, the tensor-product rule for composite systems, and the measurement postulate lie outside its scope.) The present paper removes the linearity assumption. It reformulates RCC on nonlinear state manifolds---smooth manifolds without a preferred linear or metric structure, on which symmetry groups act by diffeomorphisms. The core object is the nonlinear comparator, a G-equivariant diffeomorphism between fibres that translates reference frames. Each result of the linear paper---the Born-rule probability formula, the gauge connection, the gravitational metric, and the phase unity identity---is reconstructed in this more general setting and reduces to its linear counterpart precisely when the state manifold carries a Kähler structure, the geometric condition under which P=|⟨φ|ψ⟩|² is recovered. (Unitary dynamics, the tensor-product rule, the observable algebra, and the measurement postulate remain external inputs.) The nonlinear framework reveals structures inaccessible in the linear case: the Born rule generalises to a family of G-invariant transition functions; gauge theory arises as a special case of fibre-bundle geometry with a nonlinear G-action; nonlinear comparator corrections---torsion and anholonomy effects from the curvature of the fibre---generate additional SMEFT operators, most notably O₃B with C₃B≠0; and the gravitational sector receives subleading corrections from fibre-valued geometric invariants. The nonlinear framework yields a strictly larger set of falsifiable predictions: the linear results are recovered in the Kähler limit, while the deviations constitute a new experimental window into the geometry of state space.