/**
 * Liveness checks for the stdio streams the logging layer writes to.
 *
 * Shared by `StdoutSink` (which stops writing to a dead stream) and the
 * runner's `watchOutputStream` (which stops the loop, and exits only when its
 * caller owns the process), so the two cannot disagree about what "dead" means.
 * See `_devlog/notes/2026-09-07-stdout-epipe-log-loop.md`.
 */
/**
 * Structural subset of `process.stdout` these helpers need. Declared instead of
 * `NodeJS.WriteStream` so tests and embedders can pass an ordinary `Writable`.
 */
export type OutputStream = NodeJS.WritableStream & {
    isTTY?: boolean;
    destroyed?: boolean;
    writableEnded?: boolean;
};
/**
 * True only for `EPIPE` — the reader closed its end.
 *
 * Deliberately narrow, because callers act on it by killing the process: a
 * wider set would let an unrelated bad descriptor take a whole session down.
 * Use {@link isUnwritableStreamError} to decide whether to stop *writing*.
 */
export declare function isBrokenPipeError(err: unknown): boolean;
/** True when a further write to this stream can only fail the same way. */
export declare function isUnwritableStreamError(err: unknown): boolean;
/** False once the stream has been destroyed or ended. */
export declare function isStreamOpen(stream: {
    destroyed?: boolean;
    writableEnded?: boolean;
}): boolean;
/** Record that a stream will never accept another write. Idempotent. */
export declare function markStreamBroken(stream: object): void;
/**
 * Forget every broken-stream mark. Test-only — the registry is process-wide by
 * design, so a suite that breaks a stream would otherwise leak that verdict.
 * @internal
 */
export declare function __resetBrokenStreams(): void;
/** True while a stream is worth writing to. */
export declare function isStreamUsable(stream: {
    destroyed?: boolean;
    writableEnded?: boolean;
}): boolean;
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