Fast blue optical transients (FBOTs) such as AT2018cow rise to extreme luminosities in only a few days, stay very blue, and often show long-lived, variable X-ray and radio emission, implying compact, engine-driven shocks in very low-mass ejecta moving at mildly relativistic speeds (Margutti et al. 2019; Coppejans et al. 2020). In ΛCDM’s standard stellar-evolution and supernova framework, reproducing simultaneously the short rise time, high optical luminosity, persistent high-energy emission, and sometimes off-nuclear locations without overproducing such events or requiring finely tuned progenitor cocoons and jet geometries remains difficult, so FBOT shock properties are an active tension point for conventional core-collapse and tidal-disruption models (Perley et al. 2019; Lyutikov & Toonen 2022).