Matter–Antimatter Progenitor Encounter as an Inflation Trigger, with Post-Inflation BAU Closure

This note is a standalone construction inside standard physics: Trigger (pre‑FRW): a matter–antimatter progenitor encounter that produces a high‑energy burst. The encounter is not analyzed with FRW thermodynamics; it is used only to motivate and justify an initial‑condition selection for the subsequent FRW patch. Inflation (FRW window): an NEC‑respecting FRW inflationary window whose kinematics are fixed by a single ledger parameter Θ and anchored to the observed late‑time closure term Λ_post. Matter–antimatter asymmetry (post‑inflation): the observed baryon asymmetry is closed deterministically by adopting the minimal mainstream completion: Type‑I thermal leptogenesis with reheating temperature T_R ≳ 10^9 GeV. No modified gravity, no exotic horizon thermodynamics, and no inflaton model‑building are introduced. All quantitative outputs follow from standard identities plus the declared throat ratio Θ.