PUH Theorem 287 (Derivation) — The Core Mass Spectrum from Amalgamation-Only Growth: Horizon-Like Cores Force a Coagulation Kernel of Degree 2, Hence Gelation (the Amalgamated Planck Star, Derived Not Assumed) and a Pre-Gel Spectrum with Exponent 5/2; T285's Kill-Condition Is Satisfied | Synapse