diff --git a/apps/api/migrations/adr091_rollback.sql b/apps/api/migrations/adr091_rollback.sql
new file mode 100644
index 00000000..9b8e92ed
--- /dev/null
+++ b/apps/api/migrations/adr091_rollback.sql
@@ -0,0 +1,9 @@
+-- adr091 rollback: drop aider_events + indexes
+-- 2026-04-20 @ Asia/Taipei
+-- 僅在 schema 誤套 / 緊急回滾時使用；資料不可復原
+
+DROP INDEX IF EXISTS aider_events_payload_gin;
+DROP INDEX IF EXISTS aider_events_ts_idx;
+DROP INDEX IF EXISTS aider_events_type_ts_idx;
+DROP INDEX IF EXISTS aider_events_session_idx;
+DROP TABLE IF EXISTS aider_events CASCADE;