The all-weights-zero branch of ChooseProduct and the required-item fallback of RandomProducts weighed
every product 1, so a bin doubled its maker's presence there. Both now weigh by Share alone (the
preference drops out, the bins' shares do not). The sum of a line's bins' pass fractions is computed
once per weighting pass instead of scanning the product table per candidate.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>