/**
 * Formats a string for error messages, truncating above the threshold.
 * When the PUNCTILIO_DEBUG environment variable is set to a non-empty
 * value, also writes the full content to stderr in Node.js so build logs
 * capture it.
 */
export declare function formatErrorString(content: string, label: string): string;
/** Throws if `options` contains a key not present in `validKeys`. @internal */
export declare function assertKnownOptionKeys(options: object, validKeys: readonly string[], context: string): void;
/** Returns a copy of `obj` without the listed keys. @internal */
export declare function omitKeys<T extends object>(obj: T, keys: readonly string[]): Partial<T>;
/** Returns a copy of `obj` with `undefined`-valued keys removed. @internal */
export declare function filterUndefined<T extends object>(obj: T): Partial<T>;
/** Deterministic JSON string for an options object, suitable as cache key. @internal */
export declare function stableStringify(obj: object): string;
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