/**
 * The words a caller attached to a stop, or nothing when there were none.
 *
 * A cancellation and a deadline arrive by the same mechanism and mean opposite
 * things to whoever reads the result. "Was cancelled" tells a model that
 * something outside it decided, and nothing about what — so a tool result
 * could not distinguish an operator pressing stop from a budget running out
 * from a parent abandoning a child, and every one of those wants a different
 * next move.
 *
 * Two kinds of reason are deliberately reported as no reason:
 *
 * - `AbortError` and `TimeoutError`. `abort()` with no argument fills `reason`
 *   with a DOMException named `AbortError`, so it is not a message anybody
 *   wrote; it is the platform's word for "someone stopped and said nothing".
 *   Rendering it would turn today's honest silence into a fake explanation.
 * - Anything that is not an `Error`. The agent manager aborts a child with the
 *   bare string `'canceled'`, which would otherwise render as "was cancelled:
 *   canceled" — noise wearing the shape of information.
 *
 * Name-checked rather than checked by class, because a reason can cross a
 * package boundary where `instanceof` stops holding across duplicate copies.
 * That is the same answer this codebase already settled on for provider
 * errors.
 */
export declare function abortReasonText(reason: unknown): string | undefined;
/**
 * Subscribe to caller cancellation without raising the Node 20.0 runtime floor.
 *
 * `addAbortListener` cannot be hidden by another listener calling
 * `stopImmediatePropagation`. Both branches return an explicit disposer so a
 * completed operation does not remain attached to a long-lived caller signal.
 */
export declare function subscribeToAbort(signal: AbortSignal, listener: () => void): () => void;
export declare function createChildAbortController(parent: AbortController): AbortController;
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