/**
 * A shared budget for held-open SSE connections (ADR 0032 §6).
 *
 * The live endpoints and the conditional-subscription stream (#311) are the
 * same kind of resource: a socket the collector keeps open, a subscriber on an
 * in-process bus, and a heartbeat timer. `LIVE_MAX_CONNECTIONS` is meant to
 * bound *that*, so they draw on one counter rather than one each — otherwise the
 * setting silently means "up to 2 × max", and grows every time another SSE
 * surface is added.
 */
export interface ConnectionLimiter {
    /** Take a slot, or `false` when the budget is exhausted. */
    acquire(): boolean;
    /** Return a slot. Never drops below zero, so a double release is harmless. */
    release(): void;
    /** Slots currently held (for tests). */
    readonly open: number;
    /** The configured ceiling. */
    readonly max: number;
}
/** Create a limiter over `max` concurrent connections. */
export declare function createConnectionLimiter(max: number): ConnectionLimiter;
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