Use the turn index for turn-scoped item pagination (#54351)

## Why

A thread-wide index can scan earlier turns when a turn's final item page is underfilled.

## What changed

Force `idx_thread_items_by_turn_page` for turn-scoped item queries when neither `item_ids` nor `after_updated_at_ordinal` is set.

GitOrigin-RevId: 63c86fafa08446351a5d9828b479c497c76a8555

codex-rs/thread-store/src/local/thread_history/segment_paging.rs

@@ -292,11 +292,18 @@ pub(super) async fn page_item_rows(
         let mut query = QueryBuilder::<Sqlite>::new(
             r#"
 SELECT turn_id, item_id, rollout_ordinal, updated_at_ordinal, created_at_ms, started_at_ms, completed_at_ms, item_json
-FROM thread_items
-WHERE thread_id =
-            "#,
+FROM thread_items"#,
         );
-        query.push_bind(segment.rollout_id().to_string());
+        if params.turn_id.is_some()
+            && params.item_ids.is_none()
+            && params.after_updated_at_ordinal.is_none()
+        {
+            // A thread-wide index can scan earlier turns when a turn's final page is underfilled.
+            query.push(" INDEXED BY idx_thread_items_by_turn_page");
+        }
+        query
+            .push(" WHERE thread_id = ")
+            .push_bind(segment.rollout_id().to_string());
         push_segment_range(&mut query, segment)?;
         if let Some(after_updated_at_ordinal) = params.after_updated_at_ordinal {
             query