- Change N=1->2 split policy from down to right to establish 2 full-height columns - Share single decision table across GUI and headless modes - Add _full_height_pane guard to prevent half-height column splits - Quadruple-wire default max_columns=2 and max_rows=2 across layout.py, lib.sh, and .mam.env.example - Update unit and integration tests to enforce deterministic 2x2 grid trajectory