EDGES reported a 21-cm absorption trough at z near 17 twice as deep as standard thermodynamics permits (Bowman 2018), requiring gas colder than adiabatic or a Cosmic Dawn radio background brighter than the CMB, while SARAS 3 failed to confirm the profile (Singh 2022). The tension is double: EDGES against theory, and EDGES against SARAS 3.
The model fixes both sides of the trough: gas cools adiabatically and the only backlight is the CMB, capping absorption near -230 mK. A deeper signal needs dark-matter-baryon scattering or early radio sources, the first exotic and the second absent from the standard inventory, which built no radio-luminous population that early.
SCT does not need the trough to choose its physics, because the framework independently supplies the less exotic of the two options: a Cosmic Dawn radio background brighter than the CMB alone. The cascade-seeded compact-object population radiates from the earliest epochs (P46, P25), the same undercounted demography invoked, on separate evidence, for the ARCADE 2 radio background excess (recid 159); a seeded population bright enough to leave today's unexplained low-frequency glow was necessarily radiating at z of 17, deepening any 21-cm absorption against it. If EDGES is real, its depth is the high-redshift face of the radio excess already measured at low redshift, two anomalies triangulating one seeded population, with no dark-matter-baryon scattering required.
The framework keeps its bets honest on the experimental question: if SARAS 3 is right and EDGES instrumental, SCT loses nothing, since the seeded radio background stands on ARCADE 2 and the demography arguments independently. What SCT registers is the conditional: any confirmed global-signal depth beyond the adiabatic cap should be accounted for by excess backlight, not modified gas thermodynamics, a discriminant the next-generation experiments can test by measuring the trough's shape, since backlight and cold-gas mechanisms deform the profile differently. The seeding mechanics are in Paper 4, From Chaos To Collisothermal Cosmogenesis, with the staggered ionization context at recid 170.
Keystone economy: P46 supplies the backlight; the trough, if real, is its shadow.
The discriminant is registered: if REACH, MIST, or lunar-farside experiments confirm a deep trough whose profile shape demands cold-gas thermodynamics rather than excess backlight, dark-matter-baryon scattering signatures rather than radio-background ones, the seeded-backlight reading fails. Symmetrically, 21-cm results establishing that no radio background above the CMB existed at Cosmic Dawn would contradict the early-radiating seeded population that the ARCADE 2 sector independently requires.