feat: implement MongoDB test database reset for clean test sessions

backend/db/db.py

@@ -579,29 +579,38 @@ def ensure_mongodb_indexes(client=None, db_name=None):
             coll.create_index(keys, **kwargs)
 
 
-# Clear test data at import time so tests start with a clean slate.
-if os.environ.get('DB_ENV', 'prod') == 'test':
-    if USE_MONGODB:
-        # Drop the entire MongoDB test database for a fresh start. Only do this
-        # for clearly test/e2e database names as a safety guard.
-        if _mongo_db_name and _mongo_db_name.endswith(('_test', '_e2e')):
-            get_mongo_client().drop_database(_mongo_db_name)
-    else:
-        child_db.truncate()
-        task_db.truncate()
-        routine_db.truncate()
-        routine_items_db.truncate()
-        routine_schedules_db.truncate()
-        routine_extensions_db.truncate()
-        reward_db.truncate()
-        image_db.truncate()
-        pending_reward_db.truncate()
-        pending_confirmations_db.truncate()
-        users_db.truncate()
-        tracking_events_db.truncate()
-        child_overrides_db.truncate()
-        chore_schedules_db.truncate()
-        task_extensions_db.truncate()
-        refresh_tokens_db.truncate()
-        push_subscriptions_db.truncate()
-        digest_action_tokens_db.truncate()
+# Clear test collections at import time so tests start with a clean slate.
+# Only TinyDB path — MongoDB cleanup is handled explicitly via reset_mongo_db().
+if os.environ.get('DB_ENV', 'prod') == 'test' and not USE_MONGODB:
+    child_db.truncate()
+    task_db.truncate()
+    routine_db.truncate()
+    routine_items_db.truncate()
+    routine_schedules_db.truncate()
+    routine_extensions_db.truncate()
+    reward_db.truncate()
+    image_db.truncate()
+    pending_reward_db.truncate()
+    pending_confirmations_db.truncate()
+    users_db.truncate()
+    tracking_events_db.truncate()
+    child_overrides_db.truncate()
+    chore_schedules_db.truncate()
+    task_extensions_db.truncate()
+    refresh_tokens_db.truncate()
+    push_subscriptions_db.truncate()
+    digest_action_tokens_db.truncate()
+
+
+def reset_mongo_db():
+    """Drop the MongoDB test/e2e database for a totally fresh slate.
+
+    Only acts on database names ending with ``_test`` or ``_e2e`` as a
+    safety guard against accidentally dropping production data.  Call this
+    once at the start of a test session or deployment seed step.
+    """
+    if not USE_MONGODB:
+        return
+    if not _mongo_db_name or not _mongo_db_name.endswith(('_test', '_e2e')):
+        return
+    get_mongo_client().drop_database(_mongo_db_name)