- Replace truncated 12-char UUID with full 32-char UUID (128-bit entropy)
- Add validate_session_id() regex check to prevent path traversal
- Add _check_session_id() guard on all 6 API endpoints
- Change _step_counter from module global to contextvars.ContextVar
- Filter None values from node_state before merging into agent_state
- Log save_session failures instead of silently swallowing them
- Add finishStreaming() in catch/finally blocks to prevent UI lockup
- Fix broken multiline docstring in chat() endpoint