Function: parseA2ARequest()

function parseA2ARequest(payload: unknown): 
  | {
  id: string | number | null;
  jsonrpc: "2.0";
  method: "tasks/send";
  params: {
     acceptedOutputModes?: string[] | null;
     historyLength?: number | null;
     id: string;
     message: {
        metadata?: Metadata | null;
        parts: (
           | {
           metadata?: Metadata | null;
           text: string;
           type: "text";
         }
           | {
           file: {
              bytes?: string | null;
              mimeType?: string | null;
              name?: string | null;
              uri?: string | null;
           };
           metadata?: Metadata | null;
           type: "file";
         }
           | {
           data: Metadata;
           metadata?: Metadata | null;
           type: "data";
        })[];
        role: "user" | "agent";
     };
     metadata?: Metadata | null;
     pushNotification?:   | {
        authentication?:   | {
         [key: string]: unknown;
           credentials?: string | null;
           schemes: string[];
         }
           | null;
        token?: string | null;
        url: string;
      }
        | null;
     sessionId: string;
  };
}
  | {
  id: string | number | null;
  jsonrpc: "2.0";
  method: "tasks/get";
  params: {
     historyLength?: number | null;
     id: string;
     metadata?: Metadata | null;
  };
}
  | {
  id: string | number | null;
  jsonrpc: "2.0";
  method: "tasks/cancel";
  params: {
     id: string;
     metadata?: Metadata | null;
  };
}
  | {
  id: string | number | null;
  jsonrpc: "2.0";
  method: "tasks/pushNotification/set";
  params: {
     id: string;
     pushNotificationConfig: {
        authentication?:   | {
         [key: string]: unknown;
           credentials?: string | null;
           schemes: string[];
         }
           | null;
        token?: string | null;
        url: string;
     };
  };
}
  | {
  id: string | number | null;
  jsonrpc: "2.0";
  method: "tasks/pushNotification/get";
  params: {
     id: string;
     metadata?: Metadata | null;
  };
}
  | {
  id: string | number | null;
  jsonrpc: "2.0";
  method: "tasks/resubscribe";
  params: {
     id: string;
     metadata?: Metadata | null;
  };
}
  | {
  id: string | number | null;
  jsonrpc: "2.0";
  method: "tasks/sendSubscribe";
  params: {
     acceptedOutputModes?: string[] | null;
     historyLength?: number | null;
     id: string;
     message: {
        metadata?: Metadata | null;
        parts: (
           | {
           metadata?: Metadata | null;
           text: string;
           type: "text";
         }
           | {
           file: {
              bytes?: string | null;
              mimeType?: string | null;
              name?: string | null;
              uri?: string | null;
           };
           metadata?: Metadata | null;
           type: "file";
         }
           | {
           data: Metadata;
           metadata?: Metadata | null;
           type: "data";
        })[];
        role: "user" | "agent";
     };
     metadata?: Metadata | null;
     pushNotification?:   | {
        authentication?:   | {
         [key: string]: unknown;
           credentials?: string | null;
           schemes: string[];
         }
           | null;
        token?: string | null;
        url: string;
      }
        | null;
     sessionId: string;
  };
}
  | {
  id: string | number | null;
  jsonrpc: "2.0";
  method: "tasks/sendUnsubscribe";
  params: {
     id: string;
     metadata?: Metadata | null;
  };
}
  | {
  id: string | number | null;
  jsonrpc: "2.0";
  method: "agent.get_card";
  params: Record<string, never>;
};