fix(test): make ai_credits_reaper.rs resilient to accumulated stale holds

The sweep query is intentionally global (matches the real cron
reaper), but against a persistent, never-reset test database re-run
many times over a debugging session, other tests' un-captured/
un-released reservations eventually go stale and get picked up
alongside this test's own hold, breaking the exact-match assertion
(observed: 6 expired holds instead of 1). Clear pre-existing stale
'held' rows first, matching the clean slate a continuously-running
production reaper would actually maintain.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/db/tests/ai_credits_reaper.rs

@@ -36,6 +36,20 @@ async fn expired_hold_is_swept_and_credits_return_to_available() {
 
     AiCreditsRepository::ensure_wallet(&pool, user_id).await.unwrap();
 
+    // This test's sweep query below is intentionally global (it mirrors the
+    // real cron reaper, which sweeps every wallet, not just one) - in a real
+    // deployment the reaper runs continuously so nothing stays 'held' past
+    // its expiry for long. Against a persistent test database re-run many
+    // times over a session (not wiped between CI runs), other tests'
+    // reservations that were never captured/released can accumulate and go
+    // stale, which would make the exact-match assertion below flaky. Sweep
+    // those first so this test starts from the same clean slate a real
+    // continuously-running reaper would maintain.
+    sqlx::query("DELETE FROM ai_reservation_holds WHERE status = 'held' AND expires_at < NOW()")
+        .execute(&pool)
+        .await
+        .unwrap();
+
     let hold = AiCreditsRepository::try_reserve_credits(&pool, user_id, "help_answer", 4, None, None)
         .await
         .expect("reserve");