[rooms] fix room instance index

apps/rooms/migrations/0022_room_instance_unique_indexes.sql

@@ -0,0 +1,26 @@
+-- Restore the two UNIQUE indexes on `room_instance`.
+--
+-- Generated from packages/domain/src/room-instance-db.ts (ROOM_INSTANCE_SCHEMA_DDL) —
+-- keep in sync. The DDL and migration 0004 have always declared them, but the deployed
+-- table carried only the non-unique `idx_room_instance_room_id`: the two `CREATE UNIQUE
+-- INDEX` statements never took, so nothing has enforced uniqueness on `id` or
+-- `photon_room_id` in production. Two rows sharing one `photon_room_id` were found —
+-- the signature of a replayed INSERT (same blob written twice), which the index would
+-- have refused. Without the `id` index the `MAX(id) + 1` allocation in
+-- createRoomInstance can also hand two concurrent matchmakes the same id, which the
+-- index would have failed loudly instead of silently minting two instances.
+--
+-- A UNIQUE index refuses to build over duplicates, so they're removed first. Instances
+-- are live sessions, not records: of each duplicate set the earliest row (lowest rowid)
+-- is kept and the rest dropped. A replayed insert's twins are identical, so nothing is
+-- lost; presence rows point at instances by `id`, which the survivor still carries.
+-- Dedupe by `id` first so a row that is a duplicate on both counts is only counted once.
+
+DELETE FROM room_instance
+ WHERE rowid NOT IN (SELECT MIN(rowid) FROM room_instance GROUP BY id);
+
+DELETE FROM room_instance
+ WHERE rowid NOT IN (SELECT MIN(rowid) FROM room_instance GROUP BY photon_room_id);
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_room_instance_id ON room_instance (id);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_room_instance_photon_room_id ON room_instance (photon_room_id);