Ultra-diffuse galaxies (UDGs, M_star ~ 10⁷ to 10⁸ M☉ spread across 1.5 to 4.5 kpc half-light radii) preferentially trace cosmic-web filaments rather than being isotropically distributed even after group-clustering is accounted for (van Dokkum 2015; Roman 2019; Lim 2018; Mancera Piña 2019). UDGs form coherent streams along filament axes with surface-brightness gradients fading along the stream direction. The pattern has no natural origin in ΛCDM UDG-formation channels.
The standard model treats UDG formation as one of several local processes (high-spin halos, failed L* progenitors, tidal stripping, bursty feedback). None predicts coherent filament-aligned streams across multiple groups. The observed alignment has nowhere to go except as a survey-selection bias or as an unmodeled formation channel.
SCT replaces the hot-dense-center with a superluminal collision and the thermalized debris field. From this single change, cosmic-web filaments are direct geometric products of cascade-stream propagation (P22, P34). Galaxies that form within those filaments inherit the bulk angular momentum J = μ(b × v_rel) of the stream from the cascade impact-parameter geometry (P31, P32). UDG-class galaxies in particular form preferentially within filament environments because the cascade-stream context provides exactly the high-J, low-density conditions that produce UDG morphology.
Stream alignment along filament axes is therefore a predicted signature of the cosmic-web's cascade-stream origin. The surface-brightness gradient fading along the stream direction reflects the progressive thinning of the cascade-stream debris field as it propagates outward from cascade nodes. Pre-existing matter from prior cascade cycles (P25) gives differential star-formation efficiency along the stream as the cascade-debris baryon density gradient produces the observed UDG luminosity gradient. Sibling-pocket gravitational coupling at 10 to 30 Mpc separations (P58, P59, P60) extends the coherence to multi-group scales, producing the observed inter-group UDG stream alignment.
The same M3 + M9 framework that produces the cosmic-filament J-vector inheritance, the satellite-plane co-rotation around hosts, the cluster spin axes perpendicular to filaments, and the quasar polarization 1 Gpc coherence produces the UDG stream alignment. There is no need to invoke new UDG-formation channels or to propose unmodeled survey-selection biases.
If wide-field UDG surveys (LSST + Euclid + Roman) finds UDG distributions consistent with isotropy after careful accounting for group-clustering and selection effects (no filament-stream alignment at the 1% level above isotropy), the M3 cascade-stream explanation is refuted. The signature SCT prediction is coherent UDG streams aligned with filament J vectors, with surface-brightness gradients fading toward stream peripheries.