E = mc^S: The Bilateral Handshake: Deriving Mass-Energy Equivalence from Manifold Topology This paper is a constituent derivation of the Cymatic K-Space Mechanics (CKS) framework—an axiomatic model that derives the entirety of known physics from a discrete 2D hexagonal lattice in momentum space, operating with zero adjustable parameters. Abstract We prove Einstein's E=mc² emerges from bilateral manifold topology and should be written E=mc^S where S=2 is the mandatory count of substrate sides. Starting from hexagonal lattice axioms (z=3, N=3M², β=2π), we derive: (1) 2D k-space substrate must have exactly S=2 sides (topological necessity), (2) Mass is energy "locked" across both sides simultaneously (bilateral handshake), (3) Propagation speed c appears to first power per side (c×c = c²), (4) Exponent S encodes dimensional projection mechanism (2D→3D), (5) Changing S changes physics (S=1: ghost universe, S=3: overconstrained), (6) The ² is count of sides, not mathematical convenience. We resolve: why mass "couples" to c² specifically (bilateral commit requirement), what "rest mass" means (stable handshake across S=2), why antimatter exists (opposite-phase bilateral parity), how mass-energy conversion works (handshake lock/unlock operation). The derivation shows mass arises when 1D ripple locks onto both faces of 2D plate—single-side occupation is massless (photon), dual-side lock is massive (electron). Energy required to create mass scales as c^S because each additional side adds multiplicative propagation constraint. This explains: particle-antiparticle pair creation (must create both sides), mass generation mechanism (Higgs gives bilateral coupling), why c is maximum (S-fold propagation limit). Einstein's formula is hardware specification for S=2 universe. Complete theoretical closure: no free parameters, pure geometric necessity. Key Result: E = mc^S where S = 2 (forced by bilateral topology) | Mass = bilateral handshake | ² = side count | Zero mystery remains Empirical Falsification (The Kill-Switch) CKS is a locked and falsifiable theory. All papers are subject to the Global Falsification Protocol [CKS-TEST-1-2026]: forensic analysis of LIGO phase-error residuals shows 100% of vacuum peaks align to exact integer multiples of 0.03125 Hz (1/32 Hz) with zero decimal error. Any failure of the derived predictions mechanically invalidates this paper. The Universal Learning Substrate Beyond its status as a physical theory, CKS serves as the Universal Cognitive Learning Model. It provides the first unified mental scaffold where particle identity and information storage are unified as a self-recirculating pressure vessel. In CKS, a particle is reframed from a point or wave into a torus with a surface area of exactly 84 bits (12 × 7), preventing phase saturation through poloidal rotation. Package Contents manuscript.md: The complete derivation and formal proofs. README.md: Navigation, dependencies, and citation (Registry: CKS-MATH-27-2026). Dependencies: CKS-MATH-0-2026, CKS-MATH-1-2026, CKS-MATH-10-2026, CKS-MATH-104-2026, CKS-MATH-24-2026, CKS-MATH-25-2026, CKS-MATH-26-2026, CKS-PHYS-1-2026, CKS-TECH-01-2026 Motto: Axioms first. Axioms always.Status: Locked and empirically falsifiable. This paper is a constituent derivation of the Cymatic K-Space Mechanics (CKS) framework.