/**
 * Task state machine — defines valid transitions and guards.
 *
 * States: created → running | failed | cancelled | timed_out
 *                   running → completed | failed | cancelled | timed_out
 *
 * Terminal states reject all further transitions (first-writer-wins).
 */
import { type TaskState } from './types.js';
/**
 * Check whether a state transition is valid.
 */
export declare function isValidTransition(from: TaskState, to: TaskState): boolean;
/**
 * Check whether a state is terminal (no further transitions).
 */
export declare function isTerminalState(state: TaskState): boolean;
/**
 * Attempt a state transition. Returns the new state on success,
 * or null if the transition is invalid.
 */
export declare function transition(from: TaskState, to: TaskState): TaskState | null;
/**
 * Map from terminal state to a human-readable reason.
 */
export declare const TERMINAL_REASONS: Record<string, string>;
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