[econ] some invention stats

apps/econ/migrations/0026_invention_num_downloads.sql

@@ -0,0 +1,20 @@
+-- An invention's `NumDownloads` is the number of players who have it: the rows in
+-- `inventory_invention` that name it. `grantInvention` now re-derives it on every grant
+-- (packages/domain/src/inventory-invention-db.ts); every purchase before that left it at
+-- the 0 a save mints, so this backfills the inventions already bought.
+--
+-- The `invention` table is the `api` worker's (same database). `ModifiedAt` is left alone:
+-- being bought is not an edit of the invention.
+
+-- Backs that per-invention count; the primary key leads with account_id.
+-- Generated from INVENTORY_INVENTION_SCHEMA_DDL — keep in sync.
+CREATE INDEX IF NOT EXISTS idx_inventory_invention_invention
+  ON inventory_invention (invention_id);
+
+UPDATE invention
+SET data = json_set(
+  data,
+  '$.NumDownloads',
+  (SELECT COUNT(*) FROM inventory_invention WHERE invention_id = invention.id)
+)
+WHERE id IN (SELECT invention_id FROM inventory_invention);