Plugin-level ingress behaviours wrapped around every route's onMessage — the WebSocket arm of the transport-neutral behaviour chain shared with the queue, scheduler, and messaging plugins (IIngressBehavior in @setu-ts/common).

Each behaviour observes an IngressContext carrying kind: 'websocket', the route path as name, and the frame as payload, and runs in declared order ahead of the handler. A behaviour that returns without calling next() short-circuits: the handler never sees the frame. A behaviour that throws is routed to the route's onError, exactly as a failing handler is. Behaviours are plugin-level by design; there is no route-level behaviors arm (guards are the per-route mechanism).

Configuring a behaviour makes the dispatch result promise-mediated while preserving immediate execution for entirely synchronous behaviours. A behaviour that defers next() delays the wrapped handler. With no behaviours configured, dispatch is byte-identical to the pre-chain behaviour: a direct, synchronous invoke.

No startup gate is needed here, unlike the queue, scheduler, and messaging arms: a frame cannot arrive before its socket is open, and the application does not serve until after onInit has resolved the chain.

Instance entries are handed to the service at register(); factory entries are resolved in the onInit phase and a throwing factory rejects start() naming WebSocketPlugin({ behaviors }) and the entry's index in THIS declared array.