Gravitational-entanglement tests would lie above a composition-dependent collapse threshold

A null witness in gravity-mediated entanglement tests need not mean that gravity is classical. We propose a collapse model in which a split body holds its mass in several places only up to a fixed limit. The limit sets a composition-dependent critical mass, $2.5\times10^{-17}$ kg for carbon, and the proposed diamonds are 40 to 400 times heavier. Each would lose its spin contrast, nulling the witness for a reason unrelated to gravity. Contrast kept by one diamond at the proposed mass and splitting would refute the model, and a Stern-Gerlach chip spanning the threshold would see it vanish as a step