Surface terminations in multicomponent MXenes are usually treated as chemical decorations of an averaged metal substrate, while metal-layer ordering is treated as a separate configurational problem. Here we show that this separation fails when a termination couples to the local surface–subsurface metal ensemble beneath it. We formulate a boundary-field theory in which termination identity, coverage, and coordination act as local thermodynamic fields on the outer $M\prime$ and inner $M″$ metal layers. Reanalysis of the Wyatt $M_4{AlC}_3\to M_4{C}_3{T}_x$ series [Science , 1054 (2025)] shows that the secondary-ion-mass-spectrometry (SIMS) layer-order strength collapses near seven transition metals, accompanied by a coherent termination drift in which O-rich surfaces increase along the disorder coordinate while OH- and F-rich contributions decrease. A sign-normalized Ti–Mo test further shows that the boundary-field sign depends on both termination and coordination: prismatic O favors Mo-rich outer layers, whereas octahedral O and F favor Ti-rich outer layers. Targeted Ti–Mo slab calculations reproduce this sign pattern and give an O/F switching point $f_{\rm O}^{\star}\simeq0.52$, close to the analytic sign-only prediction $f_{\rm O}^{\star}=0.50$. Independent configuration-level DFT tests give $R_{\rm fixed}^{2}=0.984$ for 20 frozen-prediction segregation energies and inverse Pearson and Spearman correlations of $-0.989$ and $-0.992$, respectively, for 20 fixed-composition registry energies. The resulting reduced model predicts termination-enhanced order, termination-induced inverse order, and compensation lines where the global layer order vanishes. In the grand-canonical extension, chemical potentials and pH-like proton activity transform these compensation lines into hidden-order regimes: the averaged order parameter is small, but termination-resolved local order remains finite. A model-generated descriptor benchmark shows that a valence electron concentration (VEC)-like average scalar fails, while the boundary-field descriptor collapses the ordering data with $R^2\simeq 0.95$. Within the prescribed sign structure (DFT-supported for Ti–Mo/O–F and source-guided for OH/Cl), all ${10}^5$ sign-preserving hypercube samples retain the O/F compensation point, and $94.1\%$ retain termination-resolved order above the sampled visibility threshold.