Two unresolved problems remain central in modern physics: cosmic acceleration at macroscopic scale and quantum state reduction at microscopic scale. These are usually treated in separate frameworks and at the level of three-dimensional bulk dynamics. A different possibility is considered here. Both are examined in terms of two-dimensional boundary geometry through a scale-invariant master relation. Information transfer is written as a boundary-crossing process governed by geometric scale, transition frequency, and a dimensionless transmission efficiency. The macroscopic limit is associated with horizon-scale saturation, whereas the microscopic limit is associated with radiative extraction through a finite decoupling surface. In the reduced boundary law, bulk parameters such as G, M, ħ, and k_B enter the intermediate description but cancel in the final form. At the microscopic level, comparison with quantum electrodynamics yields a definite ratio between the realized QED rate and the proposed boundary ceiling. If the same reduced law describes both horizon-scale kinematic structure and microscopic radiative scaling, then cosmic expansion and quantum state reduction may be treated as distinct regimes of a common boundary geometry.