Runaway tool-call loop within a single session - ATR-2026-00553 (52a91597-db2e-5ebc-8e66-b5c59a0aee37)
Detects a runaway tool-call loop where an agent emits more than 100 tool call spans within a one-minute window for a single session. This is a behavioral-method rule per spec/atr-method-v1.1.md §7, demonstrating the aggregation grammar (count over time window with per-session grouping and a min-events floor).
Threat model: prompt-injection attacks, agent goal-drift, or compound retry-loop bugs can cause an agent to enter a tight tool-call loop — retrying the same tool, polling a service, or exhausting a budget by calling many tools in rapid succession. The behavior is not visible in any single tool call (each call may be syntactically benign); the signature is in the aggregate frequency. The runaway pattern is the most common cause of denial-of-wallet incidents in production agents and the leading runtime symptom of agent goal drift in long-running workflows.
Suppression: min_events: 10 prevents false positives during cold- start where one or two early calls would otherwise trip the rule; cooldown: PT5M prevents alert spam after the first violation.
This rule is the canonical behavioral-method reference example shipped with v1.1 of the method-extensions spec.