From Multiphysics Conflict to Computational Substrates: Differentiable Structural Synthesis and Stoppable Active Foundations under SBE/DSR

This preprint establishes Computational Substrates and the Physics-Constrained Neural-Operator and Adjoint Electronic Design Automation (PCNO-EDA) framework. Boards and packages are treated as synthesizable physical entities that must simultaneously organize SI, PI, thermal, and thermo-mechanical reliability relations. PCNO-EDA is explicitly positioned as an inverse-synthesis accelerator and screening layer upstream of commercial EDA, not a replacement for DRC/LVS/sign-off. A three-stage stoppable maturity protocol separates passive multiphysics synthesis (Stage 1, stoppable commercial endpoint) from optional tunable and active reconfiguration stages that require hardware redundancy. This record is a conceptual and theoretical preprint. No original experimental dataset is reported. It is Paper 6 of the SBE/DSR Structural Substrates track and closes the series into a computational-substrate research programme.