UC-021: Idempotency Failure Replay

Layer: C — Verifiable Receipts Threat: Session Replay

Scenario

An attacker attempts to replay a valid receipt or re-execute an already completed tool call by submitting a duplicate execution request.

Expected Behavior

• Duplicate execution request → rejected by idempotency cache
• Lamport clock monotonicity detects out-of-order attempts
• Causal PrevHash chain detects replay from different context

Pass Criteria

• Duplicate rejected (not re-executed)
• Original receipt remains valid
• No duplicate side-effect produced