Propagation-enhanced molecular high-harmonic generation driven by a spatiotemporal vortex field.

High-order harmonic generation (HHG) provides a key route to ultrafast structured radiation, yet how spatiotemporal topology manifests, survives, and builds up in molecular HHG remains largely unexplored. Here, we investigate HHG from aligned O2 molecules driven by a spatiotemporal vortex (STOV) field within a microscopic-macroscopic theoretical framework. We show that the transverse phase structure of the STOV field is transferred to the molecular harmonic radiation, leading to pronounced spatio-spectral tilt and helical phase distributions with transverse-orbital-angular-momentum character. Molecular alignment mainly regulates the harmonic yield while leaving the topology-imprinted spatial structure largely preserved. During macroscopic propagation, coherent buildup substantially enhances the harmonic signal and gives rise to an order-dependent optimum propagation length associated with phase-mismatch accumulation. These results reveal a coherent propagation-enhancement mechanism in molecular HHG and suggest STOV driving as a route toward efficient topology-tailored extreme-ultraviolet emission.