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How many powers of ten of tail refinement the constraint grid carries.
This matches the verification grid rather than being coarsened with the interior. The interior of a metalog quantile function is smooth, so constraints there can be sparse, but the tails are where a derivative sign change hides, and a constraint grid that stops short of the verification depth leaves the solver blind to exactly the region the checker will look at. Tail points cost two per decade, so matching is nearly free.