eh not the prettiest, but visits is just an increment and we might have others later. room_columns is not user-provided

apps/rooms/migrations/0011_room_visits.sql

@@ -0,0 +1,17 @@
+-- Lifetime visit counter on `room`. The `match` worker bumps it once per successful
+-- matchmake into the room (see recordRoomVisit, called from match's enterRoom), which
+-- is the only way a player ever lands in a room, and every room read serves it as the
+-- room's `Stats.VisitCount`.
+--
+-- A real column rather than a field in the `data` blob: a visit has to be one atomic
+-- `visits = visits + 1` UPDATE. Writing it into the blob would mean reading the whole
+-- room, editing the JSON and writing it back, so two players entering at once would
+-- lose one of the visits — and would race every other writer of the room besides.
+--
+-- Unlike CheerCount/FavoriteCount it can't be derived on read either: a visit leaves
+-- no per-player row to count (`interaction.last_visited_at` is only stamped by the
+-- cheer/favorite toggles). Existing rooms start from 0 — the count begins now.
+--
+-- Generated from packages/domain/src/rooms-db.ts (ROOM_SCHEMA_DDL) — keep in sync.
+
+ALTER TABLE room ADD COLUMN visits INTEGER NOT NULL DEFAULT 0;