Adapter {
    // Translation
    ingest(external: ExternalPayload) -> Result<Signal>
    emit(signal: Signal) -> Result<ExternalPayload>

    // Metadata
    protocol() -> Protocol
    capabilities() -> AdapterCapabilities

    // Lifecycle
    start() -> Result
    stop() -> Result
    health() -> AdapterHealth
}

ExternalPayload {
    data: bytes,              // Raw payload
    content_type: string,     // MIME type
    metadata: Map<string, string>,  // Protocol-specific metadata
}

AdapterCapabilities {
    can_ingest: bool,         // Can receive external → signal
    can_emit: bool,           // Can send signal → external
    bidirectional: bool,      // Supports persistent bidirectional channel
    correlation: bool,        // Supports request-response correlation
    streaming: bool,          // Supports streaming signals
}

node.register_adapter(adapter) -> Result