Radio relics trace cluster shocks whose X-ray and SZ Mach numbers, 1.5 to 3, are too weak for diffusive shock acceleration to light them: thermal-pool injection falls short by orders of magnitude, with several relics demanding efficiencies over 100 percent. The repair, ubiquitous fossil electrons from past AGN, must blanket megaparsec arcs at cluster outskirts where bubbles rarely travel, and LOFAR keeps finding relics in quiet systems that deepen the demand.
The model's relativistic-electron ledger starts empty: seeds must be manufactured by identifiable AGN activity and transported to where the shocks are. The relic census requires a seed population more widespread, older, and better distributed than the model's injection bookkeeping supplies, so the fossils are postulated where needed.
SCT fills the seed ledger structurally: the intracluster medium is collision-deposited material that was thermalized by shocks at birth (P22, P25), carrying relic non-thermal tails alongside its relic entropy, and the deep seeded compact-object census (P46) populates cluster volumes with old accelerators whose integrated relativistic output exceeds the catalogued-AGN bookkeeping. Fossil electrons blanketing megaparsec peripheries are not a per-relic rescue but the default condition of deposited plasma: weak merger shocks then re-energize cheaply everywhere, which is why relics are common, why they appear in undisturbed systems, and why most arcs trace to no identifiable source. The coherent mesh adds the secondary layer: amplified peripheral fields (inherited flux compressed at deposition boundaries, P33) raise synchrotron yield where the standard dynamo arrives late.
Halos ride the same inventory with the quiescence problem resolved alongside: the measured ICM calm (the non-thermal pressure entry) starves turbulent re-acceleration in the standard story, but a richer fossil floor needs less stirring, letting modest gas motions sustain halos that ΛCDM's turbulence budget cannot.
This is the same deposited-inventory physics behind the entropy floors and the quiet cores, read in synchrotron. There is no need for fossil reservoirs to be postulated arc by arc; the deposition stocked them.
The seed census is becoming measurable: LOFAR and SKA spectral mapping that traces relic seed populations and finds them strictly localized to identifiable AGN lobes, absent elsewhere, with relic incidence tracking catalogued injection history rather than a universal floor, would remove the deposited-fossil reading. Equally, relics fully explained by revised Mach numbers (X-ray biases resolving the efficiency gap) would retire the tension and the mechanism with it.