Search & Discovery complementary products are picked one SKU at a time, so new items ship with an empty Pair it with block. This app maps living collection, tag, or product_type sources to a complement collection or tag. Dry-run, apply, undo the last write, then watch drift as products and pools change. You still own S&D config. Theme checklist only — no theme extension. No AI recs, no cart upsell. Shopify cap is 10. Max 5 rules. First rule wins. Prefer in-stock; exclude self, gifts, drafts.

• Map collection, tag, or product_type sources to a complement collection or tag.
• Dry-run current vs proposed complementary lists before you apply writes.
• Apply fills the native complementary metafield; undo restores the last list.
• Drift shows matching products with empty or stale complementary lists.
• Theme checklist only — add the Complementary products block yourself.