/**
 * In-memory min-heap that tracks inflight task deadlines.
 *
 * Used by the visibility timeout scanner to avoid a full storage scan
 * on every tick. The scanner pops expired entries from the heap instead
 * of iterating all `op:inflight:*` records.
 *
 * Uses generation-based lazy deletion: each operation ID has a generation
 * counter. `remove()` bumps the generation in O(1), and heap entries with
 * an older generation are skipped during `popMin()` and `drainExpired()`.
 *
 * @module server/deadline-tracker
 */
/** A single tracked deadline entry. */
export type DeadlineEntry = {
    operationId: string;
    deadline: number;
};
/**
 * Min-heap ordered by deadline with O(1) lazy removal.
 *
 * - `add`: O(log n)
 * - `remove`: O(1) — bumps generation counter
 * - `popMin`: O(log n) amortized — skips stale entries
 * - `drainExpired`: O(k log n) where k is the number of expired entries
 */
export declare class DeadlineTracker {
    #private;
    constructor();
    /** Number of tracked deadlines (excludes stale entries). */
    get size(): number;
    /** Peek at the earliest non-stale deadline. Returns `undefined` if empty. */
    peekDeadline(): number | undefined;
    /**
     * Add a new deadline entry. Any previous entry for this operation ID
     * becomes stale and will be skipped during pop/drain.
     */
    add(entry: DeadlineEntry): void;
    /** Remove and return the entry with the earliest deadline, or `undefined` if empty. */
    popMin(): DeadlineEntry | undefined;
    /** Invalidate all entries for the given operation ID in O(1). */
    remove(operationId: string): void;
    /** Drain all non-stale entries whose deadline is at or before `now`. */
    drainExpired(now: number): DeadlineEntry[];
    /** Remove all entries. */
    clear(): void;
}