Ingress behaviours wrapped around every subscription handler — the messaging arm of the transport-neutral behaviour chain shared with the websocket, queue, and scheduler plugins (IIngressBehavior in @setu-ts/common).

Each behaviour observes an IngressContext carrying kind: 'messaging', the topic as name, the delivered message as payload, and the transport headers from MessageMetadata (absent when the transport carried no channel — there is deliberately NO attempt: brokers redeliver and none tracks a delivery count), and runs in declared order ahead of the handler. A behaviour that returns without calling next() short-circuits: the handler never sees the message. A behaviour that throws follows the messaging handler's existing rejection path. The chain wraps SUBSCRIBE handlers only — respond (RPC) is deliberately not chained and not armed in this milestone.

With no behaviours configured, the broker chain is byte-identical to the pre-arm behaviour: no PipelinedBroker decorator is applied at all.

Instance entries are read by the chain at register(); factory entries are resolved in the onInit phase and a throwing factory rejects start() naming MessagingPlugin({ behaviors }) and the entry's index in THIS declared array.

When an entry is a FACTORY, DELIVERY is held until onInit has resolved the whole chain, so no message reaches a handler through a partial one. A broker holding a backlog delivers the moment a consumer attaches, and the gate covers every subscription — this plugin's declared entries and any a later plugin makes imperatively through the resolved broker — which is why no registration's timing has to change. It is released once and costs nothing thereafter.