Well-intentioned interventions frequently worsen the crises they seek to prevent: financial rescues can amplify systemic risk; organizational restructurings trigger departure cascades; ecological management interventions push ecosystems past tipping points. This empirical regularity — observed across management science, ecology, and financial economics under names such as the change paradox, intervention-induced tipping, and signaling-induced contagion — has lacked a unified structural explanation. This paper provides that unifying mechanism within a coarse-grained potential model. Systems operating near self-tuned criticality (Paper I of the DFG Trilogy) reside in shallow potential wells V(X) = −AX² + B_pot·X⁴ whose barrier height vanishes at the critical manifold: ΔV ~ |ξ| → 0 as ξ → 0, since A ~ |ξ|^{1/2}. Direct interventions above a magnitude threshold act as energy injections enabling Kramers escape over the barrier — triggering the very cascade they aimed to prevent. Theorem 1 (Intervention Paradox): Above D_threshold, the probability of collapse increases monotonically with intervention magnitude within the model. The stochastic operational threshold D_threshold = 2·sqrt(A·B_pot)·G(X_c)·σ_η shrinks as D_threshold ~ |ξ|^{1/4} → 0 as the system approaches criticality — meaning the safe intervention window collapses precisely when crises appear most imminent. Two distinct threshold formulas are derived from the same Kramers escape framework under different noise-scaling assumptions: D_geom = A²/(4B_pot·|X_c|) is the barrier-elimination criterion in the ungated zero-noise limit (G = 1); D_threshold is the stochastic operational threshold incorporating noise amplification through the logistic gating function G(X_c) = 1/2. D_threshold is interpreted as a phenomenological scaling ansatz — a rigorous Fokker-Planck derivation under non-conservative forcing is identified as future work. Theorem 2 (Buffer-First Principle): Buffer depth increases are monotonically stabilizing within the coarse-grained model class for all Δb > 0: d(ΔV)/d(Δb) > 0. Buffer investment unconditionally deepens the potential well and expands the safe intervention window, making it categorically superior to direct state forcing near criticality. Recommended Three-Phase Governance Protocol (Corollary of Theorems 1–2): (1) maximize buffer depth b first, (2) apply bounded direct intervention ||U|| ≤ D_threshold, (3) transition to structural steering if ξ persists. The rationale follows directly from Theorems 1 and 2; the protocol is not formally proved optimal. Key scaling relations near criticality (A ~ |ξ|^{1/2}, mean-field): Barrier height: ΔV ~ |ξ| → 0 Well minimum: X_c ~ |ξ|^{1/4} → 0 Geometric threshold: D_geom ~ |ξ|^{3/4} → 0 Stochastic threshold: D_threshold ~ |ξ|^{1/4} → 0 (D_threshold > σ_η². Near criticality (ΔV → 0), the system enters a crossover regime where classical Kramers asymptotics break down; the analysis is therefore a scaling argument indicating that intervention-induced barrier reduction accelerates transitions, not an exact escape-rate formula. The qualitative conclusion D_threshold → 0 as ξ → 0 is robust to this limitation. The effective potential V_eff(X) = V(X) − G(X)·U·X is a first-order approximation near the well minimum; U is not a conservative force. The Buffer-First unconditional claim holds within the model class only. The order parameter X is related to the critical coordinate ξ of Paper I through a smooth reparameterization X = f(ξ) with f(0) = 0, representing the normal-form reduction of the coordination dynamics near the bifurcation point and formalizing the connection between the GGT critical coordinate and the double-well potential structure. This paper is Series Paper III of the Deficit-Fractal Governance (DFG) Framework. Together with Paper I (self-tuned criticality) and Paper II (cascade universality), it completes the trilogy: critical coordination systems simultaneously generate universal power-law cascades, restrict safe intervention magnitude to zero at criticality, and require logarithmic hierarchy depth — three structural consequences of the same coordination balance Γ ≈ Γ_c.