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Webhooks are not a trivial problem at scale. When you're processing thousands of events per second, your strategy matters. Webhooks are usually delivered at-least-once. Assume duplicates and out-of-order events are the norm, not the exception.

Idempotency isn't just a nice-to-have - it's critical. Your webhook handler needs to handle the same event multiple times without side effects. Synchronous webhook processing? Recipe for disaster. You'll hit timeouts, dropped connections, and potentially trigger retry storms.