Function error

Returns {
    _meta?: {
        "io.modelcontextprotocol/related-task"?: { taskId: string };
        progressToken?: string | number;
        [key: string]: unknown;
    };
    content: (
        | {
            _meta?: { [key: string]: unknown };
            annotations?: {
                audience?: ("user" | "assistant")[];
                lastModified?: string;
                priority?: number;
            };
            text: string;
            type: "text";
        }
        | {
            _meta?: { [key: string]: unknown };
            annotations?: {
                audience?: ("user" | "assistant")[];
                lastModified?: string;
                priority?: number;
            };
            data: string;
            mimeType: string;
            type: "image";
        }
        | {
            _meta?: { [key: string]: unknown };
            annotations?: {
                audience?: ("user" | "assistant")[];
                lastModified?: string;
                priority?: number;
            };
            data: string;
            mimeType: string;
            type: "audio";
        }
        | {
            _meta?: { [key: string]: unknown };
            annotations?: {
                audience?: ("user" | "assistant")[];
                lastModified?: string;
                priority?: number;
            };
            description?: string;
            icons?: {
                mimeType?: string;
                sizes?: string[];
                src: string;
                theme?: "light"
                | "dark";
            }[];
            mimeType?: string;
            name: string;
            title?: string;
            type: "resource_link";
            uri: string;
        }
        | {
            _meta?: { [key: string]: unknown };
            annotations?: {
                audience?: ("user" | "assistant")[];
                lastModified?: string;
                priority?: number;
            };
            resource: | {
                _meta?: { [key: string]: unknown };
                mimeType?: string;
                text: string;
                uri: string;
            }
            | {
                _meta?: { [key: string]: unknown };
                blob: string;
                mimeType?: string;
                uri: string;
            };
            type: "resource";
        }
    )[];
    isError?: boolean;
    structuredContent?: { [key: string]: unknown };
    [key: string]: unknown;
}

A CallToolResult with isError=true

// Simple error
return error('Container not found');

// With annotations
return error('Permission denied', {
  annotations: { audience: ['user'] },
});
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