Runtime Results API

这些 API 描述 worker attempt 的运行结果，以及异常到 Conductor 状态的映射。

RuntimeTaskResult(*, status[, output, ...])	Validated result payload returned by a worker attempt.
completed_result(output)	Build a completed worker attempt result.
failed_result(reason)	Build a failed worker attempt result.
terminal_failed_result(reason)	Build a terminal failed worker attempt result.
result_for_exception(exc)	Classify an exception into a worker attempt result.