In LLM-based Text-to-SQL systems, unanswerable and underspecified user queries may generate not only incorrect text but also executable programs that yield misleading results or violate safety constraints, thus posing a major barrier to safe deployment. Existing refusal strategies for such queries either rely on output-level instruction following, which is brittle due to model hallucinations, or on estimating output uncertainty, which adds complexity and overhead. To address this challenge, we first formalize safe refusal in Text-to-SQL systems as an answerability-gating problem, and then propose LatentRefusal, a latent-signal refusal mechanism that predicts query answerability from intermediate hidden activations of an LLM. We introduce the Tri-Residual Gated Encoder (TRGE), a lightweight probing architecture, to suppress schema noise and amplify sparse, localized question–schema mismatch cues that indicate unanswerability. Extensive empirical evaluations across diverse ambiguous and unanswerable settings, together with ablations and interpretability analyses, demonstrate the effectiveness of the proposed scheme and show that LatentRefusal provides an attachable, efficient safety layer for Text-to-SQL systems. Across four benchmarks, LatentRefusal achieves an average F1 of 88.5% and 88.8% on Llama-3.1-8B and Qwen-3-8B respectively, while adding ~2ms probe overhead.

Large Language Models (LLMs) frequently exhibit performance degradation in specialized domains due to distribution shifts. While unsupervised Test-Time Adaptation (TTA) offers a lightweight solution, existing methods suffer from critical flaws: input-centric adaptation lacks reasoning constraints, while output-centric optimization falls into a "Confidence Trap" of reinforced hallucinations. We instead study Few-Shot Anchored TTA, where a small labeled support set is available, and propose Anchor-Tethered Test-Time Adaptation (AT-TTA), a framework that synergizes linguistic alignment with reliable reasoning. AT-TTA employs Dual-View Uncertainty Calibration, minimizing input perplexity for domain alignment and sequence-level output energy for generation consistency. Furthermore, to mitigate catastrophic drift, we construct a "Semantic Anchor" by fine-tuning on the labeled support set and its filtered augmentations, which serves as a stable domain prior and constrains the adaptation trajectory via an Energy-Guided Adaptive Replay strategy. Extensive experiments on the AdaptEval benchmark demonstrate strong performance across diverse domains, effectively preventing model collapse while maintaining high inference efficiency.