  Understanding the properties of supercooled fluids in equilibrium, even below
the calorimetric glass transition $T_g$, is an elusive challenge. This is even
more true for the properties of the ideal glass, defined as the minimum of the
potential energy landscape (PEL) in the non-crystalline regime. Although its
existence is a mathematical necessity due to the finite range of energies, its
properties, and physical relevance are still undecided. Here we combine the
million-fold acceleration of Swap Monte Carlo with PEL analysis to study a
non-network 2D model glass former in equilibrium for a wide range of system
sizes and temperatures. We observe the transition from fragile to strong
behavior and provide a generic perspective to such observations in many
experimental non-network glass formers, or the saturation of structural
disorder upon cooling. Furthermore, we can identify a particular system size
that shows quantitative agreement with the macroscopic limit, while allowing a
complete characterization of the potential energy landscape (PEL) down to its
global minimum. This implies the availability of configurational entropy down
to the zero temperature limit without the detour via liquid entropy, thereby
quantifying the putative entropy crisis. Through appropriate system size
analysis, we can identify a low-energy depletion regime, including the ideal
glass, and reveal its physical relevance for equilibrium properties over a wide
temperature range, including below $T_g$.
