Function openOutputFile

src/commands/test.ts:7766–7799

* Open the `--out` target before any network I/O so a permission/dir * error fails fast. Synchronous open via `createWriteStream` doesn't * actually open the descriptor until first write, so we don't surface * EACCES/ENOENT here — instead the stream emits `'error'`, which we * remember on the si

(rawPath: string)

 * on a sandboxed fs, etc.) are caught before the API request goes out.
 */
function openOutputFile(rawPath: string): FileSink {
  if (typeof rawPath !== 'string' || rawPath.length === 0) {
    throw localValidationError('out', 'must be a non-empty file path');
  }
  const resolved = isAbsolute(rawPath) ? rawPath : resolve(process.cwd(), rawPath);
  // Defensive: reject obviously-bad paths up front (a directory string
  // would fail later with EISDIR; that's a clearer 5/VALIDATION_ERROR
  // surface than letting it crash mid-write with TransportError).
  if (resolved.endsWith('/')) {
    throw localValidationError('out', 'must point to a file, not a directory');
  }
  // Validate the parent dir synchronously so a missing or non-directory
  // parent surfaces as exit 5 / VALIDATION_ERROR rather than exit 1 /
  // TRANSPORT_ERROR. Without this, an ENOENT/ENOTDIR fires asynchronously
  // on first write and gets re-raised through `closeOutputFile` as a
  // TransportError — an exit-code mismatch with the rest of `--out`'s
  // input validation.
  const parent = dirname(resolved);
  let parentStat;
  try {
    parentStat = statSync(parent);
  } catch {
    throw localValidationError('out', `parent directory does not exist: ${parent}`);
  }
  if (!parentStat.isDirectory()) {
    throw localValidationError('out', `parent path is not a directory: ${parent}`);
  }
  const stream = createWriteStream(resolved, { encoding: 'utf8' });
  const sink: FileSink = { stream, path: resolved, error: null };
  stream.on('error', err => {
    sink.error = err instanceof Error ? err : new Error(String(err));
  });
  return sink;
}

/**
 * Adapter that turns a `FileSink` into the `Output` writer set. Both