The Mask Is Not the Model: Auditing Prefix Invariance in Attention, State-Space, and Hybrid Sequence Models

The mask passed. The scan leaked: an audit finds future tokens reaching back in two shipped hybrids

VIDRAFT's prefix-invariance test reports causal leakage in Nemotron-H-8B and Zamba2-1.2B, starting at chunk sizes of 128 and 256. Mask inspection caught none of 192 injected faults.