Boundary Obstructions and Lapse Freedom in Static Spherical Hollow Cores

We analyze a sharply delimited comparison problem for a static spherical hollow core: an empty, flat cavity surrounded by a positive matter wall. In the unit-lapse, flat-slice radial Painleve--Gullstrand (PG) class the Type-I source obeys $p_r=-\rho$ and $p_\perp=-\rho-r\rho'/2$. A regular nonnegative density that rises out of the cavity must therefore violate the transverse null and weak energy conditions. We quantify this boundary obstruction by an exact weighted onset budget and a depth--width bound, and show that the sharp limit has the same negative tangential pressure as its symmetry-invariant regularized Israel layer. We then close the adjacent unit-lapse, curved-slice route under a monotone areal-radius hypothesis. Finally, when only the lapse is released, an incomplete-beta family gives regular hollow shells with flat cavities, Schwarzschild exteriors, no thin shells, and NEC/WEC/SEC/DEC on an explicit compactness interval. The family is conditionally characterized in the minimum-degree and $p_r=0$ sectors and admits a fixed-ADM-mass cavity redshift benchmark. The result is a static boundary theorem and construction, not a general hollow-shell existence theorem, a transport result, or an experimental feasibility claim.