While Kronecker coefficients $g(λ,μ,ν)$ with bounded rows are polynomial-time computable via lattice-point methods, no explicit closed-form formulas have been obtained for genuinely three-row cases in the 87 years since Murnaghan's foundational work. This paper provides such formulas for the first time and identifies a universal structural boundary at parameter value 5 where elementary combinatorial patterns collapse. We analyze two independent families of genuinely three-row coefficients and establish that for $k \leq 4$, the formulas exhibit elementary structure: oscillation bounds follow the triangular-Hogben pattern, and polynomial expressions factor completely over $\mathbb{Z}$. At the critical threshold $k=5$, this structure collapses: the triangular pattern fails, and algebraic obstructions -- irreducible quadratic factors with negative discriminant -- emerge. We develop integer forcing, a proof technique exploiting the tension between continuous asymptotics and discrete integrality. As concrete results, we prove that $g((n,n,1)^3) = 2 - (n \mod 2)$ for all $n \geq 3$ -- the first explicit formula for a genuinely three-row Kronecker coefficient -- derive five explicit polynomial formulas for staircase-hook coefficients, and verify Saxl's conjecture for 132 three-row partitions.

翻译：尽管具有有界行的Kronecker系数$g(λ,μ,ν)$可通过格点方法在多项式时间内计算，但自Murnaghan奠基性工作以来的87年间，对于真正的三行情况尚未获得显式闭式公式。本文首次提供了此类公式，并确定了参数值5处的普适结构边界，在此处基本组合模式发生坍塌。我们分析了两类独立的真正三行系数族，并证明当$k \leq 4$时，公式呈现基本结构：振荡边界遵循三角-Hogben模式，且多项式表达式在$\mathbb{Z}$上完全分解。在临界阈值$k=5$处，该结构发生坍塌：三角模式失效，且代数障碍——具有负判别式的不可约二次因子——开始出现。我们发展了整数强制技术，这是一种利用连续渐近性与离散整数性之间张力的证明方法。作为具体成果，我们证明了$g((n,n,1)^3) = 2 - (n \mod 2)$对所有$n \geq 3$成立——这是首个真正三行Kronecker系数的显式公式，推导了阶梯钩系数的五个显式多项式公式，并验证了Saxl猜想对132个三行分拆的成立。