Protocol Adapters

Built-in helpers:

• createJsonTransport
• createGraphqlTransport
• createSseTransport
• createWebSocketSessionTransport
• createGrpcUnaryTransport
• createGrpcStreamTransport
• createGrpcSessionTransport
• createGrpcTransport

Adapter guidance:

• set normalized capabilities explicitly
• preserve request.signal
• use canonical TransportError codes
• publish stream() for progressive output
• publish openSession() only for long-lived channels
• expose session backpressure metadata when relevant

If a protocol does not match a built-in helper, return a plain custom transport.