This paper studies three computational kernels of a digital-twin prototype for USV formations—a cyclic Jacobi routine for algebraic connectivity, a connectivity-driven formation-gain scheduler, and a hysteretic topology selector—verified through kernel-level spectral checks, frozen-topology linear consensus, and graph-level switching and fault analysis. First, the Jacobi routine’s equal-diagonal rotation matches symmetric eigensolutions on star, complete, and implementation-specific graphs of order 3–13 to . Second, for a frozen connected graph of m vessels, the scheduled gain yields , hence on . Third, with M constant-utility candidates and bounded observation noise, makes every accepted switch a strict ascent, permitting at most switches. Fourth, an isolation fault, via distinct full-diagnostic and online graphs, leaves a seven-vessel complete graph with , while a re-elected star on six online vessels recovers and versus messages per agent. Finally, a scalar ADRC stress test and its multi-agent extension show estimation-based rejection (∼) and gain re-scheduling (∼) act independently for a combined ∼ reduction in steady-state disagreement, with a switched-loop corollary bounding disagreement under finitely many switches at the frozen-topology rate. New experiments close the loop end-to-end: an integrated hysteresis–scheduling–ADRC loop holds the observer factor near across a star → mesh → star reconfiguration, hub-fault recovery gives a lower peak and faster settling than PD, and the rejection advantage holds at matched feedback authority, with the accuracy–effort trade-off against PD and LQR baselines quantified explicitly; the switched-loop corollary is stated for the full state (disagreement, relative velocities, observer errors) at rate consistent with the observer’s response speed.