/**
 * Multi-session Orchestration, Session Task Graph
 *
 * Implements the in-memory cross-session task graph with:
 * - Global task reference registration and status propagation
 * - Dependency edge tracking
 * - Handoff record management
 * - Subtree traversal for scoped cancellation
 * - Snapshot serialization for reconnect/resume consistency
 */
import type { CrossSessionTaskRef, TaskHandoffRecord, CancellationRequest, CancellationResult, SessionTaskGraphSnapshot } from './types.js';
import type { TaskLifecycleState } from '../../runtime/store/domains/tasks.js';
/**
 * SessionTaskGraph, the central in-memory cross-session task graph.
 *
 * All mutations are synchronous and produce no external side effects,
 * callers are responsible for persisting snapshots via SessionTaskGraphRegistry.
 *
 * Invariants:
 * - Ref keys are unique per (sessionId, taskId) pair.
 * - Edges reference only registered refs.
 * - Handoff IDs are globally unique within the graph lifetime.
 * - The graph is acyclic (cycle detection is performed on `addEdge`).
 */
export declare class SessionTaskGraph {
    /** Primary ref store keyed by makeRefKey(sessionId, taskId). */
    private readonly _refs;
    /** Dependency edges: fromKey → Set<toKey> */
    private readonly _deps;
    /** Reverse edges: toKey → Set<fromKey> (dependents of a given task). */
    private readonly _rdeps;
    /** Handoff records keyed by handoffId. */
    private readonly _handoffs;
    /** All stored edges in insertion order for snapshot serialization. */
    private readonly _edgeList;
    /**
     * Register a new cross-session task ref or update an existing one.
     *
     * If a ref with the same key already exists, only mutable fields
     * (status, updatedAt, label) are patched, immutable identity fields
     * (sessionId, taskId, createdAt) are preserved.
     *
     * @param ref - The ref to register or update.
     * @returns The ref as stored (after any patch).
     */
    upsertRef(ref: CrossSessionTaskRef): CrossSessionTaskRef;
    /**
     * Retrieve a ref by session + task ID.
     *
     * @returns The ref if found, or `undefined`.
     */
    getRef(sessionId: string, taskId: string): CrossSessionTaskRef | undefined;
    /**
     * Return all refs owned by a given session.
     *
     * @param sessionId - The owning session ID.
     * @returns Array of refs (may be empty).
     */
    getRefsBySession(sessionId: string): CrossSessionTaskRef[];
    /**
     * Return all currently registered refs.
     */
    getAllRefs(): CrossSessionTaskRef[];
    /**
     * Propagate a status update to a ref.
     *
     * Idempotent: updating to the same status is a no-op.
     *
     * @param sessionId - Owning session.
     * @param taskId - Target task.
     * @param status - New lifecycle status.
     * @returns `true` if the status changed; `false` if ref not found or no change.
     */
    propagateStatus(sessionId: string, taskId: string, status: TaskLifecycleState): boolean;
    /**
     * Add a dependency edge: `from` depends on `to`.
     *
     * Both refs must already be registered. Adding a duplicate edge is a no-op.
     *
     * @param from - The dependent task.
     * @param to - The dependency.
     * @param reason - Optional human-readable reason.
     * @returns `{ ok: true }` on success, `{ ok: false, error }` on failure.
     */
    addEdge(from: {
        sessionId: string;
        taskId: string;
    }, to: {
        sessionId: string;
        taskId: string;
    }, reason?: string): {
        ok: boolean;
        error?: string;
    };
    /**
     * Returns all direct dependencies of a task (tasks it depends on).
     *
     * @param sessionId - Owning session.
     * @param taskId - Target task.
     * @returns Array of refs this task depends on.
     */
    getDependencies(sessionId: string, taskId: string): CrossSessionTaskRef[];
    /**
     * Returns all direct dependents of a task (tasks that depend on it).
     *
     * @param sessionId - Owning session.
     * @param taskId - Target task.
     * @returns Array of refs that depend on this task.
     */
    getDependents(sessionId: string, taskId: string): CrossSessionTaskRef[];
    /**
     * Collect all refs in the transitive dependent subtree of a task
     * (the task itself plus all tasks that transitively depend on it).
     *
     * Used for `subtree` scoped cancellation.
     *
     * @param sessionId - Root session.
     * @param taskId - Root task.
     * @returns Array of refs in BFS order, root first.
     */
    collectSubtree(sessionId: string, taskId: string): CrossSessionTaskRef[];
    /**
     * Record a task handoff between sessions.
     *
     * @param record - The handoff to record.
     */
    recordHandoff(record: TaskHandoffRecord): void;
    /**
     * Acknowledge a handoff (mark it as received by the destination session).
     *
     * @param handoffId - The handoff to acknowledge.
     * @returns `true` if found and updated; `false` if not found.
     */
    acknowledgeHandoff(handoffId: string): boolean;
    /**
     * Returns all handoff records.
     */
    getHandoffs(): TaskHandoffRecord[];
    /**
     * Returns handoffs targeting or originating from a given session.
     *
     * @param sessionId - The session to filter by.
     */
    getHandoffsForSession(sessionId: string): TaskHandoffRecord[];
    /**
     * Apply a scoped cancellation request to the graph.
     *
     * Updates the status of all targeted refs to 'cancelled'. This method
     * only mutates the in-memory graph, the caller is responsible for
     * propagating the cancellation to the actual task managers.
     *
     * @param request - The cancellation request.
     * @returns Result describing what was cancelled and what was skipped.
     */
    applyCancellation(request: CancellationRequest): CancellationResult;
    /**
     * Take a snapshot of the current graph state for persistence or display.
     *
     * @returns A `SessionTaskGraphSnapshot` with all refs, edges, and handoffs.
     */
    snapshot(): SessionTaskGraphSnapshot;
    /**
     * Hydrate the graph from a persisted snapshot.
     *
     * Existing in-memory state is preserved; snapshot entries are upserted.
     * This allows safe re-hydration on reconnect/resume without data loss.
     *
     * @param snap - The snapshot to hydrate from.
     */
    hydrate(snap: SessionTaskGraphSnapshot): void;
    /**
     * BFS check: is there any path from `startKey` to `targetKey`?
     * Used for cycle detection before adding a new edge.
     */
    private _pathExists;
    /**
     * Resolve a set of ref keys to their corresponding CrossSessionTaskRef objects.
     * Skips keys that are no longer present in the map.
     */
    private _refsForKeys;
}
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