EDGE event: price touches/crosses a band edge (Bollinger, Keltner, Donchian) — fires on the touch / cross_in / cross_out bar. USE WHEN you want one-shot trigger on the boundary event. DO NOT USE when you want every bar price is outside the band — use 'band_level' for that level/state semantics. Sub-field band requires {band:bollinger|keltner|donchian|vwap_band, length:int, mult:float=2.0}. Aliases: period→length, std→mult. Note: std_dev is NOT accepted — use mult. Example band: {"band":"bollinger","length":20,"mult":2}