How touching a quantum boundary turns entanglement into steering

Entanglement and quantum steering are distinct resources, but this paper shows that when Bob's conditional states graze the surface of the Bloch sphere at just the right angle, entanglement automatically upgrades to steering. The mechanism is purely geometric: a specific mismatch between tangential drift and inward curvature at that boundary contact blocks any classical explanation. The result certifies that entire families of two-qubit states — including all entangled rank-two states — are provably steerable, with the boundary-contact condition serving as a compact experimental witness.