class AppError(Exception):
    """Domain error used by services to return canonical API errors."""

    def __init__(
        self,
        code: str,
        message: str,
        details: dict | list | None = None,
        status_code: int = 400,
    ) -> None:
        super().__init__(message)
        self.code = code
        self.message = message
        self.details = details or {}
        self.status_code = status_code