Foundational Companion — The Pentagon Theorem: Why There Are Exactly Three Lepton Generations Papers I–VI establish that the condensate predicts three lepton generations through three independent routes: the fine structure constant selects k = 3, the Verlinde formula gives the golden ratio as a quantum dimension, and the WZW primary truncation excludes a fourth generation. This paper shows that all three routes are the same statement in disguise. The single equation behind all three is: k + 2 = 5 where k = 3 is the WZW level and 5 is the number of sides of the regular pentagon — the face of the dodecahedron dual to the icosahedron that underlies the condensate’s symmetry group 2I. The Pentagon Theorem proves that k = 3 is the unique positive integer consistent with the condensate framework, via three independent exclusions: k ≠ 3 is excluded by QED at ~1.5 × 107 sigma by the four-term fine-structure-constant formula. k = 3 is the unique level at which the muon primary has quantum dimension φ = 2cos(π/5), the pentagon diagonal-to-side ratio. A fourth lepton generation would require a primary j = 2 > k/2 = 3/2, which does not exist in the SU(2)3 WZW model. This is a hard algebraic non-existence statement, independent of all numerical inputs. The three non-vacuum primaries (j = 1/2, 1, 3/2) are filled by the three non-real Hurwitz division algebras ℂ, ℍ, 𝓞. Their termination at the octonions mirrors the primary truncation at j = 3/2: the next algebra (sedenions) loses alternativity, just as the next primary would require j = 2 > k/2. The quark generation count is addressed and resolved: it follows from E8 Coxeter exponent saturation (Paper V), not from the Pentagon Theorem. The two mechanisms are complementary within the same 2I/Ê8 structure. The Pentagon Theorem is a complete and closed statement about leptons.