Relational Actualism (RA) proposes that the transition from quantum potentia toclassical actuality is grounded in a precise physical criterion: an irreversibleincrease in quantum relative entropy Δ S(ρ\|σ₀) > 0 with respectto the vacuum. In the perturbative regime this coincides with the on-shellcondition p^μ p_μ = m²c², at which a mediating boson crosses thekinematic threshold from virtual to real and an irreversible vertex is inscribedinto the growing causal DAG. This paper develops the implications for quantumcomputing and quantum thermodynamics. For quantum computing, the Kinematic Snap provides a principled physical flooron decoherence and yields the *Kinematic Coherence Bound*: the maximumfault-tolerant array size is N\ₘax = η · pₜh,where η is the single-qubit quality factor and pₜh is thefault-tolerance threshold. This is a structural constraint not anticipated bystandard quantum error correction theory: logical error rates grow with Nbecause each added qubit is an additional kinematic site at which actualizationcan occur. For quantum thermodynamics, RA grounds Landauer's principle in the causal DAGstructure, resolves Maxwell's demon without information-theoretic postulates,gives the fluctuation theorems a precise actualization-event interpretation, andestablishes that the thermodynamic arrow of time is structural rather than emergent. A key technical result: the quantum relative entropy is frame-independent by amachine-verified Lean 4 theorem (`frame\_independence` in`RA\_AQFT\_Proofs\_v10.lean`), proved using the continuous functionalcalculus unitary-conjugation lemma of the Lean-QuantumInfo library. Thefault-tolerance threshold, the speed of light c = lP/tP, and the biologicalCausal Firewall are all the same Erdős-Rényi percolation transitionat different scales of the causal graph.