/**
 * Engine-backed `WorkflowEventFeedBackend` — the production backing
 * for `createWorkflowEventFeed` (see `workflow-event-feed.ts`). REST
 * SSE, the JSON-RPC WebSocket session, and the JSON-RPC stdio session
 * all consume the feed; this module is where the feed meets the
 * `Engine`'s durable state.
 *
 * **Single committed sequence authority.** Replay and live delivery
 * share the same source of truth — the unified
 * `replayWorkflowFeed` / `snapshotWorkflowFeedTail` /
 * `subscribeWorkflowFeedCommits` triple on `Engine`. The subscription
 * fires only AFTER the storage commit resolves, so an event in the live buffer
 * is already durable and scannable by `replayWorkflowFeed`. This is the
 * invariant the feed's atomic-handoff (buffer-then-snapshot-then-replay-then-
 * drain) relies on.
 *
 * The backend is intentionally stateless — it holds only the `Engine`
 * reference. Listener state lives on the engine and is cleaned up by
 * the caller's unsubscribe function.
 *
 * @module server/engine-event-feed-backend
 */
import type { RegistryAgnosticEngine } from '../core/engine.ts';
import { type WorkflowEventFeedBackend } from './workflow-event-feed.ts';
/**
 * Build the production `WorkflowEventFeedBackend`. Call once per
 * engine instance and share the returned backend across every
 * transport that needs a feed. Pass the result to `createWorkflowEventFeed()`
 * to build a `WorkflowEventFeed` for `HandlerOptions.workflowEventFeed`.
 *
 * Accepts `RegistryAgnosticEngine` — the same registry-erased engine type
 * `handleRequest()` and `ServeOptions.engine` accept — so a concretely
 * narrowed engine from `Engine.create({ workflows })` works here without a
 * call-site cast.
 *
 * @example
 * ```ts
 * import { Engine, MemoryStorage } from '@lostgradient/weft';
 * import {
 *   createEngineEventFeedBackend,
 *   createWorkflowEventFeed,
 * } from '@lostgradient/weft/server/handler';
 *
 * const engine = new Engine({ storage: new MemoryStorage() });
 * const workflowEventFeed = createWorkflowEventFeed(createEngineEventFeedBackend(engine));
 * void workflowEventFeed;
 * ```
 */
export declare function createEngineEventFeedBackend(engine: RegistryAgnosticEngine): WorkflowEventFeedBackend;