@langchain/langgraph/dist/pregel/replay.js

LangGraph

import "../constants.js";
//#region src/pregel/replay.ts
/**
* Tracks subgraph checkpoint loading during parent-graph time travel.
*
* When a parent replays from a historical checkpoint, nested subgraphs must
* load the checkpoint that existed *before* the replay point on their first
* visit, then fall back to normal latest-checkpoint loading on later visits
* within the same run.
*/
var ReplayState = class {
	/** Parent checkpoint ID used as the `before` cursor for subgraph lookups. */
	checkpointId;
	#visitedNs = /* @__PURE__ */ new Set();
	/**
	* @param checkpointId - Checkpoint ID from the parent graph at the replay point.
	*/
	constructor(checkpointId) {
		this.checkpointId = checkpointId;
	}
	/**
	* Whether this is the first visit to a logical subgraph namespace in the run.
	*
	* Task-id suffixes are stripped so the same subgraph invoked across loop
	* iterations shares one visit record.
	*
	* @param checkpointNs - Subgraph checkpoint namespace.
	*/
	#isFirstVisit(checkpointNs) {
		const stableNs = checkpointNs.includes(":") ? checkpointNs.slice(0, checkpointNs.lastIndexOf(":")) : checkpointNs;
		if (this.#visitedNs.has(stableNs)) return false;
		this.#visitedNs.add(stableNs);
		return true;
	}
	/**
	* Load the checkpoint tuple for a subgraph namespace during replay.
	*
	* On the first visit to `checkpointNs`, returns the latest checkpoint saved
	* before {@link ReplayState.checkpointId}. On subsequent visits, delegates to
	* `checkpointer.getTuple` for the current config.
	*
	* @param checkpointNs - Subgraph checkpoint namespace.
	* @param checkpointer - Checkpointer shared with the parent graph.
	* @param checkpointConfig - Runnable config for the subgraph lookup.
	* @returns The resolved checkpoint tuple, if any.
	*/
	async getCheckpoint(checkpointNs, checkpointer, checkpointConfig) {
		if (this.#isFirstVisit(checkpointNs)) {
			const results = [];
			for await (const saved of checkpointer.list(checkpointConfig, {
				before: { configurable: { checkpoint_id: this.checkpointId } },
				limit: 1
			})) results.push(saved);
			return results.length > 0 ? results[0] : void 0;
		}
		return await checkpointer.getTuple(checkpointConfig) ?? void 0;
	}
};
//#endregion
export { ReplayState };

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