Physical-Extension Underdetermination for a Pre-Spatial V₀ Ontology

A pre-spatial or non-spatiotemporal ontology does not, by itself, specify what would count as its physical realization. This problem is distinct from the task of deriving emergent spacetime from an already specified fundamental physical theory: before an empirical test can be attributed to an ontology such as V₀, one must determine whether the ontology carries any non-eliminable physical relevance, what independently defined physical quantity or structure is asserted to depend on an additional V₀-related physical extension, and how that extension differs from a declared ordinary-physics comparator. We develop a conditional physical-extension framework for a minimal V₀ ontology in which V₀ is not identified with the ordinary quantum-field-theoretic vacuum or an ordinary spatial region and is not assigned primitive spacetime structure. We distinguish ontological existence, physical relevance, accessibility, and observability; define target-indexed structural and dynamical physical-extension hypotheses; and give a minimal common-reduct model construction showing that a neutral ontology/interface core does not itself impose a structural-to-dynamical or dynamical-to-structural implication for the selected extension statuses. We further show that a nonempty ontology-to-physics interface specification does not entail physical relevance. Consequently, if a strengthened theory fixes an extension status that the neutral base leaves open, the strengthening is non-conservative with respect to the relevant physical-extension vocabulary and therefore introduces extension-relevant physical information. Downstream empirical discrimination is formulated through an observation map and nuisance-closed prediction families. The framework treats experiments as tests of explicitly augmented V₀-plus-physical-extension models, not of the bare ontology in isolation. No claim of physical detection, coupling, mechanism, or unique physical realization of V₀ is made.