Corrected Interaction Calculus for the Residual Erdős–Straus Obstruction: Weighted Snowflake Defects, Split-Zero Positivity, Niemeier Glue, and Modular Support Resolution

This note replaces the object-list presentation of the residual Erdős–Straus framework by a single interacting calculus. For a hard prime class p ≡ 289ᵏ (mod 840) and a residual shell R ≡ 3 (mod 4), the fixed-shell divisor equation is first projectively normalized, producing the invariant target −1. The missing structure is then restored by the six-sector coordinate C₆ ≅ C₃ × C₂, so that the two normalized targets are not merely an unordered pair but the weighted snowflake defect 𝔇ₖ = E_{−k, −(−1)ᵏ} + 2E_{−k, −(−1)ᵏ} ∈ ℤ[C₃ × C₂]. The coefficient 2 is forced by the two p-origins in divisors of p²a². Certificate existence is proved equivalent to positivity of the split-zero pullback count Ω_R(p) = 𝔠̃_R(a; −1) + 2𝔠̃_R(a; −p⁻¹). The target defect has full Fourier support for every k, so a persistent obstruction cannot come from target degeneracy; it can only come from bounded positive-mass failure of the signed divisor box. The champion prime p∗ = 8,803,369 realizes the strict ladder (τ, τ) → (0_ℤ, 0_ℤ) → (2, 0_ℤ) for R = 27, 43, 107. The same full-arm sign reversal is resolved by the modular critical arm 744 ↔ 747 ↔ 750: the raw A₈³ eta sheet vanishes on all three points, while Fricke and Eisenstein channels separate the negative endpoint, the supported-zero hub, and the positive endpoint. We compute the nonlinear A₈³ support resolvent, the linear lambency-six A₅⁴D₄ resolvents, and the finite transport matrices P₉→₆⁽ⁱ⁾ over 𝔽₁₀₇, including their characteristic polynomials. The note also records the exact A₅⁴D₄ glue datum of order 72 and the non-split GL₂(3) symmetry, only insofar as these objects act in the positivity calculus.