趋势与波动：什么认得出，什么认不出Market State & Volatility: what holds up, and what does not

三层：先用完整价格路径定义什么才算一段趋势，再看只用历史信息能认出多少，最后逐一测它能拿来做什么。负结果与正结果一样如实列出。Three layers: define what counts as a trend from the full price path, measure how much a strictly causal model recovers, then test what it can actually be used for. Negative results are reported as plainly as positive ones.