RfreeFlagsTest: determinism (pure function of the reflection), ~5% free fraction,
Friedel/Bijvoet pairs never split, symmetry equivalents share a flag, resolution
stratification (free set spans shells), and fraction=0 flags nothing.
FrenchWilsonTest: strong reflections reduce to sqrt(I), weak/negative intensities get
a positive amplitude, amplitudes are always finite and non-negative (incl. centric /
epsilon>1 reflections in P4(3)2(1)2), and unusable sigma falls back to sqrt(max(I,0)).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
