BIT-U_B-01: A Conditional Explicit Boundary Update Operator and Boundary Stabilization Theorem — ET-PSC v0.1

This independent technical report presents ET-PSC, an event-triggered projected spectral clamp proposed as an explicit conditional form of the BIT boundary update operator UBU_BUB. Under stated convexity, fixed-point, Lipschitz and spectral conditions, a common Lyapunov argument establishes forward invariance of a prescribed corridor and exponential convergence in the finite-disturbance case. Two synthetic engines, ablation tests and persistent-disturbance stress tests are supplied. The result is not claimed as a universal solution to turbulence, a replacement for all MPC methods, or a field-validated controller.