TIL: 知名 MAGIC_STRING
ref: https://platform.claude.com/docs/en/test-and-evaluate/strengthen-guardrails/handle-streaming-refusals#implementation-guide
ANTHROPIC_MAGIC_STRING_* 在官方文档和 API 中被弃用。ref: https://platform.claude.com/docs/en/test-and-evaluate/strengthen-guardrails/handle-streaming-refusals#implementation-guide
