Does Catalyst guarantee exactly-once execution for external API calls from AI agents?

No. Durable execution does not automatically make external side effects exactly-once. Catalyst provides durable workflow state and replay, but idempotency and reconciliation for external API calls remain the application's responsibility. This is the same for Temporal and Restate. Catalyst's verifiable execution can help audit what happened, but you must design your agent logic to handle duplicates or failures at the integration layer.