[api] improve relationships query

apps/api/migrations/0030_relationship_friend_index.sql

@@ -0,0 +1,25 @@
+-- Cover the friend-list read (`getFriendIds` in @repo/domain, and the inlined copy in the
+-- friends-filtered leaderboard). Owned by the `api` worker; generated from
+-- packages/domain/src/relationships-db.ts (RELATIONSHIP_SCHEMA_DDL) — keep in sync.
+--
+-- The query is `relationship_type = ?2 AND (requester_id = ?1 OR target_id = ?1)`, which
+-- SQLite already splits into one probe per side of the OR. But `relationship_type` was in
+-- neither index and neither index carried the other side's id, so every row the player
+-- appears in — of ANY type — cost an index read plus a table-row read, and the non-friends
+-- were then discarded. Those rows accumulate: an unfriend keeps the row as type 0, ignoring
+-- or muting a stranger inserts a type 0 row, pending requests are rows. And the query runs
+-- on every matchmake and every disconnect (the presence push to friends), so D1 row reads
+-- were roughly 2 x (all relationships) x (matchmakes).
+--
+-- These two indexes cover each half: seek to (player, Friend), read the other id off the
+-- index, never touch the table. Reads become one per actual friend.
+--
+-- (target_id, relationship_type, requester_id) subsumes the old (target_id) index, so that
+-- one goes. The unique (requester_id, target_id) index stays — it is the pair constraint
+-- and what the single-pair lookups use.
+
+CREATE INDEX IF NOT EXISTS idx_relationship_requester_type
+  ON relationship (requester_id, relationship_type, target_id);
+CREATE INDEX IF NOT EXISTS idx_relationship_target_type
+  ON relationship (target_id, relationship_type, requester_id);
+DROP INDEX IF EXISTS idx_relationship_target;

packages/domain/src/relationships-db.ts

@@ -40,7 +40,12 @@ export const RELATIONSHIP_SCHEMA_DDL: string[] = [
 		target_muted INTEGER NOT NULL DEFAULT 0
 	)`,
 	`CREATE UNIQUE INDEX IF NOT EXISTS idx_relationship ON relationship (requester_id, target_id)`,
-	`CREATE INDEX IF NOT EXISTS idx_relationship_target ON relationship (target_id)`,
+	// Covering indexes for getFriendIds: each half of its OR seeks to (player, type) and reads
+	// the other id off the index. See apps/api/migrations/0030_relationship_friend_index.sql.
+	`CREATE INDEX IF NOT EXISTS idx_relationship_requester_type
+		ON relationship (requester_id, relationship_type, target_id)`,
+	`CREATE INDEX IF NOT EXISTS idx_relationship_target_type
+		ON relationship (target_id, relationship_type, requester_id)`,
 ]
 
 /** A stored relationship row (snake_case columns, one row per player pair). */