Robustness seed 16 failed in most runs: the imprint split a block's side along both halves of a cylinder's round side, and the second split re-traced the first circle, sometimes leaving a sliver the glue could not match. The imprint now splits along each surface once (10/10 runs pass, 3/12 before). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>