Exact Vacuum Zero Modes in Compact Top-Form Sectors: Source Assignment and Radiative Stability

This paper formulates a source-assignment criterion for exact spacetime-constant vacuum shifts in gravitational effective field theory with compact top-form sectors. The purpose is not to predict the observed cosmological constant, but to state when an exact zero-derivative vacuum contribution is assigned to global flux data rather than to the primitive local stress tensor. A minimal compact three-/four-form model is given in which the constrained mode is fixed by global flux labels, the corresponding local equation has Einstein form with a flux-fixed label [Formula: see text], and the operator inventory identifies when exact constant vacuum shifts renormalize the global branch relation rather than an independent local cosmological-constant counterterm. Local excitations, curvature-dependent terms, rolling fields, finite-temperature energy densities and ordinary matter remain in the local sector and gravitate normally. A worked scalar-sector example compares ordinary local-source assignment with the flux-fixed source-assigned treatment, showing explicitly how a constant vacuum shift is separated from local stress while local matter still gravitates. A source-status comparison distinguishes the protected flux-fixed geometric label from a static local volume coupling and from a rolling local scalar source. The criterion is compared with four-form neutralization, unimodular gravity and vacuum-energy sequestering. The result is conditional and falsifiable: hard local potentials for the constrained mode, gauge-breaking three-form masses, non-topological local couplings [Formula: see text], or independent local [Formula: see text] counterterms take a realization outside the admissible class.