  Binary neutron stars have been observed as millisecond pulsars,
gravitational-wave sources, and as the progenitors of short gamma-ray bursts
and kilonovae. Massive stellar binaries that evolve into merging double neutron
stars are believed to experience a common-envelope episode. During this
episode, the envelope of a giant star engulfs the whole binary. The energy
transferred from the orbit to the envelope by drag forces or from other energy
sources can eject the envelope from the binary system, leading to a stripped
short-period binary. In this paper, we use one-dimensional single stellar
evolution to explore the final stages of the common-envelope phase in
progenitors of neutron star binaries. We consider an instantaneously stripped
donor star as a proxy for the common-envelope phase and study the star's
subsequent radial evolution. We determine a range of stripping boundaries which
allow the star to avoid significant rapid re-expansion and which thus represent
plausible boundaries for the termination of the common-envelope episode. We
find that these boundaries lie above the maximum compression point, a commonly
used location of the core/envelope boundary. We conclude that stars may retain
fractions of a solar mass of hydrogen-rich material even after the
common-envelope episode. If we consider orbital energy as the only energy
source available, all of our models would overfill their Roche lobe after
ejecting the envelope, whose binding energy includes gravitational, thermal,
radiation, and recombination energy terms.
