One duplex WebSocket session. Every client frame carries an integer protocol `code` and a client generated `trace` id; every server frame echoes the `trace` on acknowledgements. A heartbeat (code 10010) must be sent at least once per minute or the server treats the connection as inactive and closes it.
The AsyncAPI specification describes event-driven APIs the way OpenAPI describes request/response APIs. A channel is the named pipe — a webhook URL, a Kafka topic, a WebSocket route, an MQTT subject — that producers and consumers publish or subscribe to. Each channel carries one or more messages with structured payloads, and an operation declares whether a given party sends or receives on that channel.
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