Following the Skill, Failing the Patient:Procedural Inertia in Clinical Agents

Clinical agents are increasingly built to carry out procedures by following reusable skills, and curated skills raise average task success. A skill, however, fits the patient as they were when it was selected, and new evidence can make it wrong while the agent is still executing it. We call the tendency to keep following an invalidated skill procedural inertia. To measure it, we introduce SkillInertiaBench, a clinician-reviewed benchmark of 576 cases in six procedure families, in which each routine case is paired with three variants that differ only in the invalidating evidence and its timing: before execution, as a pre-existing fact revealed during execution, or as a change in the patient's state. Across two model families, standard skills raise routine completion from 67.7% to 80.6% but lower later-contradiction completion from 62.2% to 44.8% and raise harmful persistence from 31.2% to 49.8%; half of these harmful continuations follow the agent's own statement of the invalidating evidence. We then propose PatientGate, a patient-first execution policy in which an independent reviewer rechecks the active skill against the current patient state before each action and a gate enforces its verdict. PatientGate raises later-contradiction completion to 69.8% and lowers harmful persistence to 25.3% while keeping routine completion at 79.9%. These gains hold across both model families, two public benchmarks, and three clinical skill strategies. Our results make skill validity, not only skill quality, a first-class requirement for clinical agents, and show that it can be enforced at inference time without retraining.