Mirrors Admin GraphQL collectionCreate. Body: { input: CollectionInput }.

OMIT ruleSet for a CUSTOM (manual) collection; PASS it for a SMART one. The choice is fixed at creation and determines whether collections/{id}/products works at all.

The new collection is UNPUBLISHED, exactly like a new product — publish it with publishablePublish or it stays invisible to customers.

• Write — changes a live store immediately; needs a write-scoped token.