feat(go.d): support managed metadata for payload-aware functions - #23940

sequenceDiagram
    participant UI as UI Client
    participant AM as Agent Manager
    participant JG as Job Generation
    participant MG as Method Generation
    participant H as Handler
    participant R as Raw Handler
    participant C as Collector

    Note over UI,C: Managed Metadata for Payload-Aware Functions

    UI->>AM: Function request (info)
    AM->>JG: Route to generation
    JG->>MG: handle(info request)

    MG->>MG: Parse args & payload
    
    alt Structured or raw without job selection
        MG->>MG: Return declaration metadata
        MG-->>UI: Info response (no handler call)
    else Raw with managed info and job selection
        MG->>MG: Resolve selected job
        MG->>R: HandleRaw with Info:true
        R-->>MG: RequiredParams + Help
        MG->>MG: Merge metadata & selectors
        MG-->>UI: Scoped info response
    end

    Note over UI,C: Data Request Flow

    UI->>AM: Function request (data + __job)
    AM->>JG: Route to generation
    JG->>MG: handle(data request)

    MG->>MG: Parse args & payload
    MG->>MG: Resolve target job
    
    alt Structured method
        MG->>H: MethodParams + Handle
        H-->>MG: FunctionResponse
    else Raw method
        MG->>R: HandleRaw (preserve payload)
        R-->>MG: FunctionResponse
    end

    alt Managed info requested
        MG->>MG: Include metadata only
    else Data response
        MG->>MG: Include columns & data
    end
    
    MG-->>UI: Composed response

    Note over MG,H: Validation and Failures
    
    alt Invalid declaration (ManagedInfo without RawRequest)
        MG-->>UI: 400 error
    else Unknown job or multiple jobs
        MG-->>UI: 4xx error
    else Job stopped during request
        MG-->>UI: 503 error
    end