Notebook E2E: the notebook's own state spelling (main.App.messages.getValue/setValue) #177

User decision 2026-10-04: remember_saveable is supported and UI.ipynb cells 9-13 run as written. pythonx-compose shipped remember_saveable (pythonx-compose #102) and removed state() (#101) on top of #174. Completion: ksp-fixtures/notebook-e2e main.py and cells 9-13 use main.App.messages.getValue()/setValue(); 20/20 against the pythonx-compose develop wheel.