/**
 * Constant-time string comparison for credential-shaped values - lease tokens, token hashes, and
 * binding digests.
 *
 * `a !== b` returns as soon as it finds a differing character, so how long it takes reveals how much
 * of a guess was correct. That is only exploitable when an attacker can submit guesses and measure,
 * which is not the case on every path here - but these values are credentials, the comparison is on
 * the verification path, and doing it correctly costs nothing. Doing it inconsistently is what makes
 * the one place that matters easy to miss.
 *
 * Length is compared first, so a length difference is still observable. Every value compared through
 * this helper is fixed-width by construction (a UUID, a SHA-256 hex/base64url digest), so length
 * carries no secret. Content comparison always visits every character.
 *
 * Synchronous on purpose: the callers are store transitions and lease checks that are themselves
 * synchronous. A hash-then-compare variant (which would also hide length) is available as
 * `timingSafeEqualString` in `@nifrajs/middleware`, but it is async and would force those paths async.
 */
export declare function safeEqual(a: string | undefined, b: string | undefined): boolean;
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