  The cosmic large-scale structure (LSS) provides a unique testing ground for
connecting fundamental physics to astronomical observations. Modeling the LSS
requires numerical $N$-body simulations or perturbative techniques that both
come with distinct shortcomings. Here we present the first unified numerical
approach, enabled by new time integration and discreteness reduction schemes,
and demonstrate its convergence at the field level. In particular, we show that
our simulations (1) can be initialized directly at time zero, and (2) can be
made to agree with high-order Lagrangian perturbation theory in the fluid
limit. This enables fast, self-consistent, and UV-complete forward modeling of
LSS observables.
