/**
 * Race-free output-path writability preflight (neutral, surface-agnostic).
 *
 * Used by every CLI surface that supports `--output <file>` to verify the
 * target path is writable BEFORE doing any side-effecting work (spawning a
 * child process, loading an issuer key, signing, etc.). A record-producing
 * wrapper must never do that work only to discover the record cannot be
 * persisted.
 *
 * The preflight is deliberately non-invasive on the final target path:
 *   - if the final target exists, open it for append/write check and
 *     close it; never unlink the existing target
 *   - if the final target does NOT exist, create a uniquely-named
 *     sibling temp file in the parent directory with O_EXCL and
 *     immediately unlink that temp file; the final target path is
 *     not created or touched until the actual write step
 *
 * Result: between preflight and the eventual write, the CLI has NOT
 * created or modified the final output path. Concurrent observers cannot
 * race against a transient zero-byte target file produced by the preflight.
 */
/**
 * Verify that `--output <file>` will be writable. Returns null on
 * success; otherwise an error message suitable for pairing with
 * `cli.output_write_failed`.
 */
export declare function preflightOutputWritable(output: string): string | null;
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