Re-Ranking & Business Rules

After the ranker scores items individually, a re-ranking pass treats them as a slate. Slate-level constraints can't be per-item features — 'no more than two items from the same creator' is a statement about the set, not a property of any item.

What lives here:

• Dedup — near-identical items, reposts, same-creator runs
• Diversity caps — per-category, per-seller, per-format limits
• Freshness boosts — time-decayed lifts for new or trending items
• Policy filters — age gates, regional restrictions, rights-managed content

Re-ranking runs on the ~100 items that survived ranking, which is cheap enough to afford combinatorial logic the earlier stages can't.