We present a minimal ontological constitution for the DCQ–FBT programme. Rather than proposing a complete dynamical model, this paper identifies the structural conditions under which a physical theory may count as admissible within the present framework. The central claim is that physical reality is not fundamentally object-based or fieldbased, but is instead grounded in invariant geometric and algebraic structure. Within this view, phase space, observables, dynamical histories, and discrete physical sectors arise as constrained readouts of a deeper symplectic and topological substrate. We formulate four postulates that define this constitutional layer: (i) Structural Realism, specifying the ontological primacy of invariant structure; (ii) Symplectic Admissibility, defining the criterion of physical observability; (iii) Modal Determinism, characterizing the structural selection of realized histories; and (iv) Topological Locking, explaining the stability of discrete, integer-valued, and quantized sectors. These postulates do not by themselves constitute a finished physical theory. Their role is to delimit the admissible form of any realization in which emergent spacetime, admissible phase space, and topologically protected observables arise from an underlying geometric parent. The present version updates the established structural results of the FBT programme to reflect the substantial progress made through 2026, including the organisational cluster (FBT13A/B), the dimensional bridge (FBT15A), the central-output variational layer (FBT14A), the unified master equation and its gauge-side reduction (FBT12A/B), and the gravitational and scalar response frameworks (FBT10A/B).