The Infinite Echo: a State-Mirror Bug That Applies the Effect but Not the Dedup Key - Do Code That Matters

▤ Summary

This article explains a smart-home feedback loop caused by two MQTT-connected light switches mirroring each other incorrectly. The core bug appears when the receiver applies a relay change but does not update the deduplication state, so each side keeps treating the echoed message as new. The author traces the issue with live logs, rules out a boot-race theory, and then shows why a Tuya device behaves differently from a plain ESP device. The fix is to send a sync event that updates the local state variable before switching the relay, which stops the loop after one hop. The piece also highlights a broader pattern that can affect any event-driven system with echo suppression.

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