TrajDebug能从长轨迹里精准揪出导致最终失败的那个错误，486条真实数据验证过，比现有方法都靠谱。
TrajDebug提出错误生命周期追踪框架，通过多粒度历史压缩和基于证据的错误识别，解决长轨迹中的错误发现难题。该框架追踪每个错误的解决状态和终端影响，实现关键归因。研究构建了TrajErrBench基准，包含来自Tau2Bench和SWE-Bench Pro的486个手动标注失败轨迹。实验表明TrajDebug在多个智能体基准上优于现有基线，其诊断结果可提升下游智能体成功率。
TRAJDEBUG: Tracing Error Lifecycle to Identify Critical Failures in Long-Horizon Agent Trajectories
LLM-based agentic systems have shown remarkable capabilities in complex domains, while suffering from cascading errors and difficulty in debugging. Critical error detection aims to locate the earliest error step in a failed trajectory that is responsible for the final failure. However, progress faces two main challenges. First, long trajectories make it difficult to identify individual errors, since the evidence for judging a step may be scattered across distant instructions, observations, and prior context. Second, failed trajectories often contain multiple local errors with different downstream effects, only some of which remain responsible for the final failure. In this work, we propose TrajDebug, an error-lifecycle tracing framework that addresses long-trajectory error discovery with multi-granularity history compression and evidence-based error identification, and supports critical attribution by tracing each error's resolution status and terminal impact. We further construct TrajErrBench, a benchmark of 486 manually annotated failed trajectories from Tau2Bench and SWE-Bench Pro, covering realistic tool-use and coding scenarios. Experiments across diverse agent benchmarks show that TrajDebug achieves the best overall performance over existing baselines, and application studies further demonstrate that its diagnoses provide actionable feedback for improving downstream agent success. We will release the codes and data to facilitate further research.