[www] Fix broken undo() implementation.
@@ -326,7 +326,7 @@ def undo(session_id: int, n: int):
for _ in range(n):
env, _ = session.states.pop()
env.close()
- _, old_state = session[-1]
+ _, old_state = session.states[-1]
session.last_use = time()
return jsonify({"state": old_state.dict()})
