We present Vacuum Flux Cosmology (VFC), a classical framework in which early-universe expansion emerges from a geometric transition across a finite hypersurface. Governed by Einstein’s equations and the Israel junction conditions, this transition enables a curvature-induced redistribution of vacuum energy from a preceding collapsing phase, offering a possible non-singular extension of early-universe dynamics within general relativity. Rather than a time-reversed contraction, the process is a geometric phase change, with spacetime evolving across a boundary interface without invoking time symmetry or exotic fields. The model incorporates a high-temperature quark-gluon plasma phase and derives expansion from general relativity and thermodynamics. VFC is formulated as a minimal, extensible baseline for cosmogenesis, providing a classical foundation that can integrate with or support broader theoretical frameworks.