import type { SessionEvent } from '../types/session/events.js';
export interface CoalesceOptions {
    /**
     * Sliding merge window. 16ms is roughly one animation frame at 60fps,
     * which is the point past which a human cannot see the difference and
     * below which the consumer pays for deltas nobody perceives.
     */
    windowMs: number;
}
/**
 * Coalesces high-frequency `text_delta` and `tool_input_delta` events into
 * fewer, larger events to relieve downstream backpressure (typically a
 * Server-Sent Events adapter writing to a slow client).
 *
 * Within a sliding `windowMs` window, consecutive `text_delta` events for
 * the same `messageId` are merged by string concatenation; consecutive
 * `tool_input_delta` events for the same `toolUseId` are likewise merged.
 * All other event types pass through immediately and flush any buffered
 * deltas first to preserve ordering.
 *
 * The orchestrator does NOT use this — it emits raw deltas, and nothing
 * inside the kernel calls this function. That is deliberate and is why it
 * is exported: the consumer this exists for is a host's HTTP route, and a
 * kernel with no UI and no hosted service has no in-process caller to
 * offer. `bridge/sse/` maps an event to the wire; deciding how OFTEN to
 * write to a slow client is the host's policy, because only the host
 * knows what is on the other end of its socket.
 *
 * `streaming/` owns coalescing and nothing else. SSE mapping lives in
 * `bridge/sse/`, provider chunk assembly in the provider drivers, and the
 * session event stream in `runtime/query/` — none of them belong here, and a
 * second occupant of this directory should be another rate policy or
 * nothing.
 *
 * Backpressure semantics: this helper does not drop events. If the
 * upstream produces faster than the consumer drains, the helper still
 * yields every coalesced batch; the consumer must apply its own bound or
 * accept queue growth.
 */
export declare function coalesce(stream: AsyncIterable<SessionEvent>, options?: CoalesceOptions): AsyncGenerator<SessionEvent, void, unknown>;
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