Entropy Production Corridor: Additivity Pressure, Coarse-Graining Monotones, and Irreversibility Slots

Irreversibility is a forced bookkeeping budget, not an imported entropy axiom. This paper derives an entropy-production corridor from three corridor-native pressures: additivity under independent subsystem composition, monotonicity under declared coarse-graining (data processing), and segmentation-invariant cumulative accounting. It proves logarithmic forcing on canonical multiplicative spectral subfamilies for admissible spectral divergences, defines per-step production as the forced nonnegative decrement under stationary CPTP updates, and establishes a telescoping irreversibility budget. Full uniqueness of the divergence representative and extensions beyond canonical spectral subfamilies are deferred.