Test-only opt-in. New shear_twin.py: same two L0->L1 boxes as
shear_nested, no L2; leaves [7936,33792], hops [2048,4096], work
154664960. Four fresh cases U128/U256/constant R128 d2/projected R128 d2;
physics is the unchanged depth-2/2N shear_wave.assess. run_case:
--diagnostic twin_shear_n128 with shear_twin.py+shear_nested.py pins, no
snapshot. assess_shear_wave: nested contract made preset-generic (PRESETS)
with nested behaviour unchanged. Labels: twin vs nested = effect of adding
this nested refinement (not abstract depth). shear_wave.py, shear_nested.py
and oracle.py byte-identical.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>