Structural topology optimization methods based on phase-field formulations have gained increasing attention as an alternative to classical density-based (SIMP), level-set, or thermodynamically consistent approaches due to their clearer interpretability, comparatively simpler numerical treatment, and systematic formulation. In particular, Cahn–Hilliard models have been successfully applied to topology optimization as they describe the evolution of material distribution while conserving mass by construction and boundary conditions. However, physical bounds on the phase-field variable ( \rho \in [0,1] ) must still be enforced at the discrete level. All numerical schemes in this work are formulated within a purely variational framework so that the complete discrete problem derives from a single functional. This yields a symmetric tangent operator and sufficient smoothness to be solved with a standard Newton algorithm, achieving approximately quadratic convergence and about 50% reduction in computational cost with respect to non-variational implementations. The variational structure also enables further analysis, including inf–sup conditions, Γ-convergence, and stability studies, and is directly generalizable to other phase-field applications such as fracture and multiphysics coupling. Although implicit Euler time discretization and standard finite elements are used, the bound-enforcement strategies are independent of the particular time and space discretizations adopted. Despite the extensive literature on phase-field and PDE-constrained optimization, only a few bound-enforcement techniques have been formulated in weak form, and even fewer incorporated into a discrete variational functional. Here, both classical and newly proposed fully variational bound-enforcement techniques for Cahn–Hilliard topology optimization are implemented and tested on the MBB beam benchmark. Strategies including penalty and barrier methods, reparameterization, Lagrange multipliers with Fischer–Burmeister complementarity functions, and proximal algorithms are compared. To the authors’ knowledge, this is the first work that gathers, reformulates, and compares bound-enforcement techniques within a discrete variational framework for phase-field topology optimization.