Quarantine is a risk containment mechanism. An agent that is modifying security-critical files, consuming tokens at an anomalous rate, opening an unusual number of pull requests in a short window, or repeatedly failing the same task is exhibiting patterns that warrant investigation before further execution.
The quarantine mechanism should be automatic — triggered by threshold breaches without waiting for a human to notice — and the threshold configuration should be explicit and auditable. 'The agent was quarantined because its risk score exceeded 0.8 due to modifications to auth/middleware.go and payments/stripe.go' is actionable; 'the agent was stopped' is not.
Quarantine is distinct from simply stopping an agent. A stopped agent can be restarted without review. A quarantined agent requires an explicit human decision to re-enable, creating an intervention point where the human reviews what triggered quarantine and whether the underlying cause has been addressed.