Modeling 2026 US East Coast Statutory Tax Cliffs in OpenAPI 3.1 & MCP (NY LLC § 206, NYC CEMA § 255 & Estate Cliffs)

In algorithmic financial modeling, the most expensive engineering bugs do not stem from floating-point roundoff errors; they originate from treating statutory tax functions as continuous rather than piecewise discontinuous manifolds. Across the 16-state US East Coast corridor (Maine to Florida), real-world state and municipal codes contain abrupt statutory cliffs where a single dollar of additional valuation or modified adjusted gross income (MAGI) triggers non-marginal, retroactive liability steps. At the East Corp Capital Open Data & API Desk, we standardize these state-level statutory discontinuities into machine-readable OpenAPI 3.1.0 specifications and Model Context Protocol (MCP) toolkits. Below is an engineering overview of how to model these non-linear structures cleanly in vanilla JavaScript and expose them across LLM agent architectures. 1. The Anatomy of a Statutory Discontinuity A classic progressive income tax operates via marginal brackets: $$\text{Tax}(x) = \sum_{i=1}^n \tau_i \cdot \max(0, \min(x - k_{i-1}, k_i - k_{i-1}))$$ Statutory cliffs, however, introduce step-function indicator multipliers $\mathbb{I}_{x > T}$: A. The New York Estate Tax "105% Marginal Cliff" (NY Tax Law § 952) New York allows a basic exclusion amount of $7,160,000 in 2026. However, if the taxable estate exceeds 105% of this threshold ($7,518,000), the entire exemption is retroactively eliminated. At $7,160,001, marginal tax rates theoretically exceed 100%, creating an infamous financial trap modeled in our NY $7.16M Estate Tax Cliff & Santa Clause Calculator. B. NYC CEMA § 255 Mortgage Recording Tax Consolidation Under NY Tax Law § 255, a Consolidation, Extension, and Modification Agreement (CEMA) allows a refinancer or property purchaser to pay Mortgage Recording Tax (MRT) only on the new money rather than the total principal. In NYC, where the combined MRT reaches 1.925% (under $500k) or 2.80% (over $500k), failing to isolate statutory base credits costs borrowers tens of thousands of dollars. We quantify these exact spreads in the NYC Mansion Tax & CEMA § 255 Closing Cost Calculator. C. NY LLC Section 206 Albany Publication Arbitrage Under NY LLC Law § 206, newly formed limited liability companies must publish notices in two designated county newspapers for six consecutive weeks. In New York County (Manhattan), publisher rates and county clerk designations routinely exceed $1,400 to $1,650. Moving the registered office via Certificate of Change to Albany County caps total costs at $215 ($25 state filing + $140 newspapers + $50 Certificate of Publication), an arbitrage detailed in our NY LLC Section 206 Albany Publication Arbitrage Calculator (2026). 2. Dependency-Free JavaScript Modeling Here is a production snippet modeling the 2026 NY Estate Cliff and Medicare Part B IRMAA cliff without external libraries: /** * Calculates 2026 NY Estate Tax Cliff under NY Tax Law § 952. * Retroactive forfeiture occurs between 100% and 105% of exclusion. */ function calculateNYEstateTax2026(estateValue) { const EXCLUSION_2026 = 7160000; const CLIFF_THRESHOLD = EXCLUSION_2026 * 1.05; // $7,518,000 if (estateValue EXCLUSION_2026 && estateValue CLIFF_THRESHOLD) ? estateValue : (estateValue - EXCLUSION_2026); // Progressive state brackets (5.06% to 16.0%) const stateBrackets = [ { limit: 500000, rate: 0.0506 }, { limit: 1000000, rate: 0.055 }, { limit: 1500000, rate: 0.065 }, { limit: 2100000, rate: 0.080 }, { limit: 7100000, rate: 0.128 }, { limit: Infinity, rate: 0.160 } ]; let accumulatedTax = 0; let remaining = isTrap ? estateValue : (estateValue - EXCLUSION_2026); let previousLimit = 0; for (const b of stateBrackets) { const chunk = Math.min(Math.max(0, remaining), b.limit - previousLimit); accumulatedTax += chunk * b.rate; remaining -= chunk; previousLimit = b.limit; if (remaining