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

Unlike productUpdate, this mutation's id lives INSIDE the input. The path id is written there for you and OVERRIDES any id in the body, so a caller cannot edit a different collection by accident.

Editing a SMART collection's ruleSet is how you change its membership. Shopify recomputes that asynchronously, so productsCount immediately after can still be the old number — re-read it rather than retrying.

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