/**
 * Resolve a stable client key from proxy headers.
 *
 * Forwarded headers are ignored unless proxy trust is explicit. When trusted,
 * use the rightmost X-Forwarded-For value, which is the address appended by the
 * nearest proxy, then fall back to X-Real-IP.
 */
export declare function resolveRateLimitClientKey(request: Request, trustProxy: boolean, fallback: string): string;
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