Create private discount code applicable only to selected products or collections

User story:

As a merchant, I want to create a private discount code that applies a product-level discount (e.g., 10% off) only to a specified collection or group of products, so that only customers who enter the code at checkout receive the discount and the offer is not visible publicly.

Acceptance criteria / requirements:

• Campaign type: Advanced Discount Code with at least one Product Discount module enabled.

• Discount scope: allow merchant to choose between selecting specific products, variants, or full collections (support selecting multiple collections and/or individual products).

• Code-only activation: the discount must be applied only when the merchant-created discount code is entered at checkout (no automatic public banner or storefront visibility). The campaign is tied to a discount code string.

• Discount types supported: percentage or fixed amount applied to selected items.

• Exclusions: allow exclusion list of products or variants within the selected scope.

• Quantity / requirements: support optional minimum quantity requirement (apply only if required quantity per order is met).

• Scheduling: support start/end dates so code works only within defined window.

• Combination rules: allow choosing whether this campaign can or cannot stack with other campaigns (default: no stacking unless merchant enables combination options).

• Behavior at checkout: when the code is entered, evaluate Product Discount module rules and apply discount only to items in selected products/collections that meet any configured requirements; do not alter other products or apply to entire order unless an Order Discount module is also configured.

Examples:

• Create code SUMMER10: Product Discount = 10% off on collection "Summer Dresses"; active between 2026-06-01 and 2026-06-30; code must be entered to apply.

• Create code VIPSET: Product Discount = $5 off each item in selected SKU list; minimum quantity = 2; code required at checkout.

Notes on mapping to existing logic:

• This maps directly to the existing Product Discount module (Scenario 1.1 / 1.2 / 1.3): scope can be products or variants, optional minimum quantity, and optional exclusions.

• Because Discounty campaigns center on a discount code and modules, a private code that targets collections/products is supported by modeling a Campaign with a Discount Code + Product Discount module configured to 'collections' or selected product list.

Edge cases / validations:

• If merchant selects a collection and that collection is later changed (products added/removed), the campaign should evaluate the current collection membership at checkout.

• Validation to ensure at least one product/collection is selected when Product Discount is enabled.

• Clear UI label that the discount is code-based and will not display publicly unless the merchant chooses to promote it.