/**
 * Rich HTML error pages for `dev` mode (stack, Error.cause chain, non-Error serialization).
 */
/** Message, stack, optional cause chain, and JSON for plain objects. */
export declare function collectErrorDetails(err: unknown): {
    message: string;
    stack: string;
    causes: string[];
    plain: string;
};
/**
 * Full diagnostic page in dev; minimal safe page when `dev` is false.
 */
export declare function devErrorHtmlPage(opts: {
    context: string;
    err: unknown;
    dev: boolean;
}): string;
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