Vacuum Energy as a Source-Descent Problem: Projective Quantum Generators, Central Reactivation, and Residual Cosmological Response

This paper develops a structural reformulation of the cosmological constant problem by distinguishing between quantum-generator representatives and the physical quantum equivalence classes they define. In ordinary quantum theory, adding the same constant energy offset to all states does not change projective state evolution, density-operator dynamics, observable evolution, or measurable state–effect probabilities. This suggests that the absolute common energy baseline belongs to the representation of the quantum theory rather than to its physically distinguishable content. The paper asks whether the gravitational source should respect that same equivalence. This leads to a precise notion of source descent and to a central-reactivation obstruction that measures when gravity becomes sensitive to a quantum direction that is otherwise operationally redundant. The analysis also separates common-mode vacuum shifts from physically meaningful differences between distinct vacuum branches, develops a support-normalized response construction, and derives a minimal residual structure for source information that cannot be discarded without physical loss. A conditional framework is then developed in which any nonzero cosmological response arises not from the absolute quantum vacuum baseline itself, but from residual quantum–event structure that survives after the common baseline freedom has been removed. The paper does not claim a completed solution of the cosmological constant problem. Instead, it presents a mathematically explicit reformulation, several exact structural results, a set of no-go statements, and a focused theorem programme for determining whether gravitational sourcing can consistently depend only on physically distinguishable quantum structure.