Coding Agents Don't Know When to Act
This study addresses a critical yet overlooked issue in AI-driven code generation: coding agents frequently introduce redundant changes when confronted with already-fixed bug reports, mistaking them as requiring modification and thereby accruing technical debt. The work presents the first systematic characterization and quantification of this “action bias,” introducing FixedBench—a benchmark designed to evaluate agents’ decision-making in scenarios where no code change is necessary. Through human-validated tasks, a multi-agent evaluation framework, and instruction fine-tuning, the authors find that state-of-the-art large language models still produce inappropriate code modifications in 35%–65% of such cases. While failure-reproduction guidance partially mitigates this bias, it simultaneously triggers new failure modes. The paper proposes a novel paradigm that explicitly models “inaction” as a valid and successful outcome, offering a crucial direction for aligning agent behavior with developer intent.