Allergen + dietary flags, kosher / GF / vegan / nut-free. How do you handle catalog filtering?

Gourmet customers filter aggressively by diet. A gluten-free customer who lands on a charcuterie page that doesn’t filter clearly will bounce in seconds. The pattern I ship:

• Allergen attribute set, multi-select Magento attribute: contains-gluten, contains-dairy, contains-nuts, contains-soy, contains-eggs, contains-shellfish, contains-pork. Per-SKU, populated from supplier spec sheets. Surfaces as filter facets on category pages.
• Dietary-certification attribute set, multi-select: kosher (OU / OK / Star-K), halal, vegan, vegetarian, gluten-free (GFCO certified vs naturally GF), organic (USDA / EU), keto, paleo. Each certification has its badge icon on PDP + listing pages.
• PDP allergen panel, required Magento block on every food PDP, color-coded (red for contains, green for free-of). FDA Food Allergen Labeling Act compliance baked in.
• Cross-contact warning, for SKUs produced in a facility that handles nuts/dairy but the SKU itself doesn’t contain them. Separate attribute with mandatory disclosure text.

Catalog filtering: Hyvä category-page filters need to support multi-select faceting (a gluten-free + nut-free + vegan filter set narrows the catalog to qualifying SKUs). Native Magento layered nav handles this; Hyvä accelerates it client-side after the first paint.

Edge case: kosher-for-passover. Some SKUs are kosher year-round but not Passover-kosher (chametz). Needs a seasonal attribute that auto-flips its filter visibility in March-April.