/**
 * Browser-safe, zero-dependency loopback classification shared by the `/api`
 * Host fence and the package's `ctx.connection` state. The predicate stays
 * package-internal; client plugins consume the derived state through Cordis.
 */
/**
 * Whether a normalized URL hostname names the local loopback authority.
 * @param hostname - WHATWG URL hostname (IPv6 literals retain brackets).
 * @returns true for localhost, IPv6 loopback, or any IPv4 address in 127/8.
 */
export declare function isLoopbackHostname(hostname: string): boolean;
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