Patch footprint beat model price: the clearest signal in 60 coding-agent runs

The strongest predictor in a 60-run local-vs-cloud coding-agent benchmark wasn't model quality or price — it was patch footprint. Four-plus-file changes fell to 3/7 held-out checks on every route, including the lane that cost 25x more per run. Decomposition, not a bigger model, is the intervention.