[econ] room consumable token/currency purchase

apps/econ/migrations/0029_room_inventory_concurrency.sql

@@ -0,0 +1,13 @@
+-- What a player holds of a room consumable now remembers its last write: `concurrency_code`
+-- (the request's `NewConcurrencyCode`) and `modified_at`. Owned by the `econ` worker; generated
+-- from src/room-consumable-db.ts (ROOM_INVENTORY_SCHEMA_DDL, which mirrors the table as it
+-- stands AFTER this migration) — keep in sync.
+--
+-- Both are served on the client's `RoomConsumableInventoryItem` (`GET
+-- …/roomConsumable/room/{roomId}/me`, and the purchase's `InventoryItem`) as `ConcurrencyCode`
+-- and `ModifiedAt`. The code is stored to be echoed, not checked — no optimistic concurrency is
+-- implemented. Nullable: rows written before this have neither, and are served a null code and
+-- the listing's own `ModifiedAt`.
+ALTER TABLE room_inventory ADD COLUMN concurrency_code TEXT;
+
+ALTER TABLE room_inventory ADD COLUMN modified_at TEXT;