The dwarf satellites of the Milky Way, Andromeda, and other nearby hosts are not distributed as nearly isotropic swarms, but instead show striking phase-space correlations: many lie in thin, co-rotating planes, form close kinematic pairs, or are strongly lopsided and oriented towards a companion galaxy, patterns that appear exceedingly rare in ΛCDM simulations where satellite subhalos are expected to occupy more random or transient configurations (Kroupa et al. 2005; Pawlowski 2018). This mismatch between the observed, long-lived, kinematically coherent satellite structures and the more chaotic, only briefly planar subhalo systems produced in state-of-the-art ΛCDM runs has led to the “planes-of-satellites” and broader satellite phase-space problems, which remain debated small-scale challenges to the standard cosmological model (Ibata et al. 2013; Pawlowski 2021).