Fast blue optical transients like AT2018cow rise in days, stay hot and blue, and keep radiating engine-driven X-rays and radio long after radioactive transients fade (Margutti 2019; Coppejans 2020). Every standard channel fails a requirement: core collapse is too slow, TDEs are misplaced, IMBH disruptions need an unestablished population, and tuned magnetars must not overproduce ordinary events (Perley 2019).
The model's transient inventory is closed: every engine must descend from standard stellar evolution or from the SMBHs that hierarchical growth placed in galactic nuclei. FBOTs demand compact engines in low-mass ejecta at off-nuclear sites in dwarf hosts, a combination the closed inventory can only assemble by borrowing or tuning.
SCT's transient inventory was never closed. The cascade seeded compact objects directly, dense deposit regions collapsing into black holes and degenerate remnants across a mass spectrum set by collision geometry rather than by stellar evolution (P46), and the matter it organized included structures inherited from prior cycles (P25, P28). The population implied is exactly what FBOTs require and the standard inventory lacks: intermediate-mass and unconventional compact objects distributed through galaxies rather than confined to nuclei, available off-center and in dwarf hosts, with no stellar-evolution pedigree to violate. An AT2018cow-class event, a compact engine disrupting or accreting low-mass material at an off-nuclear site, is a natural encounter within that seeded population.
This is the same cascade-seeded inventory already carrying the overmassive high-z black holes (recid 109) and the early quenched nuclei, read here in the time domain: the seeding that puts 10⁹ M☉ engines at z of 7 also scatters smaller engines through low-mass hosts at z of 0. The registered population-level signature follows: FBOT hosts and locations should track the deposited compact-object distribution, dwarf-rich and radially extended, rather than the nuclear and star-formation-weighted maps standard engines predict. The seeding mechanics are in Paper 4, From Chaos To Collisothermal Cosmogenesis, with the compact-object framework in Paper 9, From Chaos To Collapse Proof.
Keystone economy: P46 stocks the inventory, P25 supplies the fuel. The taxonomy broke because the inventory was bigger than the taxonomy.
Rubin-era statistics carry the kill: if the multiplied FBOT census resolves cleanly into tuned standard channels, rates, hosts, and engine signatures all matching stellar-evolution or nuclear-TDE expectations with no residual population, the seeded-inventory reading is unnecessary. SCT separately requires the off-nuclear engine population to exist independently: deep X-ray and dynamical searches finding no intermediate-mass compact objects outside nuclei, at the abundance the FBOT rate implies, would refute the cascade-seeded distribution directly.