-- Migration 0018: multi-policy scope for discount codes
--
-- Until now, a discount code could be scoped to exactly one policy
-- (`applies_to_policy_id`) or "any policy on this product" / global.
-- That left a real gap: "this code is good for Patron OR Pro but not
-- Creator" required creating two distinct codes with different code
-- strings, which is operationally messy.
--
-- New column `applies_to_policy_ids_json`: a JSON-encoded array of
-- policy ids (TEXT uuids). Semantics:
--
--   NULL or '[]' → no multi-policy restriction. Fall back to the legacy
--                  `applies_to_policy_id` (single-policy scope) or, if
--                  that's also NULL, scope follows `applies_to_product_id`
--                  (or global if that's NULL too). Identical behavior
--                  to v0.2.0:19 and earlier.
--
--   '["id1","id2",...]' → the code applies if and only if the buyer's
--                         chosen policy is in this array. Takes
--                         precedence over `applies_to_policy_id` (the
--                         legacy singular column is ignored when this
--                         is non-empty).
--
-- Migration is purely additive. Existing rows have the new column NULL,
-- so all v0.2.0:19-and-earlier discount codes keep working unchanged.
-- New codes written via the admin API populate this column when the
-- operator picks 2+ policies; single-policy codes continue to write to
-- `applies_to_policy_id` for clarity.

ALTER TABLE discount_codes ADD COLUMN applies_to_policy_ids_json TEXT NULL;