Ever watched an email agent reply to the same message twice? The recipient gets two near-identical responses seconds apart, screenshots them, and your carefully engineered assistant suddenly looks like a script with a stutter. Worse: under real load, this isn't a freak event. It's the default outcome if you haven't designed against it.
The double-reply problem has three distinct causes, and each one needs its own fix. Let's walk through them.
Why duplicates happen at all
First cause: webhook redelivery. Nylas — like most webhook providers — guarantees at-least-once delivery. If your endpoint doesn't return a 200 fast enough, or a transient network blip eats the response, the same message.created notification shows up again. Process both, send two replies.
Second: concurrent workers. Your handler probably runs on multiple instances — Lambda invocations, ECS tasks, worker processes. Two of them can pick up the same notification at nearly the same instant and both start generating a reply.
