arXiv:2610.30911v1 Announce Type: new Abstract: Semantic communication systems based on deep joint source-channel coding can provide task-oriented wireless transmission, but adversarial robustness may require substantial radio and receiver-side defensive-computation energy. This paper develops an energy-efficient, risk-constrained semantic communication framework under source-domain, over-the-air (OTA), and potentially composite adversarial conditions. Long-term total energy, including communication and diffusion-purification energy, is minimized subject to average semantic-loss, trajectory-level tail-risk, and end-to-end latency constraints. A recurrent primal-dual proximal policy optimization controller jointly adapts transmit power, semantic/channel bandwidth ratio, and purification complexity using causal channel observations, semantic confidence, imperfect attack-belief estimates, and recurrent history. A conditional value-at-risk (CVaR) constraint explicitly limits severe semantic failures. On CIFAR-100, at the unseen source-domain level $\epsilon=12/255$, the proposed controller achieves approximately $61\%$ robust Top-1 accuracy with $\mathrm{CVaR}_{0.9}\approx0.36$ while using about $9\%$ less total energy than diffusion-only defense. At the unseen OTA level $\Gamma_A=-5$ dB, it achieves approximately $52\%$ robust Top-1 accuracy, reduces semantic tail risk by $40\%$, and consumes about $8\%$ less total energy than diffusion-only defense. These results demonstrate energy-efficient semantic defense under partially observable adversarial conditions.