1
Why global pruning is brittle. One static importance ranking is an average over everything, so under a new scenario the wrong heads get cut.
2
Subspace–pathway coupling. DBS builds near-orthogonal domain axes; PSP maps them — via probes, head importance, and a whitelist — to a budgeted head mask.
3
That it works and is cheap. Pruned beats dense on Qwen2.5-14B (47.8 / 44.1 / 31.3), with online compilation in 0.027–0.068s, reused every turn.