This paper develops the Operational Agency Horizon as a general framework for task-relative operational boundaries in the Volumetric Time Model (VTM). It unifies three previously separated structures: the steering horizon, where action-to-outcome coupling falls below detectability; the forecasting-without-power regime, where predictive coupling remains measurable after leverage has collapsed; and the readout horizon, where record-mediated access fails despite the continued existence of the target within the spacetime volume. The paper introduces a common formalism for horizon crossing, proposes an operational triage of couplings, and clarifies the distinction between existence, accessibility, leverage, and viability. It also situates the Agency Horizon, Leverage Gap, Operational Decoupling Window, Functional Horizon, and the No Access Without Readout principle within a single hierarchy. This is a conceptual and unifying paper rather than an experimental suite report. It is intended as the theory companion to the separate Experiment 10 paper, which provides empirical support for the separation of steering, readable structure, and functional survival into distinct measurable boundaries.
Ralph Clayton (Tue,) studied this question.