perf(server): drop three unused indexes on the sessions table

server/api/store/pg/migrations/017_drop_unused_session_indexes.tx.down.sql

@@ -0,0 +1,10 @@
+-- Restores the index set from 001.
+CREATE INDEX IF NOT EXISTS sessions_username_idx ON sessions USING btree (username);
+
+--bun:split
+
+CREATE INDEX IF NOT EXISTS sessions_type_idx ON sessions USING btree (type);
+
+--bun:split
+
+CREATE INDEX IF NOT EXISTS sessions_closed_started_idx ON sessions USING btree (closed, started_at);

server/api/store/pg/migrations/017_drop_unused_session_indexes.tx.up.sql

@@ -0,0 +1,27 @@
+-- Three indexes from 001 that no query in either repo can reach, maintained on every session
+-- insert and update for nothing. IF EXISTS because operators may already have dropped them by
+-- hand, and an error here fails the boot.
+--
+-- There is no read-path trade to weigh: these back no filter, no sort and no constraint, so
+-- nothing gets slower.
+
+-- The session list accepts exactly three filter fields (device_uid, closed, active) and
+-- rejects anything else at the route, and its sort is hardcoded to started_at — username is
+-- reachable by neither.
+DROP INDEX IF EXISTS sessions_username_idx;
+
+--bun:split
+
+-- Same for type. The type predicates that do exist are all on session_events, a different
+-- table, and are already served by its session_id/seat indexes.
+DROP INDEX IF EXISTS sessions_type_idx;
+
+--bun:split
+
+-- Redundant rather than merely unused: closed is a near-constant (a session is closed for all
+-- but the few minutes it is live), so (closed, started_at) is a strictly fatter duplicate of
+-- sessions_started_at_idx and loses to it on cost for every shape that exists — including the
+-- one it looks tailor-made for, the recording-conversion worker's
+-- "WHERE closed AND recorded AND NOT converted ORDER BY started_at DESC". If that worker ever
+-- shows up as a cost, the index it wants is a partial one on the backlog alone, not this.
+DROP INDEX IF EXISTS sessions_closed_started_idx;