A discount code can now apply to a subset of policies on a product
(e.g. "Patron and Pro but not Creator") instead of being limited to
exactly one policy or the entire product.
- Migration 0018 adds `applies_to_policy_ids_json` (nullable JSON array
of policy ids). Legacy `applies_to_policy_id` stays as the singular
fallback when the JSON column is empty/NULL.
- `DiscountCode::allowed_policy_ids()` helper unifies multi + singular
into one Vec. Purchase + preview scope checks consult it.
- `find_applicable_featured_discount` now narrows multi-policy
candidates in Rust (small candidate set; index-friendly SQL would
require json_each, deferred).
- Admin API: `POST /v1/admin/discount-codes` accepts `policy_slugs`
(array) alongside the existing `policy_slug` (singular). Multi wins
when both are present. PATCH does not allow scope edits — same rule
as the singular field (disable + recreate to re-scope).
- UI: pill multi-select replaces the policy dropdown on the create
form. Edit modal's scope label renders the comma-separated list.
UI + schema both back-compat: existing codes keep working unchanged.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Grant