Narrow product promotion boundary (`generate/derivation/product_bridge.py`)
wired into `generate/math_candidate_graph.py`: only complete pure-product
derivations with a product-target question and no known hazard surface lift
from the sealed pooled derivation reader into serving.
- Serving train_sample: 4/46/0 → 6/44/0, wrong=0; case 0050 still refused.
- Renumbered from the collided ADR-0194 (labeled-container, #499) to ADR-0195
and rebased onto current main.
CI: smoke + verify-pinned-lane-SHAs green on the merge commit.
