Landauer Saturation in Hawking Evaporation and an Information and Energy Accounting Framework

Building on Cortes and Liddle's result that Hawking evaporation saturates the Landauer bound, we develop an information and energy accounting framework for black hole thermodynamics. The identity T_H S_BH = (1/2) Mc^2 for Schwarzschild black holes is the Smarr relation; the factor of 1/2 is forced by the holographic scaling S_BH proportional to M^2 (area law). We use this identity as an interpretive bookkeeping device to organize an information/field-cost accounting language, and show through counterfactual analysis that the 1/2 would change to 1/k if entropy scaled as M^k instead. The framework positions black holes as the thermodynamic complement to quantum measurement in the record-formation regime: measurement creates classical records by paying Landauer costs (under conditions C1 to C6), while black holes render those records operationally inaccessible to exterior observers and return the costs as Hawking radiation. We verify the accounting dynamically across the full evaporation trajectory and across the Kerr and Reissner-Nordstrom parameter spaces, including extremal limits where T_H approaches zero.