Multi-step agent safety stops checking each step alone: TAS caps tail risk with one shared budget, cutting average attack success to 45.15%
Risk in multi-step LLM agents propagates along the workflow, and step-by-step independent verification does not see that propagation. TAS models workflow safety states as a Markov decision process, measures rare but high-cost tail risk with a spectral risk measure, and constrains each step's decision with one budget shared across steps. On Agent Security Bench, TAS reaches average attack success rates of 45.15% under direct prompt injection and 29.73% under indirect prompt injection, below the eleven defense baselines it compares against.