A Conditional K3 Fibonacci Scalar in the A_diag-Local Sector

We give a scoped manuscript version of the local derivation recorded in the Alpha-Ladder K3 Fibonacci Graviton Closure artifacts. The result is not that the ordinary unit-normalized K3 slot-5 graviton amplitude equals φ/2. That ordinary branch remains negative in the local slot-5 calculation. The result is instead conditional: given the AGHV Fibonacci topological defect line at the (3)²(8) K3 Gepner point as an unbroken categorical symmetry input, and defining the protected screened observable in the Boundary-SymTFT A_diag-local-module boundary, the local M-sector does not survive as an independent local protected observable, the surviving P-sector is nonzero, and the BPS scalar is P_BPS(⟨Ω_g Ω_g⟩cubic) = Tr{V^τττ}(−Re Θ_τ) / dim V^τττ = φ/2. The paper also records the main review surface: the mathematical arithmetic of φ/2 is standard; what is not proved is that the ordinary K3 graviton vertex is physically forced into this condensed observable. The result should therefore be read as a conditional or defined-observable theorem for the A_diag-screened sector.